Ahluwalia, D.V. & Wu, T.-Y., "On the magnetic field of cosmological bodies", Lett. Nuovo Cimento 23 406-408 1978.

Rotating mass produces magnetic field by a "mass current density". Calculate expected fields for the planets. Suggest an experiment using a copper sphere of diameter 20 cm rotating at 1000 rev/sec and giving a field of 10⁻¹³ T.

Angenheister, G., "Die physikalische Natur des erdmagnetischen Feldes", Phys. Zeitsch. 26 305-320 1925.

Blackett (1947) says Angenheister "stressed that the assumption of an electric charge density [rotating with the Sun/Earth] proportional to the mass density gives nearly the correct ratio for the magnetic fields of sun and earth. (This is equivalent to the Blackett equation.) He clearly recognized the physical difficulties of assuming the existence of real charges of such a magnitude, and of the large electric fields which must accompany them, in an electrically conducting material such as the earth's core".

Anonymous, Observatory 69 100-105 1949.

(Cited as Blackett (1949) by some authors.)

Report of RAS Geophysical Discussion, 25 February 1949. (This was also reported by Gold, 1949.)

 

Runcorn mentioned that the solar field was now known to vary significantly in time, and that the terrestrial field also varied. He gave preliminary result of the mine work, but pointed out the problem of the field gradients caused by basement rocks, and admitted that so far there were no measurements of the variation of H with depth from a suitable site. He mentioned that the theory predicted an effect from an E-W gorge.

Blackett suggested (for the first time as far as I can see) the static (gold) cylinder experiment.
Rosenfeld mentioned that while Pauli's formulation of the quantum theory of the electron could give a small contribution to the Earth's field, this would be very small.

Gold discussed various theoretical aspects.

(It is irrelevant in the present context, but interesting to note that B.C.Browne reported Bullard's early work on dynamo theory.)

Arley, N., "Blackett's hypothesis of the magnetic field of rotating bodies", Nature 161 598-9 1948.

Proposes various objections to Blackett's equation being more than coincidence.

 

The following paper by Fuchs shares the same heading/title.

Arley, N., Andreason, P., Esperson, J. & Olsen, J., "Magnetic investigations on the 'Galathea' expedition", Nature 171 384-385 1953.

A preliminary report of the Galathea's attempt to measure the variation of magnetic field with depth in the ocean.
See Esperson et al. (1956) for the full report.

Arrhenius, 1903.

Schlomka (1933) says Arrhenius produced a "rotation of surface negative charge" theory.

Atanasov, D., "Magnetic field of a charged rotating sphere in relation to an arbitrary point on its surface" (in Bulgarian), Tekh. Misul (Bulgaria) 9 No. 3 89-94 1972.

Physics Abstracts had: "It is shown mathematically that when a circle having electric charges fixed on its circumference is rotated about its centre, an electrostatic field and a magnetic field are produced at each point of the circle. Hence it is concluded that a charged rotating sphere produces a magnetic field at any point on the surface of the sphere and rotating with it at the same angular velocity."

Is this just re-inventing the wheel, or is there something new?

Babcock, H.W., "Zeeman effect in stellar spectra", Astrophys. J. 105 105-119 1947a.

The first measurement of the magnetic field of a star. It was this measurement, of 78 Virginis, which triggered Blackett's interest. (There is no discussion of the origin of the field.)

Babcock, H.W., "Remarks on stellar magnetism", Publ. Astr. Soc. Pac. 59 112-124 (and Plate XI) 1947b.

"It is noteworthy, although perhaps fortuitous, that within the limits of observation error, and within our assumptions of the spin of 78 Virginis, the magnetic dipole moment of each body [Earth, Sun, 78 Virginis] is proportional to its angular momentum".

Several other stars of the same spectral class as 78 Virginis had comparable magnetic fields.

 

"Received April 30, 1947. Read at the June meeting of the Society". He refers to the earlier work of Swann, Swann & Longacre, and Schlomka, but did not know of the concurrent work of Blackett.

 

Note that, for a star, the (integrated) magnetic dipole moment is measurable only if the axis of rotation of the star is along the line of sight; the angular momentum is then not measurable, and can be assigned only statistically.

Babcock, H.W. "Magnetic fields of astronomical bodies", Phys. Rev. 72 83 1947c.

A short note in which he suggests extending the dipole moment/angular momentum ratio to galaxies, but also cautions the reader by referring to Chapman's (1929) scepticism.

Barnett, S.J., "Magnetization and rotation", Amer. J. Phys. 16 140-147 1948.

A good review of the classical effects due to the differential inertia of electrons and positive ions, and of the gyromagnetic effects due to the electron orbital and spin angular momentum. These are all far too small to be relevant to cosmic bodies.

He then has a brief, but good, discussion of the papers of Schuster (1912), Wilson (1923) and Angenheister (1925).

Barnóthy, J.M., "The problem of elementary particles and the origin of the geomagnetic field", Budapest, Hungarian Inst. Met. Terr. Mag., Papers Terr. Mag. No.2. 46pp. 1947.

According to Cowling (1947), Barnóthy was influenced by Eddington, and proposes "an explanation of elementary particles in terms of serial universes" such that "there is an imaginary mass, behaving like an electric charge, associated with protons and neutrons". Cowling points out that this would produce a large electrostatic field, which "Barnóthy declines to consider for the present".

There is an editorial comment in Cowling's paper saying that Barnóthy was not influenced by Blackett's (1947) paper, as Barnóthy had submitted a similar paper to Nature in 1946.

Bauer, L.A., The physical theory of the Earth's magnetic and electric phenomena – No. V. On the formation of the Earth's field", Terr. Magn. Atmos. Electr. 17 75-96 1912a.

He refers to the modification of the horizontal field component (produced by a rotating-charge theory) as seen by an observer rotating with the Earth (Schuster (1912), but only as a possible way of accounting for the (apparently) observed relative increase of field near the equator; he does not expect the theory to account for the dipole field.

Bauer, L.A., "The physical theory of the Earth's magnetic and electric phenomena – No. VI. On the origin of the Earth's magnetic field", Terr. Magn. Atmos. Electr. 17 115-140 1912b.

"A summary of the chief results of this article was presented at a meeting of the Astronomical and Astrophysical Society of America, Pittsburgh, August 28, 1912."

He investigates how the (separated) charge density must vary with latitude if it is to account for the zonal part of the non-dipole field.

Bauer, L.A., "A consistent theory of the origin of the Earth's magnetic field", J. Washington Acad. Sci. 3 No. 1 1-7 1913a.

"Presented before the Philosophical Society of Washington, December 7, 1912; for fuller publication see Terrestrial Magnetism, Vol. 18, 1913." But in fact not published there.

