Chapter XXXVI: Part XV: , xxxviii; Vol. VIII, first part, p. 361; Reply to Mr. W (2)

Mr. Taylor justly adds that subsequent experiments have proved Ohm’s law (announced three years after Barlow’s) of a simple ratio of resistance to length as approximately correct.

REFERENCES.--G. B. Prescott, “The Speaking Telephone,” 1879,
II; _Sci. Am. Supp._, Nos. 405, p. 6466; 453, p. 7235; 547, p.
8735: “Mem. of Jos. Henry,” 1880, pp. 83, 94, 144, 485, 487.
See also, Poggendorff, Vol. I. pp. 102, 103; Whewell, “Hist.
Ind. Sciences,” 1859, Vol. II. pp. 223, 224, 245, 254, 616;
“Lib. Useful Knowledge” (Magnetism), p. 86 and (El. Mag.), pp.
7, 18, 22, 28; Sturgeon’s “Sci. Researches,” Bury, 1850, pp.
26, 29, 31, 298; Humboldt, “Cosmos,” 1849, Vol. I. p. 183; Mrs.
Somerville, “On the Earth not a Real Magnet,” in the “Conn. of
the Phys. Sci.,”; _Phil. Mag._, Vols. LV. p. 446; LX. pp. 241,
343; LXII. p. 321; Harris, “Rud. Mag.,” Part III. pp. 114–116;
“Encycl. Metropol.,” Vol. IV (Elect. Mag.), pp. 1–40; “Abstracts
of papers ... Roy. Soc.,” Vol. II. pp. 164, 197, 241, 318; “Cat.
Sc. Papers ... Roy. Soc.,” Vol. I. pp. 182–184; “Bibl. Britan.,”
Vol. XX, N.S. p. 127; “Edin. Phil. Journal,” 1824, Vol. X. p.
184 (alludes to papers of Barlow and Christie in _Phil. Trans._
for 1823, Part II).

Mr. Wm. Henry Barlow, second son of Peter Barlow, is the author of a treatise, “On the spontaneous electrical currents observed in the wires of the electric telegraph,” which was published in London during 1849 and appeared in Part I of the _Phil. Trans._, for that year. He is also the inventor of a new electrical machine alluded to herein at Hare (A.D. 1819), also at p. 130 of the “Annual of Sc. Disc.,” at pp. 76–77 of Noad’s “Manual,” and at p. 428, Vol. XXXVII of the “Philosophical Magazine.”

=A.D. 1820.=--Laplace (Pierre Simon, Marquis de) (1749–1827), a very distinguished French astronomer and mathematician, suggests for telegraphic purposes the employment of magnetic needles suspended in multipliers of wire, in place of the voltameters of Sömmering, and on the 2nd of October 1820 his theory is thus explained by Ampère in a paper read before the French Academy of Sciences:

“According to the success of the experiment to which Laplace drew my attention, one could, by means of as many pairs of live wires and magnetic needles as there are letters of the alphabet, and by placing each letter on a separate needle, establish, by the aid of a distant pile, and which could be made to communicate by its two extremities with those of each pair of conductors, a sort of telegraph, which would be capable of indicating all the details that one would wish to transmit through any number of obstacles to a distant observer. By adapting to the battery a keyboard whose keys were each marked with the same letters and establishing connection (with the various wires) by their depression, this means of correspondence could be established with great facility, and would only occupy the time necessary for pressing down the keys at the one station and to read off the letters from the deflected needles at the other.”

Laplace is, perhaps, best known by his “Traité de Mécanique Céleste,” the sixteen books and supplements to which are by many considered, next to Newton’s “Principia,” the greatest of astronomical works; a book which has been truly said to have had no predecessor and which has been called the crowning glory of Laplace’s scientific career. His next important work was the “Théorie Analytique des Probabilités,” the most mathematically profound treatise on the subject which had yet appeared, while his “Système du Monde” was called by Arago “one of the most perfect monuments of the French language.” By Prof. Nichols, Laplace is called “the titanic geometer”; by Mr. Airy “the greatest mathematician of the past age”; by Prof. Forbes “a sort of exemplar or type of the highest class of mathematical natural philosophers of this, or rather the immediately preceding age.”

Laplace also wrote, in conjunction with Lavoisier, a treatise “On the Electricity which Bodies Absorb when Reduced to Vapor” (_Mém. de Paris_ for 1781). Prof. Denison Olmstead, treating of the origin of atmospherical electricity (“Introd. to Nat. Phil.,” 1835, pp. 158, 159), says: “Among the known sources of this agent none seems so probable as the evaporation and condensation of watery vapor. We have the authority of two of the most able and accurate philosophers, Lavoisier and Laplace, for stating that bodies in passing from the solid or liquid state to that of vapor, and, conversely, in returning from the aeriform condition to the liquid or solid state, give unequivocal signs of either positive or negative electricity,” and he adds, in a footnote:

“M. Pouillet has lately published a set of experiments, which seems to overturn Volta’s theory of the evolution of electricity by evaporation. He has shown that no electricity is evolved by evaporation unless some chemical combination takes place at the same time ...” (Thomson, “Outlines,” p. 440) ... “But we shall be slow to reject the results of experiments performed by such experimenters as Lavoisier and Laplace, especially when confirmed by the testimony of Volta and Saussure.”

With regard to the origin of meteorites, Laplace has advanced the very bold theory that they may be products of Lunar volcanoes, and Prof. Lockhart Muirhead stated that he would “present the reasoning upon which this extraordinary hypothesis is founded in the popular and perspicuous language of Dr. Hutton, of Woolwich: the respect due to the name of Laplace justifying the length of the extract,” which he gives at pp. 633–635, Vol. XIV of the 1857 “Britannica.”

REFERENCES.--Humboldt, “Cosmos,” London, 1849, Vol. I. pp.
108–109; Young, “Course of Lectures,” London, 1807, Vol. II.
p. 501, alluding to “Zach. Mon. Corr.,” VI. p. 276, also
to Gilbert, XIII. p. 353, 108, and stating that Olbers had
suggested Laplace’s idea in 1795. See “Mem. of the Astronom.
Soc. of London,” Vol. III. p. 395: Laplace, “Mem. de l’Institut”
for 1809, p. 332; Dr. Young’s “Course of Lectures,” 1807, Vol.
I. pp. 249, 250, 522; Vol. II. p. 466; Humboldt, “Cosmos,”
London, 1849, Vol. I. pp. 28, 76, 130; Vol. II. p. 712;
Lavoisier at A.D. 1781: Biot at A.D. 1803; _Annal. de Ch. et
Phys._, Vol. XV. pp. 72, 73, and for Laplace and Lavoisier, see
Delaunay, “Manuel ...” 1809, p. 178; “Mem. de l’Acad. des Sc.,”
for 1781; “Journal des Savants,” for Feb. 1850 and Nov. 1887;
Houzeau et Lancaster, “Bibl. Gén.,” Vol. II. p. 184; “Cat. Sc.
Pap. Roy. Soc.,” Vol. III. pp. 845–848; Johnson’s “Cyclopædia,”
pp. 1647–1650 and the “First Supplement,” p. 62.

