1876 Helmholtz

A report of Rowland's experiment (which was carried out in Helmholtz' laboratory).

 

See Rowland (1878).

1878 Rowland

The first experiment to demonstrate that rotating electrostatic charge produced magnetic field.

1879 Perry & Ayrton

Suggested that rotation of real surface charge on the Earth's surface could produce the dipole field. But there is a mistake in their calculation, see Rowland, (1879.)

1879 Rowland

Corrects the calculation of Perry & Ayrton, and shows that the resulting external electric field would be enormous.

1891 Thomson, J.J.

In the context of the electrification of drops, at the end suggests an effect (unspecified, but possibly equivalent to electric polarization at the molecular level) which would lead to a rotating body being magnetic.

1891 Schuster

Points out that the form of the solar corona suggests that the Sun has a dipole magnetic field. He goes on to make the first suggestion that there might be some "fundamental rotation theory" for the Earth's magnetic field.

1892 Kelvin

"I find it unimaginable but that terrestrial magnetism is due to the greatness and rotation of the earth", but no theory is suggested.

1893 Schuster

Simply poses the question "Is every large rotating mass a magnet?", but no theory is suggested.

1893 von Bezold

Schlomka, l933, says von Bezold produced a "rotation of neutral material" theory.

1900 Sutherland

The first explicit suggestion that having two charge densities of opposite sign at different radii, rotating with the Earth, would avoid the problem of very large electrostatic fields in the atmosphere. He suggests that it is not unreasonable that a solid dielectric could withstand the resultant very large internal fields.

1902 Szarvassi

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

1903 Arrhenius

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

1903 Sutherland

Introduces the concept of the total (electron) negative charge of earth material being uniformly distributed throughout a slightly larger sphere than is the equivalent positive charge. A difference of radius of 10⁻¹⁰ cm would be sufficient to explain the dipole field. Referring to Thomson (1891), he suggests that the charge separation could be a small-scale polarization of ionic crystals.

1904 Sutherland

Adds the suggestion that making the forces between positive and negative ions very slightly different, depending on whether they are in the same or different molecules, could also give the gravitational field, as well as the magnetic field of rotating bodies.

1905 Pflüger

Schlomka (l933) says Pflüger produced a "rotation of surface negative charge" theory.

1908 Sutherland

The magnetic fields of sunspot had just been discovered by Hale. Sutherland tried to scale up his 1904 expression to a sunspot-sized rotating sphere of solar density. He did not think the resulting value was large enough.

 

But see Hale (1908).

1908 Hale

Pointed out some mistakes in the solar values Sutherland (1908) had used; the effect was to make Sutherland's scaling more reasonable.

1912 Lébedèw

Rotated small toroidal rings of various materials at speeds up to 500 rev/sec; could detect no field greater than 100 nT, though he was expecting fields of 10,000 nT.

1912 Schuster

A broad review. Produces an expression equivalent to Blackett's formula. But points out that his simple theory would predict large effects for linear motion. He also points out that while an observer moving with the Earth would see the same vertical field as a stationary observer, such a moving observer would see a quite different horizontal field.

 

He did not know of Hale's measurement of the solar field.

1912 Swann

Another broad review, written independently of Schuster's. Uses various arguments to restrict the sorts of theory which are feasible.

 

He did not know of Hale's measurement of the solar field.

1912-13 Bauer

Various suggestions as to how the non-dipole part of the Earth's field could be produced by modifying rotation theories.

1912-13 Hale

The first measurement of the general magnetic field of the Sun.

1914 Brunt

Discusses the limitations of various theories.

1922 Décombe

Schlomka (l933) says Décombe produced a "rotation of quasi-charge, or quasi current" theory.

1923 Swann

A non-mathematical discussion.

1923 Wilson

Cited as being the first, and only, experimental confirmation that linear (as opposed to rotational) motion with respect to the Earth gave no measurable magnetic field. The description of the experiment is very poor, but I (F.J.L.) and colleagues do not think the experiment is valid!

1924 Einstein

Schlomka (l933) says Einstein produced a "rotation of quasi-charge, or quasi-current" theory.

1925 Angenheister

Suggests a (fictitious) negative volume charge density proportional to mass density, with positive surface charge to make the body electrically neutral. When rotated this gives a dipole magnetic field. The ratio of required electric to mass density is the same for the Sun and Earth; this is equivalent to Blackett's formula.