He quotes the previous ideas of charge separation as a possible way of explaining the dipole field, but in this short paper he is more concerned with explaining the zonal non-dipole field in terms of non-uniformity of the charge separation, referring the reader to Bauer (1912b) for more detail.

Bauer, L.A., "On the origin of the Earth's magnetic field", Phys. Rev. (2) 1 254-257 1913b.

"Presented before the American Physical Society and Section B of the AAAS, Cleveland, December 30, 1912. The abstract also contains the chief results of the author's paper on 'Cosmical magnetic fields' presented before the joint session of A and B, December 31, 1912. To be published in J. Terr. Magn. Atmos. Electr., Vol. 18, 1913." But in fact not published there.

This is an extended abstract of a paper using the ideas of Bauer (1912b). A new concept is that he says that if the charge distribution were on the Earth's spheroidal surface, it would also account for the observed g₃⁰ and g₅⁰ terms.

 

There is no reference to the previous papers on the subject, but this is only an abstract.

Bauer, L.A., "The Earth's magnetism", Bedrock (London) 2 No. 3. 273-294 Oct 1913c.

"The Halley Lecture, 1913. Delivered in the schools of the University of Oxford, May 22^nd, 1913."

Also reprinted "after revision by the author and with added illustrations" as Smithsonian Inst., Rep. 1913, 195-212, with 9 plates".

 

These references are in two Terr. Mag. "List of recent papers". The paper is not referenced elsewhere, so is probably only a non-technical review.

Bauer, L.A., "Cosmical magnetic fields". "To be published in J. Terr. Magn. Atmos. Electr., Vol. 18, 1913d."

Although the publication of this paper was predicted in Bauer 1913a,b, it does not appear in volumes 18, 19 or 20!

Benfield, A.E., "The possible magnetic field of a rotating metallic body containing a stress gradient", Phys. Rev. 75 211-213 1949.

Suggests that a small effect might be observed due to charge separation.

Benfield, A.E., "Magnetism and the rotation of celestial bodies", Nature 166 31 1950…

Points out that charge separation theories such as that of Berlage (1950) would give very large internal electric fields.

Berlage, H.P., "The fundamental relation between the magnetic moment and the structure of rotating bodies", (Letter in) Nature 165 242-243 1950.

Suggests the radial separation of (real) charge in celestial bodies. The net charge is then zero, so there would be no external electric field.

But see Benfield (1950).

Blackett, P.M.S., "The magnetic field of massive rotating bodies", Nature 159 658-666 1947.

Using the magnetic fields of Earth, Sun, and 78-Virginis (he had learnt about Babcock's measurements), he resurrected the idea of some "fundamental" property of rotation giving a fictitious current density and hence a magnetic field for a massive rotating body; (P/U)=bG^0.5/2c (in cgsemu). He was struck by the fact that not only were the ratios (P/U) (of the magnetic dipole moment to angular momentum) almost the same for the three bodies, but that b was very close to unity.

He says he discovered the expression for the Earth and Sun himself, and only later found the previous literature. But he does give an excellent summary of the previous papers.
This 17 May publication is of the paper Blackett presented to the Royal Society Discussion Meeting on 15 May. It marks the start of the post-war renewed interest in such theories.

 

It was at this meeting that the geophysicist Bullard suggested that measuring the variation of the geomagnetic field with depth could be a test of (one possible interpretation of) the theory. This led to Bullard suggesting the Hales & Gough measurements in South Africa, and to Blackett suggesting and funding the Runcorn et al. measurements in England. Blackett himself considered but rejected the direct test of measuring the field produced by a rapidly rotating body in the laboratory; instead he performed the static test described in Blackett (1952).

Blackett, P.M.S., "The magnetic field of massive rotating bodies", Phil. Mag. (7) 40 125-150 1949a.

Presents Babcock's field measurements on further stars, and discusses the Hales & Gough (1947) and Runcorn (1948) mine experiments. It is a good historical review of most of the earlier work, with discussion of various aspects of the theory.

"This paper was prepared for, and read at, the Eigth Solvay Conference in Brussels in October 1948."

Blackett, P.M.S., Observatory 69 100-105 1949.

See Anonymous (1949).

Blackett, P.M.S., "Magnetic fields of large rotating bodies",

abstract of the talk to be given at the Royal Institution of Great Britain Weekly evening meeting on Friday 8 April 1949.

Blackett, P.M.S., "A negative experiment relating to magnetism and the Earth's rotation", Phil. Trans. R. Soc. A 245 309-370 1952.

"A detailed study of the possibility of making a direct test of the Schuster-Wilson hypothesis, by measuring the very small magnetic field of the order of 10⁻¹³ T which would be produced by a rotating body of reasonable size in the laboratory, led me to conclude that the experiment would perhaps be possible but would certainly be exceedingly difficult."

 

Describes the design and construction of a very sensitive astatic magnetometer, of noise level 10^‑13 T and period 30 s. A plausible extension of the Schuster-Wilson hypothesis predicts that a stationary massive body would give a field as seen a stationary observer because of its rotation with the Earth. The magnetometer was used to look for the 10⁻¹² T field expected from a static gold cylinder (10 cm diameter x 10 cm long), but any observed field was less than 10% of this.

 

The magnetometer was housed in a non-magnetic hut, in a corner of a field at the University's Jodrell Bank Botanical Research Station, 200 m from the rapidly developing Radio-Astronomy Station. It was later used to measure rock samples, and was a major contributor to the rebirth of palaeomagnetism in the UK. The gold cylinder was hired from Johnson Matthey of London, and kept in a safe in the Physical Laboratrories at Manchester. Once or twice I "escorted" Jim Pickering out to Jodrel Bankl, and helped him with the measurements.

Brunt, D., "The general magnetic field of the Sun", Astron. Nachrichten 196 No. 4690 169-178 1914.

For a charge-separation theory, with the main body of the Sun having a positive charge, for a positive ion in the solar photosphere to be held by gravity against the electric field he shows that the charge is quite insufficient to produce the observed magnetic field. He also briefly summarizes and discusses the way the surface magnetic field produced by the various theories discussed by Schuster (1912) and Swann (1912) would depend on radius and angular velocity.

Caussé, M., Thèse, Fac. Sci. de l'Univ. de Paris, 26ff., 1949.

 

Caussé, M., "Les élements de la relativité cinématique" Ann. de Phys. (12) 4 760-805 1949.

Milne (1950) says Caussé used a theory of kinematic relativity to explain the existence of magnetic field in rotating bodies, but Milne does not accept it.

Chapman, S., "Cosmical magnetic phenomena", Nature 124 19-27 1929.

"Rouse Ball Lecture delivered at Cambridge on May 31."

