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sort of temporary magnetism might have been more reasonable. But Ampère had himself already been looking for a possible inductive effect ; nor was he alone in the idea that such might exist. Fresnel bad on November 6th, 1820, announced to the Academy of Sciences that he had decomposed water by means of a magnet which was laid motionless within a spiral of wire. Emboldened by this announcement, Ampère remarked that he too had noticed something in the way of production of currents from a magnet. But before the end of the year these statements were withdrawn by their authors. Fresnel wrote * to the Annales de Chimie explaining the matter. He had surrounded a bar-magnet of steel with a spiral of iron wire, the ends of which dipped into water; and what he had announced on November 6th was that he had found one end of the iron wire to be discoloured and oxidized, while the other became covered with minute bubbles. He now finds that the announcement was premature, that the effects were not sustained by repeating the experiment, and, further, he says he does not believe in the success of Ritter's much earlier attempts to decompose water by a magnet. On behalf of M. Ampère, he added that the latter had indeed found little movements of a magnetic needle by bringing near it a circuit of copper wire (laiton) of which a portion was coiled in a spiral around a magnet, but that these movements were not repeated in any constant manner. Further, that these movements were, moreover, so feeble that Ampère would not have published the experiments if the success of Fresnel's, which he thought certain, had not persuaded him that these small agitations were occasioned also by an electric current resulting from the action of the magnet on the spiral in which it was enveloped.

This having occurred in 1820, it is clear that when making the Geneva experiment in 1822 Ampère must have had before him the possibility of induced currents, and chose rather the explanation of a temporary magnetism conferred on the copper loop.

Others in the meantime had tried to repeat Fresnel's observation, and found it erroneous.

Gilbert t, after giving an abstract of Fresnel's reputed discovery, says that he repeated the experiment without finding any discoloration of the iron wire, and concluded that the announcement was premature. Similar conclusions were arrived at by Pohl*.

* Ann. Chim. Phys. xv. 1820, pp. 219-222," Note sur des Essais ayant pour but de décomposer l'eau avec un aimant."

+ Gilb. Ann. xlvi. p. 410.

A year or two later, when Arago's rotations were attracting the attention of experimenters, Becquerel † investigated the supposed magnetism of bodies by taking small pieces of them, which he hung within a multiplier-coil of wire in place of the usual magnetic needle, and then turning on a current observed whether they moved or not. He found signs of magnetic action in needles made of peroxide of iron, copper, wood, and even shellac. After narrating his own experiments, he alluded to the Geneva experiment of Ampère, on p. 272, in the following terms :

“Il résulterait de cette expérience, vu l'action semblable exercée par les deux poles de l'aimant en fer à cheval sur une même portion du circuit, que l'influence du courant électrique aurait développé dans la lame un autre courant électrique, tel qu'on en observe dans un fil métallique qui communique avec les deux poles d'une pile voltaique ; mais M. Ampère s'est assuré depuis qu'il n'en est pas ainsi.” What steps Ampère had in the meantime taken to assure himself that induction currents did not exist, Becquerel did not state, however.

In 1831 came Faraday's discoveries of the induction of currents by magnets, of the induction of currents by other currents, and of the cause of Arago's rotations. A group of notes on these discoveries is to be found in December 1831 in the Annales de Chimie. It is curious to note the change of views. Becquerel and Ampère's communication to the Academy of January 23, 1832, appears along with abstracts of Faraday's work, and with an account of the experiments of Nobili and Antinori. There is an epitome of facts observed by Becquerel, and another of things to be looked for, by Ampère. This is followed by the following :-“Expériences sur les Courans électriques produits par l'influence d'un autre Courant,” par M. Ampère. This article gives a third version of the Geneva experiments.

“ Pendant mon séjour à Genève au mois de septembre 1822, M. Auguste de la Rive voulut bien m'aider dans des expériences que je désirais de faire sur la production d'un courant électrique par l'influence d'un autre courant. ... Nous présentions à ce cercle un fort aimant en fer à cheval, de manière qu'un de ses poles se trouvait au dedans et l'autre ar dehors du cercle. Dès que nous faisions communiquer avec la pile les deux extrémités du fil conducteur le cercle était attiré ou repoussé par l'aimant, suivant le pole qui répondait à l'intérieur du cercle : ce qui démontrait l'existence du courant électrique qui y était produit par l'influence du courant du fil conducteur. La découverte que vient de faire M. Faraday des courans électriques produits par l'influence d'un aimant, courans qu'avait obtenu Fresnel en 1820, mais qu'il n'avait pas cru suffisamment constatés par ses expériences, m'a porté naturellement à employer le galvanoscope multiplicateur, dont l'illusire chimiste anglais a fait usage, pour constater de nouveau et étudier dans toutes ses circonstances la production d'un courant électrique par un autre courant.'

* Oken's Isis, 1822, pt. iv. p. 407. Also see remarks signed “P” at the end of an article by Savary in Pogg. Ann. viii. p. 368 (1826).

Ann. Chim. Phys, xxv. p. 269. † Ann. Chim. Phys. xlviii

. 1831, pp. 405-428 ; see also Pogg. Ann. xxiv, 1832, p. 612, and particularly p. 614.

