Noad states (“Manual,” London, 1859, p. 580) that Lambert’s deductions were confirmed twenty years later by Coulomb, through the agency of his delicate torsion balance, and more recently (about the year 1817) by Prof. Hansteen, of Christiania.
Previous to the above-named date, in 1760, Lambert had published, both at Leipzig and at Augsburg, his “Photometria, sive de Mensura et Gradibus Luminis, Colorum et Umbræ,” the sequel to a tract printed two years before, wherein he indicates the mode of measuring the intensity of the light of various bodies. The celebrated mathematician and astronomer, Pierre Bouguer (1698–1758), who had published, in 1729, his “Essai d’Optique,” etc., which was greatly enlarged in his “Traité,” etc., brought out by La Caille in 1760, may be considered the founder of this branch of the science of optics, to which the name photometry has been given by English writers. The photometer designed by Sir Benjamin Thompson, Count Rumford (entered at A.D. 1802), has been described in Phil. Trans. for 1794, Vol. LXVII. His method is to cast two shadows of a given object near each other on the same surface, the lights being removed to such distances that the shadows appear equally dark.
References.—Sir John Leslie’s “Fifth Dissertation” in the eighth “Encycl. Brit.”; Count Rumford’s photometer illustrated at Plate XXVII. figs. 387, 388, vol. i. of Dr. Thomas Young’s “Course of Lectures,” London, 1807; also Vol. II. pp. 282 and 351 of the same work, concerning photometry generally; Dredge and others, “Electric Illumination,” etc. (chiefly compiled from London Engineering), Vol. II. pp. 101–117; Brewster’s “Edin. Jour. of Sc.,” 1826, Vol. II. p. 321; Vol. III. p. 104; Vol. V. p. 139, for William Ritchie’s articles on the photometer of Mr. Leslie, and relative to an improved instrument upon the principles of Bouguer (Edin. Transactions, Vol. X. part. ii.); Lambert’s biography and the article “Magnetism” in the “Encycl. Brit.”; Harris, “Rudim. Magn.,” Part III. pp. 20, 33, 191–203.
It may be added that all the valuable manuscripts left by Lambert were purchased by the Berlin Academy, and were afterward published by John Bernoulli, a grandson of the celebrated John Bernoulli alluded to at A.D. 1700.
A.D. 1766.—Lullin (Amadeus), in his “Dissertatio physica de electricitate,” Geneva, 1766, at p. 26, alludes to Beccaria’s experiments, saying that he produced much greater effects with the electric spark by passing the latter through oil instead of water: oil being a much worse conductor, the spark in it is larger. At p. 38 of the same work he details the experiments made to prove the correctness of Mollet’s doctrine regarding the constant motion of electrical atmospheres, and at p. 42 are given his experiments to show the production of electricity in the clouds. With a long insulated pole projecting from the mountain side he observed, among other effects, that when small clouds of vapour produced by the sun’s heat touched only the end of the pole the latter was electrified, but that it was not affected if the entire pole was covered by the vapour (“Lib. Useful Knowledge,” “Electricity,” Chap. XI. Nos. 154, etc.).
Lullin, it is said, proposed a modification of Reusser’s plan of telegraphing, in manner stated at p. 69 of Reid’s 1887 “Telegraph in America.”
A.D. 1766.—L’Abbé Poncelet, a native of Verdun, France, publishes at Paris “La Nature dans la formation du Tonnerre,” etc., wherein he indicates a method of protecting from lightning residences, pavilions and other structures, by constructing them of resinous woods and lining them with either silk or waxed cloths. He quaintly remarks that as they thus present “on all sides resinous surfaces, which never receive phlogiston by communication, the latter (thunder and lightning), after having leaped lightly around the pavilion and finding itself unable to attack it, will probably depart in order to pursue its ravages elsewhere.”
References.—Scientific American Supplement, No. 66, p. 1053, for a copy of the frontispiece of the above-named work; also Figuier, “Exposition et Histoire,” etc., 1857, Vol. IV. pp. 234, 235.
A.D. 1767.—Bozolus (Joseph), an Italian Jesuit, Professor of Natural Philosophy at Rome, is the first (and not Cavallo, A.D. 1775) to suggest employing the active principle of the Leyden jar for the transmission of intelligence.
His plan is to place underground two wires which are to be brought at each station close enough to admit of the passage of a spark. One of the wires is to be connected with the inner coating and the other with the outer surface of a Leyden phial; the sparks observed at the opening between the wires being there made to express any meaning according to a preconcerted code of signals.