“In explanation and justification of this discouraging judgment from so high an authority in magnetics, it must be remembered that both in the galvanometer and in the electro-magnet, the coil best calculated to produce large effects was that of least resistance; which unfortunately was not that best adapted to a long circuit. On the other hand the most efficient magnet or galvanometer was not found to be improved in result by increasing the number of galvanic elements. Barlow in his inquiry as to the law of diminution was led (erroneously) to regard the resistance of the conducting wire as increasing in the ratio of the square root of its length” (pp. 110, 111 of the last-cited “Journal.)”]
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.”