A non-technical general review. "These asymmetric features [the non-dipole field] must be ascribed to causes which cannot be fundamental, and as they are not greatly inferior to the axial fields, it seems unnecessary to invoke fundamental hypotheses for the latter. Therefore in my opinion cosmical magnetism is probably only a secondary, though possibly widespread, phenomenon, and not a universal fundamental one like gravitation."

Chapman, S., "The magnetic field of the Moon?", (Letter in) Nature 160 395 1947.

Blackett's formula would give a polar field of about 100 nT. Suggests sending a rocket equipped with a total-intensity magnetometer.

Published 20 September 1947.

 

(Chapman refers to a Blackett Proc. R. Soc. paper as being "in press", but I cannot find such a paper.)

Chapman, S., "Variation of geomagnetic intensity with depth", (Letter in) Nature 161 52 1948a.

Points out that the formula given by Runcorn in Hales & Gough (1947) cannot be true in general.
Published 10 January 1948. Followed by short reply by Runcorn (1948a).

Chapman, S., "The dipole moment of the supposed fundamental magnetic field due to rotation", (Letter in) Proc. Phys. Soc. 61 95 1948b.

Extends Blackett's argument (for spherical bodies) to more general axial symmetry. Points out there will then also be higher multipoles.

Chapman, S., "The supposed fundamental geomagnetic field", Ann. Geophysique 4 109-123 1948c.

Long-winded but thorough calculation of internal and external fields given by a current density proportional to mass motion. (Chapman gives a summary of the theory in Runcorn, 1948b.) For Earth he gives results for uniform density, and for two analytic models of radial density variation. The atmosphere will contribute only about 1 nT.

MS received 23 February 1948.

Chapman, S., "The main geomagnetic field", Nature 161 462-464 1948d.

Report of RAS Geophysical Discussion of 27 Feb 1948, in which Runcorn reported the November 1947 paper of Hales & Gough, and gave preliminary account of his own Lancashire mine work.

Published 27 March 1948. Note that this meeting was only 9 months after Blackett's Royal Society presentation; things moved fast in those pre-bureaucratic days!

Chapman, S., "Solar magnetism and the suggested fundamental magnetization by rotation", Mon. Not. R. Astr. Soc. 108 236-251 1948e.

Gives general expression for calculating magnetic field inside spherically symmetric rotating body.
MS received 22 May 1948.

Chapman, S. & Bartels, J., "Geomagnetism", Oxford University Press, Oxford, 1940.

This is the classical (and only) textbook of the time, with a comprehensive survey of all that was known about geomagnetism then. Chapter 21 has a concise review of many of the rotation theories suggested previously.

Cowling, T.G. "Elementary particles and the geomagnetic field", Nature 160 847 1947.

A criticism of Barnóthy (1947).

Cranna, K.G. & Papini, G., "A proposed test of Blackett's hypothesis using superconductors", Nuovo Cimento 52B 241-243 1967.

Suggest that the superconducting-loop magnetometer proposed in Papini (1966) could be used to detect the field from a copper sphere of diameter 20 cm rotating at 10 000 rad/sec.

Darwin, C., "Electron inertia and terrestrial magnetism", Proc. R. Soc. London A 222 471-476 1954.

For any feasible acceleration/deceleration of the Earth's spin, the magnetic effect of electron inertia would be utterly trivial.

Décombe, 1922

Schlomka (1933) says Décombe produced a "rotation of quasi-charge, or quasi current" theory.

De Sabbata, V. & Gasperini, M., "The magnetic field of the Earth", Lett. Nuovo Cimento 27 449-453 1980.

Use their own cosmological theory to predict an axial dipole field.

Eichenwald, A.A., (date unknown).

Kuznetsov (1983) says "The magnetic field caused by the rotation of electrical charges around the Earth's axis and directed along the radius of the disc on which these charges are induced was observed in A.A. Eichenwald's experiments", and gives the reference as Tamm, I.E., "Fundamental principles of the theory of electricity" (In Russian), Nauka, Moscow, 1966.

Einstein, A., 1924.

Schlomka (1933) says Einstein produced a "rotation of quasi-charge, or quasi current" theory.

Esperson, J., Andreason, P., Egedal, J. & Olsen, J., "Measurements at sea of the vertical gradient of the main geomagnetic field during the 'Galathea' expedition", J. Geophys. Res. 61 593-624 1956.

This 1950-52 Danish expedition was primarily for biological investigations, but at a late stage of planning the magnetic measurements were added.

Either a modified BMZ magnetometer (to measure the vertical component Z), or a modified LaCour magnetometer rotated in gimbals once in 10 minutes (to measure he magnitude H of the horizontal component), each using photographic recording, was installed in a 10 cm thick 800 kg non-magnetic aluminium-phosphor-bronze sphere, and lowered to depths down to 5000 m. Eventually the noise level was reduced to 10-20 nT, and some good magnetic measurements were obtained, but (partly because of a winch breakdown) only at sites where there were large crustal gradients.

 

Arley et al. 1953 was a preliminary report.

Fuchs, J., "Blackett's hypothesisis of the magnetic field of rotating bodies", Nature 161 599 1948.

Argues that Blackett's equation is better expressed in the more general form P/(U/2) = m₀(e₀/g)^0.5, where g=1/G (so that g appears in the denominator rather than the numerator of the force equation, as does e₀). But note that he is still working in un-rationalized units.

This paper is immediately after that of Arley, and shares the same heading/title.

Gething, P.J.D., "Rotation and magnetism in the world-models of kinematic relativity", Mon. Not. R. Astron. Soc. 112 578-582 1952.

Shows that on Milne's (1950) theory a symmetrical mass distribution would produce no magnetic field. An asymmetric mass distribution would produce a field, but there would then not be proportionality between dipole moment and angular momentum. So questions Milne's claim to have established a theoretical basis for Blackett's formula."

Gião, A., "Sur le magnétisme des masses en rotation", C.R Acad. Sci. Paris. 224 1813-1815 1947.

Seems to use a (unitary theory?) space-time approach to derive the Blackett formula.

Report of 30 June 1947 meeting of the Academy, 6 weeks after Blackett's presentation to the Royal Society.

Gião, A., "Sur la relation entre le moment magnétique et le moment de rotation des masses sphérique", C.R. Acad. Sci. Paris 225 924-926 1947.

More theory for production of dipole moment.

Report of of 3 November 1947 meeting of the Academy.

Gião, A., "Sur l'effet mécano-magnétique a l'interier des masses sphérique en rotation; Application au champ magnétique terrestre", C.R. Acad. Sci. Paris 226 645-647 1948.

A space-tine approach to deriving the variation of the field with depth near the surface. It appears to give a gradient 2-3 times larger than the Runcorn/Chapman value.

 

Report of 9 February 1948 meeting of the Academy.

Gião, A., "Propriétés magnétique de la matière en rotation", Repr. Gazetade Matemática, Lisboa, Nos. 34 e 35, 6pp, 1946-1948.

