=A.D. 1749.=--Duhamel (Henri Louis, du Monceau) (1700–1782), member of the French Royal Academy of Sciences, develops, in conjunction with M. Antheaulme, the method introduced by Gowin Knight (A.D. 1746) for making artificial magnets, which latter process was found to be defective when applied to very large bars. To Le Maire, however, is due (_Mem. de l’Acad. de Paris_, 1745 and 1750), the notable improvement which consists in magnetizing at the same time two steel bars of any shape by placing them parallel to each other and connecting their extremities, with pieces of soft iron placed at right angles, in order to form a closed rectangular parallelogram. Two strong magnets, or two bunches of small magnetic bars, with their similar poles together, are then applied to the centre of one of the bars to be magnetized and are drawn away from each other, practically as in Dr. Knight’s method, while being held at an inclination of about forty-five degrees. The operation is repeated upon the other bar and continued alternately until sufficient magnetism is imparted to both, it being borne in mind that before the treatment is given to the second bar the poles must in each instance be reversed, _i. e._ the pole which was to the right hand should be turned to the left. The entire operation is to be repeated upon the reverse side of both bars. 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.