For Laplace and Joseph Louis Lagrange, see “Mémoires de
l’Institut,” Vol. III. p. 22; also “Pioneers of Science,” by
Sir Oliver Lodge, London, 1905, Lecture XI, and for Lagrange,
consult “Journal des Savants,” Sept. 1844, May 1869, August
1878, Sept. 1879, Sept. 1888 and Oct. 1892.

M. Cyrille Pierre Théodore Laplace, captain in the French navy, is the author of the “Voyage Autour du Monde ... sur la Corvette _Favorite_ ...” and of “Campagne de Circumnavigation de la Frégate _l’Artémise_ ...” published in Paris during the years 1833, 1839 and 1841.

Baron Jean Baptiste Fourier, celebrated French physicist (1768–1830) who, in 1827, succeeded Laplace as head of the Council of the Ecole Polytechnique (“Biog. Gén.,” Vol. XVIII. p. 346) says of his predecessor:

“Posterity, which has so many particulars to forget, will little care whether Laplace was for a short time minister of a great state. The eternal truths which he has discovered, the immutable laws of the stability of the world, are of importance, and not the rank which he occupied” (C. R. Weld, “Hist. Roy. Soc.,” Vol. II. p. 465). Fourier is the author of “Expériences thermo-électriques” (“Encycl. Brit.,” ninth ed., Vol. IX. p. 490; “Eng. Cycl.,” Biography, Vol. II. p. 977).

=A.D. 1820.=--Dutrochet (René Joachim Henri) (1776–1847) a distinguished French natural philosopher, and likewise medical adviser to the King of Spain, Joseph Bonaparte, publishes an interesting treatise on meteors, in conjunction with Mr. Nathaniel Bowditch, who had already written many very able papers on astronomical subjects and who afterwards translated the “Mécanique Céleste” of Laplace. Eight years later (1828) appeared Dutrochet’s “Nouvelles Recherches ...” wherein he attributes to electricity the direction taken by fluids through animal and vegetable membranes. The passage of a fluid from without inwardly he called _endosmosis_, and the passage of the fluid from within outwardly he termed _exosmosis_.

Of Dutrochet, Dr. John Hutton Balfour, of Edinburgh, makes mention when treating of the temperature of plants. He thus expresses himself: “While the nutritive processes are going on in the plant, there is a certain amount of heat produced. This, however, is speedily carried away by evaporation and other causes, and it is not easily rendered evident. Dutrochet, by means of Becquerel’s thermo-electric needle, showed an evolution of heat in plants. In doing this, he prevented evaporation by putting the plant in a moist atmosphere. In these circumstances the temperature of the active vegetating parts, the roots, the leaves, and the young shoots, indicated a temperature above the air of ½ to ¾ of a degree Fahrenheit. Van Beek and Bergsma, in their experiments on the _Hyacinthus Orientalis_ and the _Entelea Arborescens_, found the proper heat of the active parts of plants about 1·8° F. above that of the air. The vital or proper heat of plants, according to Dutrochet, is found chiefly in the green plants, and it undergoes a quotidian paroxysm, reaching the maximum during the day, and the minimum during the night. When stems become hard and ligneous, they lose this vital heat. Large green cotyledons gave indications of a proper heat. The hour of quotidian maximum varied from 10 a.m. to 3 p.m. in different plants.”

It is stated by Becquerel that in the act of vegetation, the earth acquires continually an excess of positive electricity, while the bark and part of the wood receive an excess of negative electricity. The leaves act like the green part of the parenchyma of the bark--that is to say, the sap which circulates in their tissues is negative with relation to the wood, to the pith, and to the earth, and positive with regard to the cambium. The electric effects observed in vegetables are due to chemico-vital action, and he asserts that the opposite electric states of vegetables and of the earth give reason to think that, from the enormous vegetation in certain parts of the globe, they must exert some influence on the electric phenomena of the atmosphere.

REFERENCES.--Gmelin’s “Chemistry,” Vol. I. p. 447; “Biog.
Gén.,” Vol. XV. p. 506; Poggendorff, “Annalen,” Vol. I. p. 663;
Larousse, “Dict. Univ.,” Vol. VI. p. 1448; J. W. Ritter, in
“Denkschr. d. Münch. Acad.” for 1814, and the eighth ed. of the
“Ency. Brit.” Vol. XXI. p. 635, for observations concerning the
_mimosa pudica_ and the _mimosa sensitiva_; “Cat. Sc. Papers
Roy. Soc.,” Vol. II. pp. 422–425; Vol. VI. p. 646; Vol. VII. p.
584; Poggendorff, Vol. I. p. 633; “Observations on the diurnal
variation of the magnetic needle,” in Sturgeon’s “Annals,” Vol.
VII. pp. 369–370, and in the _Comptes Rendus_, Vol. XII. p.
298, of Feb. 8, 1841; Burnet, “On the motion of sap in plants.
Researches of Dutrochet on Endosmose and Exosmose ...” London,
1829 (“Phil. Mag. or Annals,” Vol. V. p. 389).

=A.D. 1820.=--Fresnel (Augustin Jean) (1788–1827), one of the most distinguished French mathematicians and natural philosophers, communicates a paper detailing his experiments for decomposing water by means of a magnet. He produced a current in an electro-magnetic helix enclosing a bar-magnet covered with silk, and on plunging the ends of the wire in water he observed some very remarkable effects which are set forth in the _Annales de Chimie et de Phys._, series 2, Vol. XV. p. 219.

REFERENCES.--“Eloge de Fresnel,” by Arago, in his “Œuvres,” Vol.
I; Account of Fresnel’s life in the “Biog. Univ.;” Whewell,
“Hist. of Induc. Sci.,” 1859, Vol. II. pp. 96, 102, 114–117;
“Œuvres complètes d’Augustin Fresnel, publiées par les soins du
Ministre de l’Instruction Publique,” Paris, 1870, in three vols.

=A.D. 1820.=--Sir Richard Phillips (1778–1851), communicates, July 11, to the _Philosophical Magazine_ (Vol. LVI. pp. 195–200) a very interesting paper entitled “Electricity and Galvanism Explained on the Mechanical Theory of Matter and Motion.” After reviewing the then existing theories, he concludes by saying:

“Electricity is no exception to the mechanical principles of matter and motion, and in regard to the kindred phenomena of galvanism, I will content myself with observing that it is merely _accelerated electricity_, the interposing fluid being palpably decomposed and evolving the electrical powers, each term in the series of plates being a new impulse or power added to the previous one, till the ultimate effect is accelerated, like that of a body falling by the continuous impulses of the earth’s motions, or like a nail heated red-hot by accelerations of atomic motion produced by repeated percussions of a hammer.”

