References.—Harris, “Rudim. Magn.,” I. and II. pp. 85 and 86; P. Larousse, “Dict. Univ.,” Vol. VI. p. 1363; “Biog. Générale,” Vol. XV. pp. 106–107; Condorcet, “Eloge de Duhamel”; I. M. Des Essarts, “Siècles littéraires”; Georges Cuvier, “Hist. des Sc. Naturelles,” Vol. V; Thos. Thomson, “Hist. of the Roy. Soc.,” London, 1812, p. 45.
A.D. 1750–1753.—In M. Arago’s “Historical Eloge of James Watt,” translated by James P. Muirhead and published in London during the year 1839, it is said, at p. 6, that Watt constructed, at about the period first mentioned herein, a small electrical (his earliest) machine, the brilliant sparks from which became a subject of much amusement and surprise to all the companions of the poor invalid (“James Watt,” by Andrew Carnegie, New York, 1905).
A.D. 1750.—Wargentin (Pierre Guillaume—Perh Vilhelm—) (1717–1783), Secretary to the Swedish Academy of Sciences and a distinguished astronomer, addresses, on the 21st of February, a letter to the Royal Society, of which a copy is to be found in Vol. XLVII. p. 126 of the Phil. Trans. In this he gives his observations of the result produced on the magnetic needle by the aurora borealis.
We have already seen (under the A.D. 1683 date), that the discovery of the fact that magnets are affected by the polar lights has been ascribed to Wargentin, and we have also learned (A.D. 1722) that he ascertained the diurnal changes of the magnetic needle with more precision than had been done by George Graham.
References.—Walker, “Magnetism,” p. 116; American Journal Science and Arts, 1841, Vol. XXX. p. 227; Celsius, A.D. 1740, and the abridgments of Hutton, Vol. X. p. 165.
A.D. 1750.—Michell (John), an eminent English man of science, Professor at Queens’ College, Cambridge, publishes “A treatise of Artificial Magnets, in which is shown an easy and expeditious method of making them superior to the best natural ones.”
The process introduced by this work is known as that of the “double touch.” This consists in first joining, at about a quarter of an inch distance, two bundles of strongly magnetized bars, having their opposite poles together, and in drawing these bars backward and forward upon and along the entire length of the bars to be magnetized, which latter have already been laid down end to end and in a straight line. The operation is to be repeated upon each side of the bars. The central bars of a series thus acquire at first a higher degree of magnetism than do the outer ones, but by transposing the latter and treating all alike the magnetic virtue is evenly distributed. In this process the external bars act the same part as do the pieces of soft iron employed in the Duhamel method.
At Chap. VI. p. 20 of the third volume of his “Rudimentary Magnetism,” Harris thus expresses himself: “Michell advanced the idea that in all the experiments of Hauksbee, Dr. Brooke Taylor, William Whiston and Musschenbroek, the force may really be in the inverse duplicate ratio of the distances, proper allowance being made for the disturbing changes in the magnetic forces so inseparable from the nature of the experiment. He is hence led to conclude that the true law of the force is identical with that of gravity, although he does not set it down as certain.”
References.—Harris, “Rud. Mag.,” I. and II. pp. 94–95; C. R. Weld, “Hist. Roy. Soc.,” Vol. I. p. 512; Phil. Trans., Vol. LI. pp. 390, 393, and Hutton’s abridgment, Vol. XI. p. 418; Gaugain’s observations in “Sc. Am. Suppl.,” No. 7, p. 99.
A.D. 1750.—Boulanger—not Boullangère—(Nicholas Antoine) (1722–1759), a well-known French writer, whose extensive studies were interrupted by his death, in 1759, at the early age of thirty-seven, gives, in this “Traité de la cause et des phénomènes de l’électricité,” accounts of many important observations made in the electrical field.