 

Gold, T., "Rotation and terrestrial magnetism", Nature 163 513-515 1949.

Report of RAS Geophysical Discussion of 25 Feb. 1949

See Anonymous( 1949) for notes.

Haalk, H., "Über das Vorhandensein einer magnetischen Wirkung durch rotirende Massen und die Ursache des Erd- und Sonnenmagnetismus", Zeit. f. Geophys. 5 359-365 1929.

Some sort of charge-separation theory.

Criticized by Schlomka (1932).

Haalk, H., "Über eine neue physikalische Erklärung der Ursache des Erd- und Sonnenmagnetismus und des luftelektrischen Vertikalstrome", Zeit. f. Geophys. 12 112-123 1936.

More charge-separation theory.

The theory is criticized by Schlomka (1937) because of the very large internal electric fields which would be produced.

Haalk, H. "Kann bei sehr hohen Drucken in einer Masse durch einen Druckgradienten eine Ladungstrennung hervorgerufen werden? Zeit. f. Physik. 105 81-87 1937.

The ideas of this paper are discussed in more detail in Haalk (1938).

Haalk, H., "Über die physikalischen Ursachen des Magnetismus der Erde", Gerlands Beitr. Geophys. 52 243-269 1938.

This paper has an English abstract, from which the following is a summary.

Because of the high temperature and pressure the material is ionized. The pressure gradient then gives charge separation of the correct sign. Using the Earth as a calibration, the theory then gives the right magnitude for the Sun's field.

 

(In the 1938 paper Haalk goes on to discuss crustal magnetization, and suggests that the secular variation comes from changes in crustal magnetization because of temperature variations.)

Hale, G.E., "Note on Sutherland's paper", Terr. Mag. Atmos. Electr. 13 158 1908.

See Sutherland (1908).

Hale, G.E., "Preliminary note on an attempt to detect the general magnetic field of the Sun", Terr. Magn. Atmos. Elect. 17 173-178 1912.

(The magnetic fields of sunspots had been measured, by the Zeeman splitting they produced in spectrum lines, in 1908. But any general solar field was much smaller.)

Measured the variation of the (very small) Zeeman splitting of several spectrum lines as a function of latitude. The results were very noisy, but were consistent with the field being that of a dipole, of the same polarity as that of the Earth. At that time they did not have a laboratory calibration for those lines ("Mr Babcock is trying to measure them" –is this the H.W.Babcock of the stellar field measurements?), so no value is given for the field magnitude.

 

His interpretation is in terms of rotating charge densities, of opposite sign at different radii.

 

(It is interesting that the first publication of this result was in a geophysics journal.)

Hale, G.E., "Preliminary note on an attempt to detect the general magnetic field of the Sun", Publ. Astron. Soc. Pacific 25 28- 1913a.

Hale, G.E., "Preliminary results of an attempt to detect the general magnetic field of the Sun", Astrophys. J. 38 27-98 1913b.

N.B. The summary is at the end of the paper.

 

Starts by discussing theories of production of geomagnetic field, and assumpes that the Sun's field will have the same origin. By now "Mr. Babcock has managed to make some laboratory calibrations", the surface polar field magnitude "is of the order of 50 gauss" (5 mT, about 10 times that of the Earth).

 

With the publication of these results there were now two "massive rotating bodies" (Earth and Sun) for which the magnetic field was known. (The measurements were very difficult, and it is now thought that Hale's result probably over-estimated the magnitude of the dipole field present then.)

Hale, G.E., "The Earth and Sun as magnets", Pop. Sci. Mon. (Lancaster, Pa.) 73 No. 2 105-124 1913c.

This reference is in a Terr. Mag. "List of recent papers". It is not referenced elsewhere, so is probably only a non-technical review.

Hale, G.E., "Magnetism of celestial bodies", Sci. Amer. Sup. 76 196-198 (with 10 figures) 1913d.

"An investigation in solar physics conducted by the Mount Wilson Observatory."

This reference is in a Terr. Mag. "List of recent papers". It is not referenced elsewhere, so is probably only a non-technical review.

Hales, A.L. & Gough, D.I., "Blackett's fundamental theory of the Earth's magnetic field", (Letter in) Nature 160 746 1947.

Results of variation of field with depth in the Blyvooruitzicht diamond mine in Witwatersrand, S. Africa; appeared to support Blackett, but now thought to be due to the crustal field from the highly magnetic rocks. Includes the results of a calculation by Runcorn, but see criticism of this by Chapman (1948a).

Published 29 November 1947, only 6 months after Blackett's lecture!

Helmholtz, H. "Versache über die elektromagnetische Wirkung elektrischer Convection, ausgeführt von Hrn. Henry A. Rowland der J. Hopkins' Universität in Baltimore", Monats. der kön. preuss. Akad. der .Wiss. Berlin pp211-216 1876a.

This is a report, given by Helmholtz to the Berlin Academy of Sciences on 16 Mar 1876, of Rowland's experiment, which was done in Helmholtz' laboratory in Berlin. (See Rowland, 1878.) In it Helmholtz mentions that at his suggestion Schiller had carried out some unsuccessful experiments with the same aim as Rowland; however Rowland had developed the idea of his experiment entirely independently.

Helmholtz, H., "On the electromagnetic action of electric convection", Phil. Mag. (5) 1 233-237 1876b.

A report by Helmoltz of the experiment by Rowland

This is subtitled "A report on some experiments carried out by Mr. Henry A. Rowland, of J. Hopkins University in Baltimore"; it appears in a section called "Intelligence and Miscellaneous Articles", and is a direct translation of Helmholtz (1876a).

Holm, G.R., "Gravitation and gyromagnetism", J. Geophys. Res. 57 527-530 1952.

Extends previous field theories of his to produce a formula similar to that of Blackett.

Juergans, R.E., "On the convection of electric charge by the rotation of the Earth", Kronos 2 No.3 12-29 1977.

Rotating charge – external field reduced by a surrounding "plasma sheath" at high potential! Tries to support Velikovsky's ideas about sudden changes in the Earth's rotation by allowing the Earth to be carrying a large electrical charge. This could be changed in sign (and hence give a magnetic field reversal) by an "interplanetary bolt" from the plasma sheath!

Kelvin, Lord, (was W.Thomson) "Presidential Address", Proc. R. Soc. London 52 303-310 1892.

His theme is the need for the Sun to have a large magnetic field so that variations of it can affect the Earth. On p304 he has "Considering probabilities and possibilities as to the history of the earth from its beginning to the present time, I find it unimaginable but that terrestrial magnetism is due to the greatness and the rotation of the earth" and hence that other planets and the Sun will also be magnets. "Absolutely ignorant as we are regarding the effect … of straining the circumambient ether, we cannot say that the sun might not be 1000, or 10,000, or 100,000 times as intense a magnet as the earth."