Consult “Bibl. Ital.,” Vol. XXVII. p. 107 for references to the “Annals of Philosophy,” in which he mentions an experiment upon a young poplar, “whereby it would seem that copper was imbibed in the branches, etc., from a solution placed at its roots, and that it was precipitated on a knife used to cut off a branch.”

=A.D. 1820.=--Brewster (Sir David) (1781–1868), a very distinguished English natural philosopher and writer, who had just founded the “Edinburgh Philosophical Journal” in conjunction with Prof. Robert Jameson, announces his discovery of the existence of two poles of greatest cold on opposite sides of the northern pole of the earth. By this he was, like other authors, led to the belief that there might be some connection between the magnetic poles and those of maximum cold, and he remarks (Noad “Manual,” London, 1859, p. 545, and article “Magnetism” in “Encycl. Brit.”): “Imperfect as the analogy is between the isothermal and magnetic centres, it is yet too important to be passed over without notice. Their local coincidence is sufficiently remarkable, and it would be to overstep the limits of philosophical caution to maintain that they have no other connection but that of accidental locality; and if we had as many measures of the mean temperature as we have of the variation of the needle, we might determine whether the isothermal poles were fixed or movable.” Similar opinions entertained by Dr. Dalton, Dr. Traill and Mr. Christie are also mentioned by Noad, who quotes from Oersted’s treatise on “Thermo-Electricity” the statement of the Danish philosopher “that the most efficacious excitation of electricity upon the earth appears to be produced by the sun, causing daily evaporation, deoxidation and heat, all of which excite electrical currents.”

From his able paper in the _Edinburgh Philosophical Transactions_ for 1820, one is led to share Sir David Brewster’s belief “that two meridians of greatest heat and two of greatest cold are called into play, and that the magnetism of our globe depends in great measure upon electro or rather thermo-magnetic currents.” The electro-magnetic hypothesis was, he says, ably supported by Prof. Barlow in his paper “On the probable electric origin of all the phenomena of terrestrial magnetism,” communicated to the _Phil. Trans._ for 1831. Brewster thus locates the two poles of maximum cold: The American pole in N. Lat. 73, and W. Long. 100 from Greenwich, a little to the East of Cape Walker; the Asiatic pole in N. Lat. 73 and E. Long. 80, between Siberia and Cape Matzol, on the Gulf of Oby. Hence the two warm meridians will be in W. Long. 10 and E. Long. 170, and the two cold meridians in W. Long. 100 and E. Long. 80.

As has already been indicated (under A.D. 1717, Leméry), Sir David Brewster was the discoverer of the pyro-electrical condition of the diamond, the garnet, the amethyst, etc. His development of some of Haüy’s experiments led to a similar discovery, attaching to several mineral salts as well as to the plates and powders of the tourmaline, of the scolezite and the melozite; and he likewise experimented with the boracite, mesotype and with the several minerals and artificial crystals detailed at pp. 208–215, Vol. I of the _Edin. Jour. of Science_, London, 1826; and in Chap. II. s. 1, vol. viii of the eighth “Encycl. Brit.,” article on “Electricity.”

At Part I. chap. i. s. 6 of the last-named article will be found Brewster’s observations on the nature and origin of electrical light, his latest researches having been made, like those of Joseph von Fraunhofer (see A.D. 1814–1815), on the dark and on the luminous lines which appear in the spectrum formed from it by a prism.

During the year 1831 appeared Brewster’s “Treatise on Optics,” his “Life of Sir Isaac Newton,” and his “Letters on Natural Magic.” It is in one of the chapters of the last-named work that he treats of automatic talking machines and remarks: “We have no doubt that before another century is completed a talking and a singing machine will be numbered among the conquests of science.”

Brewster’s other scientific treatises are too numerous and cover too wide a range to be enumerated here. The “Catal. of Sci. Papers of the Roy. Soc.” (Vol. I. pp. 612–623) gives the titles of as many as 299 contributions made by him on important subjects, and he has had no less than 76 papers in the first 39 parts of the _North British Review_, 30 in the _Phil. Trans._ and 28 in the _Edin. Review_. They appear, in fact, in all the prominent publications of his time, and have won for him leading honours, more especially from the Edinburgh and Aberdeen Universities and the Scotch, Irish, English and French Societies, the French Academy of Sciences doing him the signal honour of selecting him as one of its eight foreign associates in place of Berzelius, deceased. Conjointly with Davy, Herschel and Charles Babbage, he originated the British Association during 1831, and it was in this same year that he was knighted and decorated by King William IV. He had been made a Fellow of the Royal Society of Edinburgh in 1808, and had during the same year undertaken the editorship of the “Edinburgh Encyclopædia of Sci., Lit. and Art.” This he continued for twenty-two years, after which he edited the _Edin. Jour. of Sci._, and also entered with Taylor and Phillips upon the editorship of the _London and Edin. Phil. Mag. and Journal_. Many of our readers will doubtless be glad to know that the last named was a continuation of the well-known _Philosophical Magazine_ so often quoted in this “Bibliographical History.”

REFERENCES.--The obituary notice contributed by Dr. J. H.
Gladstone to the proceedings of the Royal Society; _Chemical
News_, Amer. reprint, Vol. II. pp. 198, 233; also p. 293 for
accounts given by Sir J. Simpson and Prof. Fraser; J. Robison
and Brewster, “A System of Mechan. Phil.,” London and Edin.,
1822; Ferguson and Brewster’s “Essays and Treatises on Astr.
Elect.,” etc., Edinburgh, 1823; Brewster’s several articles in
the “Encycl. Britannica,” 7th and 8th editions, on “Electricity
and Magnetism”; _Transactions of the Roy. Soc. of Edinburgh_,
Vols. IX. 1821; XX. Part IV; _Edin. Jour. of Sci._, Oct.
1824, No. 2, p. 213; Noad, “Manual,” London, 1859, pp. 31,
32, 636–638; Harris, “Magnetism,” Part III. p. 119; Whewell,
“Hist. of Induc. Sci.,” 1859, Vol. II. pp. 75, 81, 331, 332; the
lectures delivered by Wm. A. Miller during 1867 before the Royal
Institution of Great Britain.

Charles Babbage (1792–1871), a prominent English scientist who is mentioned above and who besides being one of the founders of the Royal Astronomical Society, as has already been stated, was also a founder of the British Association and the originator of the Statistical Society, is the author of valuable papers, exhibiting a wide range of learning and research--mainly on mathematical subjects and relating to magnetical and electrical phenomena--which have been published in the Reports of the Royal and other Societies (“English Cycl.,” Vol. I. p. 457; “Encyl. Brit.,” ninth ed., Vol. III. p. 178; Larousse, “Dict.,” Vol. II. pp. 5–6; account of Babbage’s work in C. R. Weld’s “Hist. Roy. Soc.,” Vol. II. pp. 369–391).