Ampère seems to have considered that the oxidation at first alleged by Fresnel was caused by induction currents arising from the diurnal variations of the magnetism of the stationary magnet. But it is evident that the electromotive forces due to any such cause would be of an order of magnitude utterly inadequate for the purpose. Further, as such currents must necessarily have been in alternate directions during the rise and fall of temperature, the total chemical action at the end would in no way depend upon the intermediate charges, but only upon the difference between the initial and final temperatures. Hence the total electromotive impulse tending to chemical action must have been infinitesimal compared with that due to simply removing the magnet once from the circuit! The third version differs from the former in describing the position of the magnet, and saying that the magnet (which in the original Ampère experiment was brought up after the current had been turned on) was placed in position before the circuit was completed.

From that time forward Ampère's experiment seems to have passed into oblivion. One reference to it, however, appeared in 1872, which gives a fourth version, differing not only from the three former, but accompanied by a picture and description of a very different form of apparatus. This description, from the

pen of the usually accurate M. Verdet, is to be found at p. 357 of his well-known Conférences de Physique. It runs as follows :

“ 209. Expérience d'Ampère et De la Rive. -Longtemps avant l'époque où Faraday fit la découverte de l'induction, Ampère et De la Rive * avaient fait une expérience relative

Bibliothèque Universelle, septembre 1822, et Annales de Chimie et de Physique [2], t. xxi. p. 47 (1822), et t. xxv. p. 272 (1824).

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à ces phénomènes et qu'ils n'avaient pas comprise. Ces physiciens cherchaient s'il y avait une action des courants sur des conducteurs places à distance, par analogie avec les effets d'influence de l'électricité ordinaire ; ils entreprirent une série d'expériences avec l'idée préconçue que le phénomène produit par le passage du courant dans un conducteur voisin serait permanent, c'est à dire persisterait pendant tout le temps que le courant traverserait le conducteur ; ayant au contraire observé un phénomène instantané, ils regardèrent ce résultat comme un fait singulier ne méritant pas une étude ultérieure. Voici en qui consistait leur expérience : un fil fin de cuivre enroulé en anneau A (fig. 2) était suspendu à un fil de soie

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sans torsion OC, devant la base d'un électro-aimant BB', de manière que les plans des spires de l'electro-aimant fussent parallèles au plan de l'anneau. A l'instant où le courant était lancé dans l'électro-aimant, l'anneau était repoussé ; mais cette déviation ne persistait pas, et bientôt le fil revenait rigoureusement à la verticale. Si l'on interrompait le courant, on observait une attraction aussi peu persistante que la répulsion.”

The anachronism of representing a soft-iron electromagnet as having been used in 1822 is the strangest part of this description. But the experiment, as described by Verdet, is of interest as being a sort of forerunner of the actions observed in 1884 by Boys *, and in 1887 by Elihu Thomson.

I have repeated the experiment of Ampère in the form originally shown to De la Rive. It is quite easy

of

performance : but the relatively great moment of inertia of the copper circle masks the purely transitory effect of the impulse which the ring receives each time the current is turned on or off in the outer coil.

* “ A Magneto-electric Phenomenon.” Proc. Phys. Soc. vol. vi. p. 218, 1884; Phil. Mag. [5] xviii. p. 216.

Phil. May. S. 5. Vol. 39. No. 241. June 1895.

20

LIV. Proceedings of Learned Societies.

GEOLOGICAL SOCIETY.

[Continued from p. 142.] November 21st, 1894.-Dr. Henry Woodward, F.R.S., President,

in the Chair. THE 'HE following communications were read :

1. The Pleistocene Beds of the Maltese Islands.' By John H. Cooke, Esq., F.L.S., F.G.S.

For the right understanding of the Pleistocene beds, a previous knowledge of the physiography of the islands and of the earlier sediments is necessary.

A full description of the physiography and of the character of the sediments, so far as they are necessary for the understanding of the accumulations forming the subject of the paper, occupies its earlier portion. Especially noticeable is the absence of ordinary anticlinal and synclinal folding, and the predominance of monoclinal faults, which largely affect the character of the surface. These faults were formed prior to the deposition of · the Pleistocene beds.

The plateaux of Malta, rising to a height of 600–800 feet above sea-level, occur south of the great east-and-west fault, which has a downthrow to the north. They have no Pleistocene deposits upon their summits.

Three classes of superficial deposits are described :

I. Valley-deposits, including (a) those found on the higher slopes of plains and plateaux, due to subaërial waste and rain-action, containing land-shells and mammalian bones; and (b) those situated at the bottoms of valleys, consisting of stratified layers of waterworn sand, gravel, and large pebbles, occurring in such order as to show that the agents which produced them have greatly decreased in intensity.

II. Agglomerates and breccias found along coast-lines and faultterraces, always at the foot of the fault-terraces, or along the lower slopes of the depressed areas: these accumulations are either submerged or lie at the water-line. Their materials are much waterworn, and land-shells are contained in many of the layers. The agglomerates are in many cases distinctly stratified; and the author concludes that the materials appear to have been swept down, during heavy rainfall, into the waters of land-locked creeks.

III. Ossiferous deposits of caves and fissures, which have been described elsewhere.

2. Geological Notes of a Journey in Madagascar.' By the Rev. R. Baron, F.L.S., F.G.S.

The part of the island travelled over may be divided into four sections.

I. Antananarivo to the East Coast.—The principal rock is a hornblende granitite-gneiss, but there is also much norite usually containing olivine. The general strike of gneiss and norite along this

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