A.D. 1803.—Biot (Jean Baptiste), who, in 1800, at the age of twenty-six, was made Professor of Natural Philosophy at the “Collège de France,” and afterward ranked among the first astronomers and mathematicians, gives an account of his journey to Aigle, in the Department of l’Orne, whither he was sent by the Government to examine and report upon a very extraordinary shower of meteorites. The facts obtained by him were communicated to the Institute on the 29th Messidor, An. XI, and also appeared at the time in the Paris Journal des Débats (Phil. Mag., Vol. XVI. p. 299).
On the 23rd of August of the year following (1804) Biot accompanied Gay-Lussac in the latter’s first memorable balloon ascent. This aeronautic voyage, sanctioned by the French Government mainly through the efforts of Berthollet and Laplace, was the first of the kind undertaken solely for a scientific object.
Besides numerous barometers and electrometers, Biot and Gay-Lussac carried with them two compasses, a dipping needle and other instruments. For the examination of the electricity of different strata of the atmosphere, they had several metallic wires from 60 to 300 feet in length, also a small electrophorus feebly charged, while for galvanic experiments they added some discs of copper and zinc, together with a supply of frogs, insects and birds. An account of the exceedingly important results obtained by those scientists at different elevations, of which the highest reached exceeded four miles, was read before the National Institute, Aug. 27, 1804. It was also published in London during the latter year, and alluded to at p. 371, Vol. XIX of the Philosophical Magazine. Mary Somerville remarks (“Connection of the Physical Sciences,” 1846, p. 334) that according to the observations of Biot and Gay-Lussac, the magnetic action is not confined to the surface of the earth, but extends into space. The moon has become highly magnetic by induction, in consequence of her proximity to the earth, and because her greatest diameter always points toward it. Her influence on terrestrial magnetism is now ascertained; the magnetism of the hemisphere that is turned toward the earth attracts the pole of our needles that is turned toward the south and increases the magnetism of our hemisphere; and as the magnetic, like the gravitating force, extends through space, the induction of the sun, moon and planets must occasion perpetual variations in the intensity of terrestrial magnetism, by the continual changes in their relative positions.
In 1805 Biot published an investigation of the laws which should govern the dip and intensity, in the hypothesis of a magnet situated at the centre of the earth, having its poles infinitely close to each other and directed to opposite points on the surface of the globe and, as justly adds Major Edward Sabine (Report Seventh Meeting Brit. Asso.), it is a well-known consequence of this hypothesis that the lines of equal dip and equal intensity on the earth’s surface should everywhere be parallel to each other. The phenomena of electricity had been brought within the pale of mixed mathematics by C. A. Coulomb (A.D. 1785), whose considerations mainly attached to the distribution of electricity upon the surface of spheres, and his investigations were at once diligently pursued by the French scientists, Biot, Laplace and Poisson. Laplace, who undertook to investigate the distribution of electricity upon the surface of ellipsoids of revolution, showed that the thickness of the coating of the fluid at the pole was to its thickness at the equator as the equatorial is to the polar diameter, or, what is the same thing, that the repulsive force of the fluid, or its tension at the pole, is to that at the equator as the polar is to the equatorial axis. Biot extended this investigation to all spheroids differing little from a sphere, whatever may be the irregularity of their figure, and his solution of the problem will be found in No. 51 of the Bulletin des Sciences. He also determined, analytically, that the losses of electricity form a geometrical progression when the two surfaces of a jar or plate of coated glass are discharged by successive contacts, and he found that the same law regulated the discharge when a series of jars or plates are placed in communication with each other (Whewell, “History of the Inductive Sciences,” Vol. II. pp. 208, 223; Noad’s “Manual,” p. 15; Eighth “Britannica,” Vol. VIII. p. 531. For Biot’s experiments, touching upon electrical attraction and demonstrating practically the distribution of electricity upon the surface of a conductor, see the last-named volume of the “Britannica,” pp. 552, 556, and Noad, p. 56).
In conjunction with Frederick Cuvier, Mr. Biot investigated the connection of chemical charge with the production of electricity. Like Mr. W. H. Pepys, they examined the effect produced by the pile on the atmosphere in which it is located. Mr. Pepys placed the pile in an atmosphere of oxygen, and found that in the course of a night 200 cubic inches of the gas had been absorbed, but that in an atmosphere of azote the pile ceased to act. Biot and Cuvier likewise observed the quantity of oxygen absorbed, and inferred from their experiments that “although, strictly speaking, the evolution of electricity in the pile was produced by oxidation, the share which this had in producing the effects of the instrument bore no comparison with that which was due to the contact of the metals, the extremity of the series being in communication with the ground.” Their investigation was attended by the discovery that as long as any oxygen remained to be absorbed, the chemical and physiological effects of the apparatus still continued, but with decreasing intensity; so that if the conducting wires attached to the two poles are made to return from under the receiver in tubes of glass they may be used to decompose water and communicate shocks to the organs. All these effects, however, cease when the surrounding oxygen is exhausted (Annales de Chimie, Vol. XXXIX. p. 242; Soc. Philomathique, An. IX. p. 40; Sue, “Histoire du Galv.,” Vol. II. p. 161).