=A.D. 1820.=--Fisher (George) (1794–1873), who two years before had joined Captain David Buchan in his voyage to the Arctic regions, is the first to point out the true cause of the sudden alteration in the rates of chronometers at sea. “He observed,” says Dr. Roget, “that the chronometers on board the ‘Dorothea’ and ‘Trent’ had a different rate of going from that they had on shore, even when these vessels had been frozen in, and therefore when their motion could not have contributed to that variation; ... this effect could be attributed only to the magnetic action exerted by the iron in the ships upon the inner rim of the balance of the chronometers, which is made of steel. A similar influence was perceptible on placing magnets in the neighbourhood of the chronometers. This conclusion was confirmed by experiments made for this purpose by Mr. Barlow, who ascertained that masses of iron devoid of all permanent magnetism occasioned an alteration in the rates of chronometers placed in different positions in their vicinity.”

REFERENCES.--Fisher’s article “On the Errors in Longitude as
Determined by Chronometers at Sea, Arising from the Action of
the Iron in the Ships upon the Chronometers,” communicated
by John Barrow, F.R.S., to the _Phil. Mag._, Vol. LVII. pp.
249–257. See besides, _Edinburgh Jour. Sci._, London, 1826, Vol.
V. p. 224; _Phil. Trans._ for 1820, Part. II. p. 196, and the
volume for 1833, relative to magnetical experiments; also the
“Lib. U. K.” (Magn.), p. 63. For Capt. Buchan, consult Barrow’s
“Chronological History of Voyages into the Arctic Regions.”

Mr. George Thomas Fischer (1722–1848) is the author of “A Practical Treatise on Medical Electricity” (Poggendorff, Vol. I. p. 756).

=A.D. 1820.=--Bonnycastle (Charles), Professor of Mathematics in the University of Virginia, treats of the distribution of the magnetic fluids in masses of iron, as well as of the deviations which they produce in compasses placed within their influence, at pp. 446–456, Vol. LV of Tilloch’s _Philosophical Magazine_.

He refers to the then recent publication of Peter Barlow’s “Essay on Magnetic Attractions,” containing the results of many experiments, made principally upon spheres of iron, as well as to Dr. Young’s views of the subject, which were printed by order of the Board of Longitude, and he says that the principle upon which he intends establishing his inquiry “is an extension of the law that regulates the action of electrified bodies upon conductors; which was first given by M. Poisson in the Memoirs of the Institute for 1811, and employed by him to determine the development of the electric fluids in spheres that mutually act on each other.”

The afore-named dissertation, at the time, called forth a rejoinder from a correspondent and a further communication from Mr. Bonnycastle, both of which appear at pp. 346–350, Vol. LVI of the same publication.

REFERENCES.--Silliman’s _Journal_, Vol. XL. p. 32; “Sketch of
the Life of Chas. Bonnycastle,” by Thomas Thomson; Poggendorff,
Vol. I. pp. 234, 235; article “Magnetism,” p. 9, Vol. XIV of the
eighth “Britannica.”

=A.D. 1820.=--Harris (Wm. Snow), member of the College of Surgeons, and a very distinguished English scientist (1791–1867), proposes to the Board of the Admiralty his system of lightning conductors, of which an account appears at p. 231, Vol. LX of the _Phil. Mag._, as well as in a separate work published at London during 1822. This is followed by his “Observations on the Effects of Lightning ...” 1823, and by papers relative to the defence of ships and buildings from lightning, which were published, more particularly, in several numbers of the _Nautical Magazine_, the _Phil. Mag._, the _Annals of Electricity_, and in the _Proc. Lond. Elec. Soc._ for 1842, as well as in his “Record of Phil. Papers,” and under separate heads during many years between 1827 and 1854. One of his biographers remarks:

“His researches have gone far to remove certain popular errors as to what have been called ‘conductors’ and ‘non-conductors’ of electricity, and to show the inutility of the old form of lightning rod in the majority of cases; it being necessary, in place of such rod form, to link into one great chain all the metallic bodies employed in the construction of a building, thus providing a connection with these conductors between the highest parts and the ground, the single conductor, in one highest part, being possibly insufficient to divert the course of the fluid and protect the whole fabric. These general principles have been largely applied to the protection of the ships of the Royal Navy during the last five and twenty years, under his advice and direction; and, laying aside the opinions which had been commonly received, the masts themselves of a ship have all been rendered perfectly conducting by incorporating with the spars capacious plates of copper, whilst all the large metallic masses in the hull have been tied, as it were, into a general conducting chain, communicating with the great conducting channels in the masts, and with the sea. This may be considered as the greatest experiment ever made by any country in the employment of metallic conductors for ships, and the result has been to secure the navy from a destructive agent, and to throw new light upon an interesting department of science” (Whewell, “Hist. of Induc. Sci.,” Vol. II. pp. 199, 200; _Phil. Mag._ for March 1841; eighth “Encycl. Britannica,” Vols. VIII. pp. 535, 610, 611, and XX. p. 24; “Edin. Review” for Oct. 1844, Vol. LXXX. pp. 444–473).

Harris was the first, says Brewster, who introduced accurate quantitative measures into the investigation of the laws of statical electricity--the unit measure by which quantity is minutely estimated--and also the hydro-electrometer and scale-beam balance by which its intensity and the laws of attractive forces at all distances are demonstrated. Of not less value is the thermo-electrometer, by which the heating effects of given quantities of electricity are measured and rendered comparable with the varying conditions of quantity and intensity. Besides these instruments, we owe to Harris the discovery of a new reactive force, through which repulsion and other small physical forces are investigated and determined by means of his bifilar balance, founded upon the reactive force of two vertically suspended parallel threads when twined upon each other at a given angle, and acted upon by a suspended weight. With the aid of these instruments he has carried on a variety of important inquiries into the laws of electrical forces, and the laws and operations of electrical accumulation (eighth “Brit.,” Vol. VIII. p. 535). His papers on the subject appeared in 1825 and 1828, and a _résumé_ of them is given by Noad (“Manual” 1859, pp. 35, 137–140), as well as in the “Electricity” article of the “Britannica,” both of which contain descriptions and illustrations of Harris’ unit jar and electro-thermometer.