 

Presidential Address, 30 November 1892.

Kumar, N. & Nandini, R., "Magnetic field due to self-gravity-induced electric polarization of a rotating body", Phys. Rev. D 7 3586-3589 1973.

Rotation of the gravity-induced electric polarization "is shown to generate an axial magnetic field of the right type and order for certain astrophysical bodies". In fact the calculation is done only for infinite–length rotating cylinder.

The authors do not appear to know of the other work in this field.

Kuznetsov, V.V., "A model of the Earth's core and its geomagnetic field" , Sov. Geol. & Geophys. 24 No.5 74-80 1983. (English translation of Geologiya i Geofizika 24 No.5 78-84 1983.)

"A model of the Earth's core is proposed in which the inner core is a superheated ultra-compressed solid high-density vapour …". Rotation of the resultant separated charges is then used to explain the production of the dipole field (and many other phenomena!).

Lébedèw, P., "Über die magnetische Fernwirkung rotierender Körper", Ann. d. Phys., Leipzig, 39 No. 14 840-848 1912.

Barnett (1948) says Lébedèw looked for a centrifugally produced charge separation by rotating small toroidal rings of various non-magnetic materials at speeds up to 500 rev/sec. Using an astatic magnetometer he could detect no field greater than about 100 nT; scaling from the Earth he was looking for an effect 100 times larger.

Bauer (1913a) says "This was this brilliant investigator's last work, he having died before the appearance of his paper".

Luchak, G., "On a generalization of Wilson's hypothesis", Phil. Mag. (7) 42 807-808 1951a.

A criticism of Papapetrou (1950).

Luchak, G., "A fundamental theory of the magnetism of massive rotating bodies", Canadian J. Phys. 29 470-479 1951b.

"A phenomenological theory based on a relativistically covariant generalization of Maxwell's equations … . The equations yield the Wilson-Blackett expression … .".

Mariani, J., C.R. Acad. Sci. Paris 206 1247- 1938; 211 430- 1940; 218 447- and 585- 1944, "Electromagnétisme et relativité" (Cahiers de Physique Theorétique, Paris, 1945) Part 1, and "Théorie des champes macroscopiques", pp ii + 98 (Paris, Centre de Documentation universitaire, 1947)..

Piaggio (1948) says these papers apply unified field theory to predict that a gravitational field must necessarily be accompanied by an electric field. Mariani then follows Sutherland in having a positive volume charge density compensated by a negative surface charge density.

Mariani, J., "On magnetism of celestial bodies", (Letter to) Phys. Rev. 73 78 1948.

Suggests a theoretical basis for Blackett's equation in terms of a rotating fictitious charge density.

He does not refer to his own earlier papers.

Milne, E.A., "Gravitation and magnetism", Mon. Not. R. Astron. Soc. 110 266-274 1950.

Says he "is unable to accept this claim [of Caussé's (1949) prediction that kinematic relativity explains the presence of magnetic fields in rotating bodies] in Caussé's form".

But then uses his own theory of kinematic relativity to produce a relation between field and rotation (for a galaxy) of the same type as Blackett's, but having additional non-dimensional factors. I think the factors would be such as to reduce the predicted field for the Sun, but Milne is "not inclined to consider this [application to the Sun] as a legitimate application of the theory" because (I think) of problems about absolute reference axis.

 

On his theory the field is not dipolar in its radial variation.

 

This is criticised by Gething (1952).

Moore, J.T. & Kuhlmann-Wilsdorf, D., "Charge separation due to hydrostatic pressure and its possible contribution to the geomagnetic field", Materials Sci. Engng. 3 183-185 1968.

An (over-) estimate of the dipole moment coming from pressure-induced charge separation is 10²⁰ times too small.
The authors do not refer to any of the other papers on the subject.

Neugebauer, T., "On a relationship between gravitation and magnetism" (in German), Acta Phys. Hungarica 1 151-165 1951.

Using certain assumptions, calculates the magnetic effect of a rotating body having a gravitational pressure-induced charge separation.

Papapetrou, A., "A 4-dimensional generalization of Wilson's hypothesis", Phil. Mag. (7) 41 399-404 1950.

A simple 4-d generalization of Wilson's 3-d result would lead to a very large electric field, so he looks for a way out of the problem.

This paper was severely criticised by Luchak (1951).

Papini, G., "A test of general relativity by means of superconductors", Physics Letters 23 No. 7 418-419 1966.

Proposes using a rotating superconducting loop.

This is the proposed magnetometer referred to in Cranna & Papini (1967).

Perry, J. & Ayrton, W.E., "A new theory of terrestrial magnetism", Phil. Mag. (5) 7 401-411 1879.

Following on from Rowland's (1876) experiment on the magnetic effect of a spinning charged disc, they propose that the Earth's field is produced because of a uniform surface charge density spinning with the Earth. They have a very long-winded calculation of the resultant internal uniform field and external dipole field. From the observed dipole moment they calculate the necessary charge density, and the corresponding electrostatic potential of the charged Earth, about 10⁶ V.

BUT, as Rowland (1879) points out, on p 407 they had wrongly simplified the product a^−5/2a³ to

 

a^−1/2 rather than a^+1/2; as a is the Earth's radius in centimetres, they underestimated the charge density, and hence potential, by a factor of 6x10⁸!

 

In an interesting aside, they claim that they had themselves in the autumn of 1876 designed apparatus to look for any magnetic effects of spinning charge, and were waiting for the dry Japanese winter to perform the experiment, when they read Rowland's 1876 paper!

 

(In their calculation they show that for a central dipole, on a sphere the field intensity varies as (1+3 sin² l)^0.5, where l is the latitude; they say this had been suggested as an empirical approximation for the geomagnetic field by Biot. I suspect that this is the first time this expression was derived.)

Pflüger, 1905/1906.

Schlomka, 1933, says Pflüger produced a "rotation of surface negative charge" theory.

Piaggio, H.T.H., "Magnetic field of massive rotating bodies", Nature 161 450 1948.

Prompted by Blackett's (1947) paper, he points out that Mariani had produced some (very abstruse) papers on a possible unified field theory approach from 1938-1948.

Pliner, I.G., "The magnetic field of massive rotating bodies" (in Russian), Priroda 37 16-24 1948.

(Abstract in Geophys. Abs. No. 137 p106 1949)

Procopiu, S., "Champ magnétique dû à la rotation d'une masse gravitationelle et à la rotation d'une charge eléctrique", Repr. Rev. Stiintifica "V. Adamachi" 34 No.1-2 73-74 1948.

 

Rowland, H.A., "On the magnetic effect of electric convection", Amer. J. Sci. (3) 15 30-38 1878.