In the second volume of Biot’s “Traité de Physique” will be found recorded his many observations on the nature and origin of the electric light, extracts from which are given by Sir David Brewster in the electricity article of the “Britannica.” Biot remarks that the light which is observed during an electric explosion was for a long time considered by philosophers as a modification of the electric principle itself, which they supposed to be the quality of becoming luminous at a certain degree of accumulation (John Farrar, “Elem. of Elec., Mag. and El. Mag.,” 1826, p. 118). Brewster adds that this eminent French writer, however, considered the opinion as erroneous, and he has devoted a whole chapter to prove that electricity has the same origin as the light disengaged from air by mechanical pressure, “and that it is purely the effect of the compression produced on the air by the explosion of electricity.” In order to establish this theory, Mr. Biot has stated, on the authority of several experiments, “that the intensity of electric light depends always on the ratio which exists between the quantity of electricity transmitted and the resistance of the medium”; and he has shown, by an experiment with Kinnersley’s thermometer, “that at each spark the air of the cylinder, driven by the repulsive force, presses on the surface of mercury, which rises suddenly in the small tube, and falls back again immediately after the explosion.” He adds:
“This indication proves the separation produced between the particles of the mass of air where the electricity passes; and from what we know of its extreme velocity it is certain that the particles exposed immediately to its shock ought in the first moment to sustain individually all the effect of the compression. They ought, then, from this cause alone to disengage light, as when they are subjected to any other mechanical pressure. Thus one part at least of the electric light is necessarily due to this cause; and this being the case, there is no experiment which can lead us to conjecture that it is not all due to this cause.”
References.—“Encycl. Brit.,” 1857, Vol. XIV. pp. 7, 63, and Journal de Physique, Vol. LIX. p. 450. For Mr. Biot’s observations on the magnetism of metals and minerals, and on the distribution of magnetism in artificial magnets, as well as for his improvement upon Coulomb’s method of constructing the latter, see the last-named volume of the “Britannica,” pp. 23, 26, 71, and Noad’s “Manual of Electricity,” London, 1859, pp. 528, 535, while, for Biot’s very ingenious theory relative to the aurora, see Lardner and Walker’s “Manual of Elec. Mag. and Meteor.,” London, 1844, Vol. II. p. 235, and Noad, pp. 232, 233. The observations concerning the laws regulating the intensity of electro-magnetic phenomena, made by MM. Biot and Savary, are alluded to by Noad at pp. 644, 645, in the “Encycl. Metropol.” (Elec. Magn.), Vol. IV. p. 427; and Whewell’s “History of the Inductive Sciences,” 1859, Vol. II. pp. 245–249; “Scientific papers of the Royal Society,” Vol. I. pp. 374–386; Biot’s “Traité de Phys. Exp. et Math.,” Vol. II. p. 457; Journal de Physique, Vol. LIX. pp. 315, 318; Wilkinson’s “Elem. of Galv.,” Vol. II. pp. 38, 123, 154, 361, Chap. XVI; Humboldt’s “Cosmos,” treating of Aerolites, of the Zodiacal Light and of the figure of the earth; Noad, “Manual,” p. 530; Eighth “Ency. Brit.,” Vol. VIII. p. 580; Sir H. Davy, “Bakerian Lectures,” London, 1840, p. 3, alluding to Biot and Thénard in No. 40 of the Moniteur for 1806; “Encycl. Metropol.,” Vol. IV. (Electro-Magn.), p. 7; Harris “Rudim. Magn.,” Part III, London, 1852, pp. 116, 117; Gautherot at A.D. 1801; Figuier, “Exposition,” etc., Paris, 1857, Vol. iv. p. 429; “Lib. of Useful Knowl.” (Electricity), p. 64 and (Magnetism), p. 89; “Soc. Philomath.,” An. IX. p. 45; An. XI. pp. 120, 129; Becquerel’s “Traité,” 1856, Vol. III. p. 11; Phil. Mag., Vols. XVI. p. 224; XXI. p. 362; “Mém. de l’Institut” for 1802, Vol. V; “Annales des Mines” for 1820, relative to the experiments on electro-magnetism made by Oersted, Arago, Ampère and Biot; Phil. Mag., Vol. XXII. pp. 248, 249, for the magnetical observations made by Biot and Arago; Comptes Rendus for 1839, I Sem., VIII, No. 7, p. 233, for the observations of Biot and Becquerel on the nature of the radiation emanating from the electric spark; “Chemical News,” London, 1868, Vol. XVI for John Tyndall’s lecture on some experiments of Faraday, Biot and Savary; “Atti dell’ Accad. dei Nuovi Lincei, Ann.,” XV. Sess., IV. del 2 Marzo 1862, for the biography of J. B. Biot, who died Feb. 2, 1862, within two months of the completion of his eighty-eighth year. “Journal des Savants” for June and July 1820, April 1821, and for Feb.-Mar.-April 1846.
J. B. Biot’s son, Edward Constant Biot (1803–1850), is the author of the extended catalogue of shooting stars and other meteors observed in China during twenty-four centuries, which was presented to the French Academy during 1841, and a supplement to which was published at Paris in 1848 (Acad. des Sciences, Savants Etrangers, Tome X).
A.D. 1803–1805.—Acting upon the discovery of Gautherot, the Bavarian philosopher Johann Wilhelm Ritter (1776–1810) is the first to construct an electrical accumulator.