During the year 1827 Mr. Harris published in the _Trans. Roy. Soc. of Edinburgh_ his memoir entitled “Experimental Inquiries Concerning the Laws of Magnetic Forces,” which experiments were made by means of a new and very accurate apparatus invented by him for examining the phenomena of induced magnetism. The above was followed by two other memoirs, published in the _Phil. Trans._ for 1831, “On the Influence of Screens in Arresting the Progress of Magnetic Action ...” and “On the Power of Masses of Iron to Control the Attractive Force of a Magnet,” which are discoursed of in the “Britannica” article on “Magnetism,” wherein special treatment is also given more particularly to Mr. Harris’ researches concerning artificial magnets as well as the magnetic charge, the development of magnetism by rotation and the phenomena of periodical variations (“Rudim. Mag.,” Part III. p. 60; Fahie’s “Hist, of Elec. Tel.,” pp. 283, 284).

Besides additional apparatus named in the subjoined references Mr. Harris invented a very effective steering compass, of which an account is given in Part III. pp. 148–153, of his “Rudimentary Magnetism,” as well as at p. 594 of Noad’s “Manual,” at p. 105 of the “English Cyclopædia” (Arts and Sciences), Vol. III, and at p. 80, Vol. VIII, 1857, “Encycl. Britannica,” and he has also devised a magnetometer for the measurement of electric forces, of which the description and illustrations appear in the last-named publication as transcribed from Mr. Harris’ work already mentioned.

Mr. Harris was made a F. R. S. in 1831, and received the Copley medal four years later. It was in 1843 he published his well-known work “On the Nature of Thunderstorms,” the plans he advocated being adopted in 1847, when he received the order of knighthood as well as a large money grant from the English Government in acknowledgment of his scientific services. The following appears in the obituary notice of Sir Wm. Snow Harris, contributed by Mr. Charles Tomlinson to the _Proceedings of the Roy. Soc._ (XVI, 1868):

“Harris’ sympathies were with the Bennetts, the Cavendishes, the Singers, the Voltas of a past age. Frictional electricity was his _forte_ and the source of his triumphs. He was bewildered and dazzled by the electrical development of the present day, and almost shut his eyes to it. He was attached too closely and exclusively to the old school of science to recognize the broad and sweeping advance of the new. He was not conscious even of being behind his age when he presented to the Royal Society in 1861 an elaborate paper on an improved form of Bennett’s discharger, and still less in 1864, when he discussed the laws of electrical distribution, and yet relied upon the Leyden jar and the unit jar.”

REFERENCES.--_Trans. of the Plymouth Institution_, also _Trans.
of the Roy. Soc._ for 1834, 1836, 1839; “Eng. Encycl.” (“Common
Electricity”), Vol. III. p. 801; W. A. Miller, “Elem. of Chem.,”
1864, p. 32. For descriptions of his bifilar balance see the
eighth “Britannica,” Vol. VIII. p. 623; Harris, “Rud. Elec.,”
p. 99, and “Rud. Magn.,” pp. 119, 120; Noad, “Manual,” pp. 26,
27, 37, 40, 41, 63, 580; C. Stahelin, “Die Lehre ...” 1852;
P. Volpicelli, “Ricerche analitiche ...” Roma, 1865, while,
for his balance electroscope and electrometers, see “Edin.
Phil. Trans.,” Dec. 1831; eighth “Britannica,” Vol. VIII. pp.
540, 590, 620 622, 624; Harris, “Rud. Elec.,” pp. 99, etc.;
the “Bakerian Lecture”; the “Report of British Association,”
Dundee, 1867, for an able account of electrometers by Sir
William Thomson. His electrical machine is described at pp.
74–76 of Noad’s “Manual,” as well as at p. 604, Vol. VIII
of the 8th “Britannica,” the latter also giving, at p. 550,
Harris’ experiments on the electrical attraction of spheres and
planes. “Catal. Sc. Papers Roy. Soc.,” Vol. III. pp. 191–192;
Lippincott’s “Biog. Dict.,” 1886, p. 1230; Biography in Harris’
“Frictional Electricity”; “Abstracts of Papers ... Phil. Trans.,
1800–1830,” Vol. II. p. 298; _Lumière Electrique_ for Oct. 3,
1891, p. 49; reprint of Sir Wm. Thomson’s “Mathematical Papers,”
1872; “Brit. Asso. Reports” for 1832, 1835, 1836; _Edin. Phil.
Trans._ for 1834; Fahie’s “History,” p. 321; _Edin. and London
and Edin. Phil. Mag._ for 1840; _Phil. Trans._, 1842; _Phil.
Mag._ for 1856–1857, and Harris’ “Manuals of Electricity,
Galvanism and Magnetism,” published in John Weale’s Rudimentary
Series.

=A.D. 1820.=--Mitscherlich (Eilardt--Eilhert), Professor of Chemistry at the Berlin University, discovers what is called _Isomorphism_ (_isos_, equal; _morphe_, form), showing that bodies containing very different electro-positive elements could not well be distinguished from each other; it was impossible therefore to put them in distant portions of the classification, and thus, remarks Whewell, the first system of Berzelius crumbled to pieces.

In other words, Mitscherlich was the first to draw attention to the fact that two bodies having the same composition could assume different forms; to this law Berzelius gave the name of _Isomerism_ (_isos_, equal; _meros_, part).

Sir John Herschel makes particular mention (“Treatise on Light,” s. 1, 113) of Mitscherlich’s remarkable experiment with sulphate of lime--the alteration in the tints of which by heat, it is said, was first observed by Fresnel. This experiment was repeated by Sir David Brewster, and he discovered still more curious properties in _glauberite_, all of which are detailed in Vol. I. p. 417 of the _London and Edinburgh Phil. Mag._ for Dec. 1832.

REFERENCES.--“Cat. Sci. Papers Roy. Soc.,” Vol. IV. pp. 413–416;
“Library Useful Knowledge” (Pol. of Light), p. 63; Poggendorff,
Vol. II. pp. 160, 161; the very able treatise of Mr. J. Beete
Jukes on “Mineralogical Science”; also Poggendorff’s _Annalen_,
Vol. XV. p. 630, for Mitscherlich on the chemical origin of iron
glance in volcanic masses.

=A.D. 1820.=--Ampère (André Marie) (1775–1836), one of the most distinguished philosophers of the century, Professor of Mathematical Analysis in the French Ecole Polytechnique (1809), afterwards Professor of Physics at the Collège de France, reads before the Académie Royale des Sciences, Sept. 18, 25, Oct. 9, 13, and Nov. 6, 1820, papers containing a complete exposition of the phenomena of electro-dynamics. His investigations were subsequently embodied in the “Recueil d’Observations ...” Paris, 1822, and were still further developed during 1824 and 1826, as shown through both his “Précis de la théorie ...” and “Théorie des Phénomènes Electro-Dynamiques.”

The news of Oersted’s discovery of the relation existing between the electric current and the magnet--the fundamental fact of electro-magnetism--was made known in July 1820, and the inquiry was at once taken up more particularly by Ampère, Arago, Biot, and Félix Savary in France, as well as by Berzelius, Davy, De la Rive, Cumming, Faraday, Joseph Henry, Schweigger, Seebeck, Sturgeon, Nobili and others throughout Europe and elsewhere. Of all these scientists, Ampère proved the most energetic, and, within three months of the announcement of Oersted’s discovery, his first memoir on the subject was publicly read in Paris.