1927 Swann

A detailed discussion of possible forms of (fictitious) current densities coming from "fundamental rotation" theories.

1928 Swann & Longacre

An experiment to show that a spinning copper sphere gave less than 10% of the field expected on the (then) most reasonable fundamental rotation theory.

1929 Chapman

Argues against there being a fundamental rotation theory.

1929 Haalck

A charge separation theory.

 

Criticized by Schlomka (1932).

1932 Schlomka

Criticizes Haalk (1929)

1933 Schlomka

Suggests that if the repulsion between electron/electron and proton/proton was different from the attraction between electron/proton, rotation of the resultant charge separation would lead to a magnetic dipole moment.

1936 Haalck

More charge-separation theory.

 

Criticized by Schlomk (1937).

1937 Schlomka

Criticizes Haalck (1936) because of the very large internal electric fields which would be produced.

1937-38 Haalk

These two papers attempt to apply the idea of charge separation produced by a pressure gradient to the hot interiors of the Earth and Sun.

1938-47 Mariani

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.)

1940 Chapman & Bartels

Chapter 21 of this classical textbook has a useful summary of much of the previous work.

1947 Barnóthy

(Pseudo-) Charge is associated with protons and neutrons.
See Cowling (1947).
Although published after Blackett (1947), this paper was not influenced by Blackett.

1947 Cowling

A criticism of Barnóthy (1947)

1947a Babcock

The first measurement of the magnetic field of a star.
It was this measurement, of 78 Virginis, which triggered Blackett's interest.

1947b Babcock

"It is noteworthy, though perhaps fortuitous, that … the magnetic dipole moment of each body [Earth, Sun, 78 Virginis] is proportional to its angular momentum." Several other stars of the same stellar class had magnetic fields of the same magnitude.
He refers to the earlier work of Swann, Swann & Longacre, and Schlomka, but does not know of Blackett's paper.
"Received April 30, 1947. Read at the June meeting of the Society."

1947 Blackett

His 15^th May 1947 R.S. talk at which, using the magnetic fields of Earth, Sun, and 78-Virginis, 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; this led to the "Blacket formula" (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. Contains a comprehensive review of earlier theories.

At the meeting, Bullard suggested measuring the variation of field with depth inside the Earth as a test to distinguish between (one interpretation of) a "fundamental", or "distributed", theory, and a "core" theory, of the origin of the geomagnetic field.

1947 Chapman

Blackett's formula would give a significant field on the Moon; he suggested sending a rocket.

1947 Hales & Gough

The results of measuring the variation of field with depth down a coal mine in South Africa. The results appeared to favour a "distributed" theory. (But it was later realized that the results were strongly affected by the magnetic rocks of the region.)

 

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

1947-48 Giao

The first of many attempts to produce a theoretical backing for Blackett's empirical formula.

 

The first of these papers was presented to the Academie des Sciences de Paris only 6 weeks after Blackett's talk.

1947 Tzu

More theory.

1948 Barnett

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).

1948a Chapman

Points out a mistake in the Runcorn-derived formula (for field variation with depth) used by Hales & Gough (1947).

1948 Runcorn

Reply to Chapman.

1948 Runcorn

More detailed calculation of field variation with depth.

1948b Chapman

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

1948c Chapman

Thorough calculation of internal and external fields given by a current density proportional to mass motion.

1948d Chapman

Report of RAS Geophysical Discussion of 27 Feb 1948, in which Runcorn reported on Hales & Gough (1947), and gave a preliminary account of the 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!.

1948e Chapman

Gives general expression for calculating magnetic field inside spherically symmetric rotating body.

1948 Arley

Theoretical work on Blackett's formula.

1948 Fuchs

Argues for a more general expression of the Blackett equation.

1948 Piaggio

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 1938-1947.

 

Published Mar 20.

1948 Mariani Submitted 12 Nov 1947, published Jan 1948.

Suggests a theoretical basis for Blackett's formula based on rotating fictitious charge.

He does not refer to his own earlier papers!

1948 Pliner

 

1948 Salceanu

More theory.

1948 Procopiu

 

1949 Benfield

Suggests that there might be a very small effect due to the separation of (real) charge in the radial pressure gradient.