Maxwell had predicted that a moving charge would act like an electric current "but that the action exists has not yet been proved experimentally or theoretically".

 

An annular part of an insulating disc of diameter 21 cm was made the central electrode of a symmetrical plane-parallel capacitor, and a voltage applied (through a slip ring) so as to induce a known charge on the disc surfaces. The disc was rotated at 61 rev/sec about a vertical axis. To measure any magnetic field resulting from the motion of the charge, an astatic magnetometer was used, having a magnet spacing of 18 cm, and with the lower magnet above the disc. The voltage was measuring by observing the spacing between two spheres at which a spark occurred.

 

There were many sources of noise, but he claims that the results were reproducible in good conditions. The agreement between predicted and measured magnetic field was about 5%; this difference was reduced if he used Weber's value for c, the speed of light, rather than Maxwell's value. (The value of c enters the calculation because of the need to convert the induced charge density from esu to emu. Rowland points out that the experiment could be used to measure c.)

 

This is the first experimental confirmation that a moving electrostatic charge behaves like a current; it was done in the laboratory of Professor Helmholtz in Berlin.

 

A note says "The idea of the experiment first occurred to me in 1868 and was recorded in a note book of that date.

 

In his 1879 paper Rowland says that at the time of this experiment he "suggested to Professor Helmholtz that a theory of the earth's magnetism might be based upon the experiment. But upon calculating the potential of the earth required to produce the effect, I found that it [4x10¹⁶ V] was entirely too great to exist without producing violent perturbations in the planetary movements, and other violent actions".

Rowland, H.A., "On Professors Ayrton and Perry's new theory of the Earth's magnetism, with a note on a new theory of the aurora", Phil.Mag. (5) 8 102-106 1879

He had read some (presumably shortened) version of the Perry & Ayrton 1878 paper, and did not believe their result. He does his own, much simpler calculation, to show that for a rotating surface charge to give the observed magnetic field, the external electric field would be enormous. In a "note in proof" he says he has now seen the full paper, and points out their algebraic mistake.

Runcorn, S.K., "(Reply to) 'Variation of geomagnetic intensity with depth' by Chapman", Nature 161 52 1948a.

Printed with Chapman's letter. Runcorn defends his (formally incorrect) formula as being an approximation valid for small deviations from uniform density.

Published 10 January 1948.

Runcorn, S.K., "The radial variation of the Earth's magnetic field", Proc. Phys. Soc. 61 373-382 1948b.

More detailed, correct, calculations. for Earth models (Also a suggestion that there would be field variations across an East-West range or canyon.)

An Appendix by Chapman outlines the theory given in more detail in Chapman (1948c).

Received 30 April 1948.

Runcorn, S.K., Benson, A.C. Moore, A.F. & Griffiths, D.H., "The experimental determination of the geomagnetic radial variation", Phil. Mag. (7) 41 783-791 1950.

Presents the results from 3 coal mines, depth about 850 m, in Lancashire, England, for which the (magnetic) basement rocks were at depth about 2500 m, and surface surveys showed smooth gradients. They measured the depth variation of Z with a BMZ , and that of H with a QHM, to about 1 nT. The experimental values were "near to the values predicted by a core theory, and significantly different from those predicted by a distributed theory".

Runcorn, S.K., Benson, A.C. Moore, A.F. & Griffiths, D.H., "Measurements of the variation with depth of the main geomagnetic field", Phil. Trans. R. Soc. A 244 113-151 1951.

Detailed discussion of the mine experiment. "Measurements in five [coal] mines in northern England provide evidence in favour of the core theory."

Salceanu, C., "Champ magnétique produit par la rotation d'une masse gravitationelle douée d'une charge eléctrique de volume" C.R. Acad. Sci. Paris 227 624-626 1948.

"The aim of this note is to give a theoretical justification to [Blackett's formula]"

Séance of 13 September 1948.

Schlomka, T., "Zur Haalckschen Theorie des Erdmagnetismus", Zeit. f. Geophysik 8 84-87 1932.

A criticism of Haalck (1929).

Schlomka, T., "Zur physikalische Theorie des Erdmagnetismus", Zeit. f. Geophysik 9 99-109 1933a.

Essentially the Erdmagetismus part of Schlomka (1933b).

Schlomka, T., "Gravitation und Erdmagnetismus. Teil I", Gerlands Beitr. Geophys. 38 357-406 1933b.

If the repulsions between electron/electron and proton/proton were each different (by a few parts in 10¹⁹) from the attraction between electron/proton, then the rotation of the resultant charge separation would lead to a magnetic dipole moment (and also provide gravity).

His Table 1 seems to be a quite comprehensive, if very terse, catalogue of previous theories; it includes several authors not otherwise cited in the literature, but unfortunately he does not give proper references.

Schlomka, T., "Zur neuen Haalckschen Theorie des Erdmagnetismus", Zeit. f. Geophysik 13 126-131 1937.

A detailed criticism of Haalck (1936).

Schrödinger, E., "The general unitary theory of the physical fields", Proc. R. Irish Acad. A 19 43-46 1943a.

 

Schrödinger, E., "The Earth's and the Sun's permanent magnetic fields in the unitary field theory", Proc. R. Irish Acad. A 19 135-148 1943b.

The first paper shows that his theory predicts that a "dipole" field (of whatever origin) would (outside the source) decay with distance with an exponential modification of the inverse-cube law; but he had only a very rough idea of the decay length. In the second paper he claims that the observed terrestrial field of external origin (at that time thought to be quite large) was very well fitted by his theory if he took the appropriate decay length.

BUT NONE OF THIS INVOLVES ROTATION. I have included these references just in case anyone else came across the titles and, as I did, thought they were relevant!

Schuster, A., "Recent total solar eclipses", Proc. R. Institution 13 273-276 1891.

"The form of the corona suggests a further hypothesis, which, extravagant as it may appear at present, may yet prove to be true. Is the Sun a magnet? … but may not a revolving body act like a magnet, and may not the earth's magnetism be similarly due the earth's revolution about its axis?" It can be shown … ." (but he does not!) that laboratory rotators would not show any measurable effect.

Royal Institution lecture of 13 February 1891.

Schuster, A., "Presidential Address to Section A", Brit. Assoc. Rep. 1892 627-635 1893.

One paragraph on p634 has "Is every large rotating mass a magnet? If it is, the Sun must be a powerful magnet." There is nothing else of relevance to rotation theories.

Address given 4 August 1892.

Schuster, A., "A critical examination of the possible causes of terrestrial magnetism", Proc. Phys. Soc. 24 121-137 15 April 1912a.

(Note that the abstract is at the end of the paper!)