In this first paper, Sept. 18, he explains the law determining the position of the magnetic needle in relation to the electric current, and he also makes known his intended experiments with spiral or helical wires, which he predicts will acquire and retain the properties of magnets so long as the electrical current flows through them. He likewise explains his theory of magnets, saying that if we assume a magnet to consist of an assemblage of minute currents of electricity whirling all with the same direction of rotation around the steel molecules and in planes at right angles to the axis of the bar, we will have an hypothesis which will account for all the known properties of a magnet. He constructed his spirals and helices, and to the astonishment of all, he produced magnets formed only of spools of copper wire traversed by electric currents. We can readily imagine, adds Prof. A. M. Mayer, the intense interest awakened by this discovery, a discovery which caused Arago to exclaim, “What would Newton, Halley, Dufay, Æpinus, Franklin and Coulomb have said if one had told them that the day would come when a navigator would be able to lay the course of his vessel without a magnetic needle and solely by means of electric currents?” “The vast field of physical science,” says Arago, “perhaps never presented so brilliant a discovery, conceived, verified and completed with such rapidity.” Thus Ampère became the author of a beautiful generalization, which not only included the phenomena exhibited by the new combinations of Oersted, but also disclosed forces existing in arrangements already familiar, although they were never detected till it was thus pointed out how they were to be looked for. His electro-dynamic theory of the action of currents and of magnets has been thought worthy of a place near the Principia of Newton ... it deservedly gained for him the title of the Newton of electro-dynamics, as he did for this branch of science even more than Coulomb had previously done for electro-statics (Profs. A. M. Mayer and W. B. Rogers, “Memorial of Jos. Henry,” 1880, pp. 81, 476; Lardner, “Lectures,” 1859, Vol. II. p. 120; Fahie, “Hist. Tel.,” p. 276).

The experiments of Oersted and Ampère were at once greatly extended by many scientists, among whom may be especially mentioned MM. Yelin, Bœckmann, Van Beek, De la Rive, Moll, Nobili, Barlow and Cumming. The last named apparently gave the earliest notice of the increased effects of a convolution of wire around the magnetic needle, and constructed the first astatic needle galvanometer (_Trans. Camb. Soc._, Vol. I. p. 279). The Chevalier Julius Konrad Yelin (1771–1826), German mathematician, ascertained that the electricity of an ordinary machine when passed along a helix, either in simple electrical sparks or by discharges from a battery, has the effect of rendering an included needle magnetic. According to Dr. Henry, M. Bœckmann found in varying these experiments that no modification of the effect is produced by altering the diameter of the helix from half an inch to thirteen inches. With a helix of thirty-four inches diameter, and a coated surface of 300 square inches, much less magnetism was, however, imparted; and with one of eighty-four inches it was scarcely perceptible. It was found that a needle outside of the helix was magnetized as much as one within; that after being once fully magnetized a continuation of the discharges diminished its power; and that five jars, each of 300 square inches, did not produce, by repeated discharges, much more effect than one of them (Poggendorff, Vol. II. p. 1382; Gilbert’s _Annalen_ for 1820–1823).

In his second paper, Sept. 25 (_Ann. de Chim. et de Phys._, Vol. XV. pp. 59–170), Ampère makes known the results of his experiments on the mutual attractions and repulsions of electrical currents, showing conclusively that when the voltaic current is passed in the same direction through two parallel wires, so placed as to move freely, they attract each other, and that they are repelled if the currents are passed in opposite directions. Thus he establishes the second fundamental law of electro-magnetism, the first law, instituted as we have seen by Oersted, being that the magnetical effect of the electrical current is a circular motion around the current. In the last-named paper he also proposes the hypothesis of currents of electricity circulating from east to west around the terrestrial globe in planes at right angles to the direction of the dipping needle, to account for the phenomena of terrestrial magnetism (Roget, “Electro-Magn.,” p. 47).

In his third paper, Oct. 9, Ampère investigates the properties of currents transmitted through wires forming closed curves (_courbes fermées_) or complete geometrical figures, an inquiry also alluded to in another memoir read Oct. 30, 1820.

These papers were immediately followed by others, which engaged nearly all the sittings of the Academy between Dec. 4, 1820, and Jan. 15, 1821. In these he brings forth new confirmations of his theories, and reduces the phenomena of electro-magnetism to mathematical analysis.

Mr. Samuel Prime remarks (“Life of Morse,” 1875, p. 266) that the discovery of the action of the spiral coil upon the magnetic needle seems to have been independently made by Ampère in 1821:

“I showed that the current which is in the pile acts on the magnetic needle by the conjunctive wire. I described the instrument, which I proposed to construct, and, among others, the galvanic spiral. I read a note upon the electro-chemical effects of a spiral of iron wire, subjected to the action of the earth, directing an electric current as well as a magnet. I announced the new fact of the attraction and repulsion of two electric currents, without the intermediation of any magnet, a fact which I had observed in conductors twisted spirally (Tilloch’s _Journal of Science_, Vol. LVII. p. 47, 1821).

One of his biographers, Professor Chrystal says: “Scarcely had the news of Oersted’s discovery reached France, when a French philosopher, Ampère, set to work to develop the important consequences which it involved. Physicists had long been looking for the connection between magnetism and electricity, and had, perhaps, inclined to the view that electricity was somehow to be explained as a magnetic phenomenon. It was, in fact, under the influence of such ideas, that Oersted was led to his discovery. Ampère showed that the explanation was to be found in an opposite direction. He discovered the ponderomotive action of one electric current on another, and, by a series of well-chosen experiments, he established the elementary laws of electro-dynamic action, starting from which, by a brilliant train of mathematical analysis, he not only evolved the complete explanation of all the electro-magnetic phenomena observed before him, but predicted many hitherto unknown. The results of his researches may be summarized in the statement that an electric current, in a linear circuit of any form, is equivalent in its action, whether on magnets or other circuits, to a magnetic shell bounded by the circuit, whose strength at every point is constant and proportional to the strength of the current. By his beautiful theory of molecular currents, he gave a theoretical explanation of that connection between electricity and magnetism which had been the dream of previous investigators. _If we except the discovery of the laws of the induction of electric currents_, made about ten years later by Faraday, _no advance in the science of electricity can compare for completeness and brilliancy with the work of Ampère_. Our admiration is equally great, whether we contemplate the clearness and power of his mathematical investigations, the aptness and skill of his experiments, or the wonderful rapidity with which he elucidated his discovery when he had once found the clew.”

“Oersted,” remarks M. Babinet, “was the Christopher Columbus of magnetism; Ampère became its Pizarro and its Fernand Cortez.”