1949 Anonymous (cited as Blackett by some authors)

 

1949 Gold

These are two reports of the RAS Geophysical discussion of 25 February 1949.

 

Runcorn talked about the mine experiment, (no clear results yet), Blackett suggested an experiment with a massive object stationary in the laboratory (see Blackett 1952), and Gold discussed various theoretical aspects.
(B.C.Browne reported Bullard's early work on dynamo theory).

1949a Blackett

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

1949b Blackett

 

1949 Caussé,

A theory based on kinematic relativity, applied to Earth and Sun.

But see Milne (1950).

1950 Milne

Claims Caussé is wrong, then produces his own theory based on kinematic relativity, but only for galaxies.

 

But see Gething (1952).

1950 Berlage

Suggests the radial separation of (real) charge in celestial bodies. The net charge is now zero, so there is no electric field outside the body.

But see Benfield (1950).

1950 Benfield

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

1950 Runcorn et al.

Report of the experiment to measure the variation of field with depth at three coal mines. The results favoured a "core" theory.

1950 Papapetrou

More theory.

But see Luchak, 1951a.

1951a Luchak

Criticism of Papapetrou (1950).

1951b Luchak

More theory.

1951 Runcorn et al.

Full report of measurements at five mines. The results favoured a "core" theory.

1951 Neugebauer

Pressure induced charge separation.

1952 Blackett

(He had decided that the direct test (of his formula) of measuring the field from a rotating cylinder was too difficult.)

 

He describes the design and construction of an optimized astatic magnetometer. On a not unreasonable interpretation of the theory (but see Surdin 1977), a static 10 cm gold cylinder would be expected to give a field of 10⁻¹² T near it, but any observed field was less than 10% of this.

(This magnetometer was then used to measure rock samples, and was a major contributor to the rebirth of palaeomagnetism in the UK.)

1952 Gething

Questions Milne's (1950) claim to have established a theoretical basis for Blackett's formula.

1952 Holm

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

1953 Arley et al.

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

1954 Darwin

Decelleration of the Earth's rotation would give trivial effect from electron inertia.

1956 Esperson et al.

The detailed report of the 1950-52 Galathea attempt to measure the variation of the magnetic field with depth in the ocean. A noise level of 10-20 nT was achieved by the end, but unfortunately only in places where there were large crustal gradients.

1967 Cranna & Papini

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

1968 Moore & Kuhlmann-Wiksdorf

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

1968 Surdin

 

1971 Surdin

In 1979 he says "universal fluctuations of the electromagnetic field" induce cylindrically-radial electric polarization in rotating bodies, giving a magnetic field which reverses spontaneously. For the field magnitude he deduces an expression equivalent to Blackett's formula.

 

(Very dubious theory!)

1971 Warwick

Adds Jupiter to Blackett's 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.)

1972 Atanasov

I suspect this is not relevant.

1973 Kumar & Nandini

More theory, but only for an infinite cylinder.
The authors do not refer to any of the other papers on the subject.

1977 Surdin

Points out that on his theory the field decreases towards the surface, so was not disproved by the mine experiment. Also disputes the interpretation Blackett used for the static-mass experiment, and says Blackett's result (for 30-second average field) was irrelevant.
Gives an account of an experiment the results of which he claims agrees with the predictions of his theory.

1977 Juergans

"On the convection of electric charge by the rotation of the Earth". Supports Velikovsky by suggesting an "interplanetary bolt" from a plasma sheath to reverse the magnetic field!

1977 Trümper et al.

The rotating neutron star/pulsar Hercules X-1 probably has a magnetic field of about 5x10⁸ T.

1978 Ahluwalia & Wu

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

1979 Surdin

Gives a clearer picture of what his theory involves. Adds the planets, neutron star, and a galaxy to his comparisons.

1979 Sirag

Adds the magnetic field of the pulsar Hercules X-1 to give a fourth point on the Blackett diagram (but ignores the, by then, known reversals of the magnetic field of the Earth and stars). Argues that Blackett's (negative) interpretation of the mine and (static gold cylinder) laboratory experiments was wrong, and urges direct experiment using a massive rotator.)

1980 De Sabbata & Gasperini

More theory.

1983 Kuznetsov

"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 separated charges then explains the production of the field (and many other phenomena).

Very dubious!

1983 Shrivastava

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.

Date unknown Eichenwald

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", but does not give a direct reference.