He quotes his 1891-2 questions. He points out that for a rotating charge theory, if the effect of linear motion is to be nulled, this involves adding an extra, larger and opposite, horizontal component of magnetic field for an observer moving with the sphere; so an observer moving with the Earth would see the wrong geometry of field. He shows that if any effect were to produce a uniform volume magnetization proportional to angular velocity ("a rotating molecule may be a magnetic doublet"), then laboratory rotators would give very large fields.

 

So he then suggests "a moving molecule may behave as if it carried a moving charge", which leads to a surface magnetic field proportional to radius and equatorial velocity (the same as predicted by the Blackett formula). Scaling the theory to give the correct field for the Earth, the Sun's polar surface field would be 400 times larger, while a laboratory rotator would give a trivial field. But he then points out the problem that there are no observed effect for linear motion, so rules out this simple theory. He says that experiments on rapidly rotating bodies "are in progress in the Physical Laboratories of the University of Manchester". Presumably the null results were never published.

 

He briefly discusses the concept that if the electron/electron and proton/proton repulsions were less than the electron/proton attraction by 3 parts in 10³⁷ this could explain gravity, and possibly also (by some unknown mechanism) magnetic field.

 

Presidential Address, given 9 February 1912.

Schuster, A., "A critical examination of the possible causes of terrestrial magnetism", Elec. Rev. (Chicago, Ill.) 60 No. 16 763-764 20 April 1912b.

This is referenced in a Terr. Mag. "List of recent papers", but is not referenced elsewhere. It is probably essentially just a shortened version of his 1912a paper.

Shrivastava, C.P., "Spinning electron and earth's magnetism", Indian J. Theor. Phys. 31 No.1 33-34 1983.

The abstract is "The mechanical feature of a free electron has been emphasized. It is justified that the magnetism of earth is due to its rotation.", but the paper is 500 words of meaningless waffle.

Sirag, S.P., "Gravitational magnetism", (Letter in) Nature 278 535-538 1979.

He adds the magnetic field of the pulsar Hercules X-1 to give a fourth point on the Blackett diagram. Argues that Blackett's (negative) interpretation of the mine and (static gold cylinder) laboratory experiments was wrong, and urges direct experiment using a massive laboratory rotator.

He has some useful comments on some of the earlier papers.

 

Although he gives two other references for the measurement of the field of the pulsar, in fact these both go back to Trümper et al. (1977).

Surdin, M., "Sur l'origine du champ magnétique terrestre", C.R. Acad. Sci. Paris B 267 No.21 1181-84 1968.

A theory of his ("to be published" –presumably Surdin, 1971) predicts the occurrence and frequency of reversals.

Surdin, M., "Le champ électromagnétique fluctuant de l'univers. (Essai d'une Électrodynamique stochastique)", Ann. Inst. Henri-Poincaré 15 No.3 203-241 1971.

"An electromagnetic model of gravitation is advanced and a simple mathematical formalism is derived. This formalism is used to solve various problems, such as: the magnetic field of rotating bodies, … ."

A Professor of theoretical physics told me that the electrodynamic aspects of his work at the quantum level were dubious, but not disprovable. But he rejected any application to cosmic scales!

 

(In 1979 Surdin explains that "universal fluctuations of the electomagnetic field" induces electric dipoles of short duration; in a rotating body these dipoles are directed cylindrically radially, either inwards or outwards.)

 

The theory predicts that rotation leads to a randomly-reversing magnetic field at the centre of a sphere of magnitude H=G^0.5Mw/8^0.5cR in cgsemu (this is of the same form as the Blackett equation); the field decreases somewhat towards the surface. The field reverses randomly, the zero crossings having a Poisson distribution, with the typical spacing being the electromagnetic decay time of the sphere.

Surdin, M., "Magnetic field of rotating bodies", J. Franklin Inst. 303 493-510 1977.

Points out that on his theory the field decreases towards the surface, so was not disproved by the Runcorn et al. mine experiment. He also says that the Blackett's negative result was irrelevant; in effect Blackett had used M_goldw_earthR_earth, predicting 10⁻¹² T, while Surdin says he should have used M_goldw_earthR_gold, predicting 10⁻¹⁹ T; also the 30 s time constant of Blackett's magnetometer was far longer than the reversal time (the electromagnetic decay time of the gold cylinder).

He gives an account of his experimental work, in which he rotated (using air-bearings and an air-turbine) tungsten and phosphor-bronze cylinders (10 cm diameter, 15 cm long) at 500 rev/sec. His theory predicted a field of about 10⁻¹² T, reversing several hundred times per second. He used an axial pick-up coil surrounding the rotor, used a low-pass filter to reject noise at rotation frequency, and measured the auto-correlation of the resultant amplified output. He subtracted the auto-correlation for the stationary rotor from that for the spinning rotor and claimed that the results agreed with his theory.

Surdin, M., "The magnetic field of the planets", Nuovo Cimento 2C No.5 527-536 1979.

Gives a clearer picture of what his theory involves. Adds the planets, a neutron star, and the local galaxy to his list of predictions/comparisons; he approximates the conversion from the central field (predicted by his theory) to the equatorial surface field (as observed) by using the factor of 1/5, valid for the rotation of a sphere of uniform volume charge density. He points out that for the Moon the theory predicts a dipole field of magnitude 60 nT, much larger than that observed.

Sutherland, W., "A possible cause of the Earth's magnetism and a theory of its variations", Terr. Mag. Atmos. Electr. 5 73-83 1900.

This is the abstract of a paper presented in Australia; it contains no references.

For an electrically neutral Earth, having (larger) charge distributions of opposite sign at different radii, there would be no external electric field, but rotation would give the observed surface magnetic field. There would then be very large internal electric fields, of the order of 10¹⁰ V/m, but "it is quite probable that a solid dielectric in the Earth could stand this". There is only vague speculation about the origin of the charge separation. (He also speculates on the production of the non-dipole field, the daily variation, and magnetic storms.)

 

This is the first suggestion of rotating separated charges.

Sutherland, W., "The cause of the Earth's magnetism", Terr. Mag. Atmos. Electr. 8 49-52 1903.

Suggests that an effective charge separation could come from "a minute tendency of each [negative ion] of a molecular doublet [ionic bond] to turn further from the centre of the Earth than the [positive ion] does". If the total negative charge of all the electrons in earth material were uniformly distributed inside the Earth, and the same total positive charge were uniformly distributed over a volume of slightly smaller radius, the difference in radii would only need to be 10^‑10 cm to explain the dipole field.

Sutherland, W. "On the cause of the Earth's magnetism and gravitation", Terr. Mag. Atmos. Electr. 9 167-172 1904.

He now suggests that the electrostatic forces between positive and negative ions is different depending on whether they are in the same or different molecules. Differences of the order of 1 part in 10²² would explain both the geomagnetic field and gravity.

Sutherland, W. "Solar magnetic fields and the cause of terrestrial magnetism", Terr. Mag. Atmos. Electr. 13 155-158 1908.