Of Ampère’s _astatic_ needles, a description, taken from one of his memoirs (_Ann. de Ch. et de Ph._, Vol. XVIII. p. 320), appears at pp. 280–281 of Fahie’s “History” (Knight’s “Mech. Dict.,” 1874, Vol. I. p. 171, and Vol. II. p. 1181). For this greatly perfected form of galvanometer the credit has erroneously been given to Prof. Cumming, who first suggested the idea of neutralizing the directive force of the needle arising from the earth’s magnetism, which he did by placing a magnetized needle immediately beneath the movable or index needle. Fahie adds, in a footnote: “In Prof. Cumming’s paper ‘On the Connection of Galvanism and Magnetism,’ read before the Cambridge Philosophical Society, April 2, 1821, he described a near approach to the astatic needle. In order to neutralize the terrestrial magnetism he placed a small magnetized needle under the galvanometer needle” (_Trans. Cam. Phil. Soc._, Vol. I. p. 279). The credit of Ampère’s discovery is sometimes given to Nobili, as in Noad’s “Manual of Electricity,” London, 1859, p. 327; also Roget’s “Electro-Magnetism” in “Library of Useful Knowledge,” London, 1832, p. 42.

As has been already shown (Laplace, A.D. 1820), the first proposal to apply Oersted’s discovery to telegraphic purposes by substituting the deflection of the magnetic needle through electric currents for the divergence of the pith balls of the electroscope, was made by Ampère, in his Memoir of Oct. 2, 1820, which appears in the _Comptes Rendus_, and at p. 72, Vol. XV of the _Annales de Chimie et de Physique_. His plan, remarks Sabine, was, however, doomed to the same fate as that of Sömmering, of never coming into practice, and for the same reasons, principally the number of line wires. Had Ampère combined his system, or rather the one of Laplace, with that which Schweigger proposed of reducing Sömmering’s telegraph to two wires, or with any other using a code of signals, the problem of the electric telegraph would have been solved from the year 1820. Ampère makes no mention of surrounding the needles with _coils of wire_, as is so frequently stated by writers on the telegraph. Indeed he could not then have even heard of the galvanometer; for, although Schweigger’s paper on the subject was read at Halle on the 16th of September 1820, it was not published until the November following.

M. Jean Jacques Antoine Ampère (1800–1864), son of André Marie Ampère, was an accomplished scholar who succeeded François Andrieux as professor at the Collège de France and became a member of the French Academy in 1847.

REFERENCES.--For accounts of Ampère’s rotary magnet,
electro-dynamic cylinders, revolving battery, and of his
electripeter employed to alter rapidly the direction of the
electric current in voltaic batteries, consult pp. 639, 640,
643, Vol. VIII of the eighth “Britannica.” Fahie, “Hist. of
El. Tel.,” p. 303. See “Catal. Sci. Papers Roy. Soc.,” Vol.
I. pp. 58, 61; Messrs. Sainte-Beuve et Littré’s account of
his life and labours in the _Revue des Deux Mondes_ for Feb.
15, 1837; “Notice sur M. Ampère,” _par_ M. E. Littré, Paris,
1843; Arago’s “Eulogy on Ampère,” translated, at pp. 111–171 of
the “Report of the Smithsonian Institution” for 1872. Consult
also “Report Smiths. Instit.” for 1857, pp. 100–107; Ampère’s
biography in the _Sci. Am. Suppl._, No. 674, p. 10760; also
Ampère’s “Journal et Correspondance,” Poggendorff, Vol. I. pp.
39, 40; Address of His Royal Highness the Duke of Sussex to
the Eng. Roy. Soc., 1836; Barlow on “Magnetic Attractions”:
_Comptes Rendus_ for 1838, Vol. VII. p. 81; _Bibl. Univ._,
XX; _Phil. Mag._, Vols. LVI. p. 308; LVII. pp. 40–47, “On the
Electro-Magnetic Experiments of Oersted and Ampère,” by Mr.
Hatchett, and pp. 47–49; _Ann. de Phys. de Bruxelles_, Vol.
VII; _Ann. de Ch. et de Phys._, XXIX; Du Moncel, Vol. III. p.
7; “Acad. de Paris,” Sept. 12, 1825; _La Lum. Elect._ for Oct.
31, 1891, p. 202; Roch, in “Zeitschr. f. Mathém.” 1859, p. 295;
Roget on Ampère’s theory of Mag.; K. W. Knochenhauer, _Pogg.
Annal._, XXXIV. p. 481; J. Marsh, “On a Particular Construction
of M. Ampère’s Rotating Cylinder,” _Phil. Mag._, LIX. p. 433,
1822; Henn, “De Amperi principiis ...”; “Memorial of Joseph
Henry,” 1880, pp. 59, 81; “Lib. of Use. Know.” (El. Mag.), pp.
24, 28, 83–92; Harris, “Rud. Elec.,” pp. 170, 171, and “Rud.
Mag.,” p. 130; Noad, “Manual,” pp. 661–662, 861–864; “Encycl.
Metrop.” (El. Mag.), Vol. IV. pp. 5–8; Highton, “Elec. Teleg.,”
p. 39; Gmelin’s “Chemistry,” Vol. I. p. 317; Mrs. Somerville,
“Conn. Phys. Sci.,” 1846, pp. 320, 321; Dr. Lardner, “Lectures,”
Vol. II. p. 125; J. F. W. Herschel, “Prelim. Dis. Nat. Phil.,”
1855, p. 243; Whewell, “Hist. Induc. Sc.,” 1859, Vol. II. pp.
242, 246, 619; “Ann. of Sc. Disc.” for 1850, p. 129, and for
1865, p. 125; “Smithsonian Report” for 1878, p. 273; Sturgeon,
“Sci. Researches,” Bury, 1850, pp. 12, 16, 29; _Jour. Frankl.
Inst._ for 1851, Vol. XXII. p. 59; Turnbull, “El. Mag. Tel.,”
1853, pp. 55 and 221; (Vail’s “History,” pp. 133, 134; Prof.
Henry’s Evid., 85a, record; Doct. Channing’s Ev., 47a, record;
Hibbard, Ev., 31_a_. ...) See also Humboldt’s “Cosmos,”
articles “Aurora Borealis,” “Volcanoes,” “Earthquakes”; Ampère
et Babinet, “Exposé des Nouv. Déc. ... de Oersted, Arago,
Ampère, Davy, Biot, Erman, Schweigger, De la Rive,” etc.,
Paris, 1822, translated into German “Darstellung der neuen ...
dem Französischen,” Leipzig, 1822, and alluded to in _Lumière
Electrique_ for July 18, 1891, pp. 148, 149; Hachette et
Ampère, “Sur les Expériences de Oersted et Ampère”: _Journal
de Physique_ for September 1820. _Annales de Chimie_ for 1825;
“Journal des Savants,” for June 1872; “Dict. Génér. de Biogr. et
d’Histoire,” Paris, 2^e ed., pp. 85–86; “Collection de Mémoires
relatifs à la Physique,” Paris 1885, 1887, Vols. II and III
_passim_, as per indexes; “Amer. Journ. of Psychology,” Vol. IV.
pp. 6–7.

For William Ritchie (1790–1837), the author of an able paper, “On electro-magnetism, and Ampère’s proposal of telegraphic communication by means of this power,” consult _Phil. Trans._ for 1833, p. 313; “Abstracts of Papers ... Roy. Soc.,” Vol. II. pp. 350, 382; _Phil. Mag._ or _Annals_, Vol. VII, 1830, p. 212; _Phil. Mag. and Journal of Science_, Vol. III, 1833, pp. 37, 122, 124, 145.

For Leopoldo Nobili (1784–1835), frequently mentioned above, consult “Bibl. Univ.,” Bruxelles, 1834 (Sc. et Arts), Tome LVI. pp. 82–89, 150–168; “Edin. Trans.” Vol. XII and _Phil. Mag._ Vol. XI, 1832, p. 359, for the account of experiments made by James David Forbes, similar to those of Nobili, wherein an electric spark was elicited from a natural magnet. For J. D. Forbes, see also _Phil. Mag._, 1832, Vol. XI. p. 359. For Nobili and Antinori, consult _Phil. Mag._, Vol. XI, 1832, pp. 401, 466; “Bibl. Britan.,” Vol. XXV, 1824, N.S. p. 38; Vol. XXIX, 1825, N.S. p. 119. For Antinori and Marchese Cosimo Ridolfi, consult “Bibl. Britan.” Vol. XVI, N.S., 1821, pp. 72–75, 101–118.

For Prof. James Cumming (1777–1861), also frequently named in above article, consult _Phil. Mag._, Vol. LX, 1822, p. 253; “Bibl. Britan.,” Vol. XXV, N.S., 1824, p. 104, for experiments of Cumming, Trail and Marsh; the investigations in the same line of Mr. Thos. Stuart being especially reported on in “Bibl. Britan.,” Vol. XXVII, N.S., 1824, pp. 199–206; “Dict. of Nat. Biog.,” Vol XIII. p. 296; “Edin. Phil. Journal,” 1824, Vol. X. p. 185; “Cat. Sc. Papers Roy. Soc.,” Vol. I. pp. 58–61; Vol. VI. p. 565; Vol. VII. p. 29; “Bibl. Britan.,” Vol. XVI, N.S. p. 309; Vol. XVII, N.S. p. 16; Vol. XIX. p. 244; Vol. XX. pp. 173, 258; Vol. XXIV. p. 109.

For Le Chevalier Julius Konrad von Yelin (1771–1826), consult “Bibl. Britan.,” Vol. XXIII, N.S., 1823, p. 38; Vol. XXIV, N.S., 1823, p. 253, and, especially, the important tract on the discovery of thermo-magnetism at p. 31 of his “Die Akademie der Wissenschaften und ihre Gegner,” Munich, 1822.

=A.D. 1820.=--Arago (Dominique François Jean), famous French astronomer, physicist and statesman (1786–1853), who at the early age of twenty-three had, besides being Assistant Astronomer to the Observatory, become the successor both of Lalande in the Academy of Sciences and of Monge in the chair of analytical mathematics at the Polytechnic School, and who, conjointly with Gay-Lussac, had founded the highly valued _Annales de Chimie et de Physique_ in 1816, communicates to the French Institute, on the 25th of September 1820, his discovery that the electric current has the power of developing magnetism in iron and steel. Into the axis of a galvanic conductor made in the form of a coil, or helix, he placed a needle, the extremities of the wire coil being connected to the poles of a battery, and with this he proved that the wire not only acted on bodies already magnetized, but that it could develop magnetism in such as did not already possess the power. When soft iron was used, the magnetism given was only temporary, but on repeating the experiment, M. Arago succeeded completely in permanently magnetizing small steel needles. Arago’s paper on the subject appears at p. 94, Vol. XV of the _Ann. de Ch. et de Ph._, and it is said that at about the same time Dr. Thos. J. Seebeck (1770–1831), and Georg Friedrich Pohl (1788–1849) laid similar results before the Berlin Academy, also that Sir Humphry Davy independently made a like discovery, of which he advised Dr. Wollaston, Nov. 12, 1820. Reference to this fact has already been made at Davy, under date A.D. 1801, wherein it was stated that the latter had found iron filings to so adhere to the connecting wire as to form a mass ten or twelve times the thickness of the wire. This was also the case in the experiments of M. Arago, who, upon observing that the filings rose before coming in contact with the conjugate wire, drew the conclusion that each small piece of iron was converted into a temporary magnet. Thus was Arago led to the discovery of what is called magnetic induction by electric currents, or, in other words, that an electrical current passing through a conductor will induce magnetic action in such bodies near it as are capable of being magnetized (_Phil. Trans._ for 1821, p. 9; Tilloch’s _Jour. of Sci._, Vol. LVII. p. 42, 1821; eighth “Britannica,” Vol. VIII. p. 532 and Vol. XIV. p. 640; Thomas Thomson, “Outline of the Sciences,” p. 563).

A fact worth noting in connection with the development of Oersted’s discovery by both Arago and Ampère, is that in order “to prevent the communication of the electricity laterally in the folds of the coil, the wire was insulated by varnish in the first instance and afterward by winding silk or cotton around it” (F. C. Bakewell, “Elec. Sci.,” London, 1853, p. 37).

On the 22nd of November 1824, Arago announced to the French Academy of Sciences the remarkable discovery made by him of a new source of magnetism in rotatory motion. He was led to this by observing that when a magnetic needle was oscillating above or close by any body, such as water or a plate of metal, it gradually oscillated in arcs of less and less amplitude, as if it were standing in a resisting medium, and, besides, that the oscillations performed in a given time were the same in number (Humboldt’s “Cosmos,” “Magnetic Observations,” 1825). He caused a circular copper plate to revolve immediately beneath a magnetic needle or magnet, freely suspended so that the latter might rotate in a plane parallel to that of the copper plate, and he found that the needle tends to follow the circumvolution of the plate; that it will deviate from its true direction, and that by increasing the velocity of the plate the deviation will increase till the needle passes the opposite point, when it will continue to revolve, and at last with such rapidity that the eye will be unable to distinguish it. This, says Mrs. Somerville, is quite independent of the motion of the air, since it is the same if a pane of glass be interposed between the magnet and the copper. When the magnet and the plate are at rest, not the smallest effect, attractive, repulsive, or of any kind, can be perceived between them. In describing this phenomenon Arago states that it takes place not only with metals, but with all substances, although the intensity depends upon the kind of substance in motion.