That sunspots have large magnetic fields had just been discovered by Hale. Sutherland scales the magnetic field expression of his 1904 paper to a sunspot-sized rotating sphere of solar density, but finds the resultant fields a factor of 10-100 smaller than the observed ones. However, in a note immediately following the paper, Hale says that the observed value is lower than that used by Sutherland, and points out that the ionized solar plasma has a lot more available charge than an ionic solid, so that Sutherland's solar values were not unreasonable.

Swann, W.F.G., "The Earth's magnetic field", Phil. Mag. (6) 24 80-100 1912.

A detailed discussion of various types of fundamental rotation theories, and the way the effective current could vary with radius and angular velocity. To restrict the possibilities he uses the absence of significant magnetic fields for laboratory situations, and for the Sun. (He thought that 0.02 T was too small to be detectable by Zeeman splitting. Hale's measurement of 0.001 T had not yet been published.)

One of the possibilities was cylindrically radial polarization (which was taken up again later in a different form by Surdin in 1968-1979).

 

A footnote says that he became aware of Schuster's 1912 Presidential Address only "while the present paper was being written".

Swann, W.F.G., "Unsolved problems of cosmical physics", J. Franklin Inst. 195 No.4 433-474 1923.

A non-mathematical discussion of several topics, including the production of the Earth's magnetic field by various rotation theories.
"Presented at the Stated Meeting of the Institute held Wednesday December 20, 1922."

Swann, W.F.G., "A generalization of electrodynamics, consistent with restricted relativity and affording a possible explanation of the Earth's magnetic and gravitational fields, and the maintenance of the Earth's charge", Phil. Mag. (7) 3 No.18 1088-1136 1927.

"The generalized equations lead … in the case of a rotating neutral earth … to a fictitious current density". "The generalization replaces the term ru of classical electrodynamics by an infinite series containing all orders of time derivatives of the velocity [u]". He rejects a fictitious current density proportional to rw because it would presumably lead to measurable effects for linear motion of laboratory objects, and therefore chooses a variation proportional to r³w⁴. (Both types would give roughly the right ratio for the magnetic fields of the Sun and Earth.) If the constant of proportionality is chosen so as to give the correct field for the Earth, a 10 cm diameter sphere of density 5500 kg/m³ rotating at 100 rev/sec would then give a polar surface field of 17 nT.)

Surdin (1979) points out that choosing the factor r³w⁴ means introducing an arbitrary dimensioned constant.

Swann, W.F. & Longacre, A., "An attempt to detect a magnetic field as the result of the rotation of a copper sphere at high speed", J. Franklin Inst. 206 No.4 421-434 1928.

A copper sphere 10 cm radius was spun at up to 200 rev/sec about a vertical axis; the geomagnetic field was nulled (to about 1%) by a pair of Helmoltz coils. At first they tried an astatic magnetometer hanging symmetrically about the mid-plane of the sphere, but there was too much vibration. So they changed to using an astatic earth-inductor (a pair of coils spinning on a single shaft), connected by mercury slip-rings to AC amplifier, and AC galvanometer. On the theory of Swann (1927) the field produced by rotation at the magnetometer would have been up to 170 nT, but the observed field was no more than 10 nT.

Szarvassi, 1902.

Schlomka (1933) says Szarvassi produced a "rotation of surface negative charge" theory.

Thomson, J.J., "On the electricity of drops", Phil. Mag. (5) 37 341-358 1891.

The paper looks at the way drops become charged, and he is probably approaching the concept of ionic bonding. On the last page he has "positive electric tubes moving in a different way to the negative ones. … In the case of a rotating sphere the maximum force at the surface would be proportional to wa². If we take the Earth [as a measure of the effect], a sphere 1 foot (30 cm) in radius rotating 100 times a second would give a field not more than 10⁻⁸ that of the Earth's".

Thomson, W., See Kelvin, Lord

Trümper, J., Pietsch, W., Reppin, C., Sacco, B., Kendziorra, E. & Staubert, R., "Evidence for strong cyclotron emission in the hard x-ray spectrum of Her X-1", Annals of the New York Academy of Sciences 302 "Eighth Texas symposium on relativistic astrophysics" 538-544 1977

The most reasonable explanation of a strong line feature at 53 keV in the spectrum of the rotating neutron star/pulsar Hercules X-1 is that there is a 5x10⁸ T magnetic field at the poles.

Tzu, H.Y., "Universal constants in Blackett's formula", (Letter in) Nature 160 746-747 1947.

Argues that at least 3 linearly-independent fundamental quantities (G and c are two) would be needed to produce Blackett's theory from a general field theory. Therefore the constant b of Blackett's theory must contain at least one other quantity, and probably two. He suggests that some new physical principle must lie behind the formula.

von Bezold, 1893/95

Schlomka (1933) says von Bezold produced a "rotation of neutral material" theory.

Warwick, J.W., "The relation of angular momentum and magnetic fields: Schuster's hypothesis revisited", Phys. Earth Planet. Int. 4 229-232 1971.

Adds Jupiter to Blackett's 3-point graph. Corrects Blackett's assumption that the Sun was a rigid rotator of uniform density. (Blackett had overestimated angular momentum by a factor of 10.)

Wilson, H.A., "An experiment on the origin of the Earth's magnetic field", Proc. Roy.Soc. A 104 451-455 1923.

The paper is brief, and (to me) not very clear.

He introduces a "gravitational unit of mass" for which unit masses separated by unit distance give the same force as unit charges (cgsesu) at the same distance. He then suggests that unit mass "might be expected to produce a magnetic field of the same order of magnitude as the unit charge" [presumably when moving in the same way]. (Blackett 1947 says this can be interpreted as each element of mass having a volume charge density given by s(cgsesu) = G^0.5r(cgs).) For rotation this leads to an expression of the same form as Blackett's, and predicts the right order of magnitude of field for the Earth and Sun.

 

For reasons which I do not understand, he tried to measure the magnetic flux changes in an iron toroid spinning about a diameter at the Earth's surface, but there was too much noise. He then changed to (approximately) linear motion, looking for any flux changes in a test cylindrical iron bar which was the bob of a pendulum, swinging in a plane perpendicular to the cylinder axis. His theory predicted an effective field of 1000 nT, but he claimed to have detected less than 1/5000 of that. (Barnett (1949) argues that Wilson would only have seen his magnetic field if the magnetometer were exposed to the electric field of the charges, but that the conducting walls of the charges would have screened it.)

 

This experiment is often quoted as showing the absence of any significant effect of linear motion. But my own interpretation of his account(and colleagues agree) is that all he did was to change the local magnetic field gradient (presumably to approximately zero) until no flux change was observed, so I do not see what it was he thought he was measuring!