He also repeated the experiments of Davy on the light developed by charcoal points connected with a powerful galvanic battery, and found that this light was as effectual as solar light in decomposing muriate of silver and other bodies, and in acting upon hydrogen and chlorine gases, causing them to detonate, but he could not produce the same effect by the moon’s rays or by any other light.
The electricity developed in flame, which had received much attention from Paul Erman and others, was likewise investigated by Prof. Brande, whose conclusions are to be found detailed at Sec. III. chap. iii. part i. of the “Electricity” article in the “Encyclopædia Britannica.” Therein is recalled the fact that A. L. Lavoisier, P. S. Laplace and Aless. Volta previously obtained clear indications of electricity by the combustion of charcoal, while H. B. de Saussure failed to develop electricity either by the combustion or explosion of gunpowder, and Humphry Davy could not obtain it through the combustion of charcoal or of iron in air or in pure oxygen. In the above-named article will also be found an account of the investigations of Pouillet and of Becquerel in the same line; some of the other well-known scientists who have treated more or less directly upon the subject being E. F. Dutour, J. S. Waitz, J. J. Hemmer, Heinrich Buff, G. Gurney, Carlo Matteucci, W. R. Grove, Michael Faraday, M. A. Bancalari, W. G. Hankel, F. Zantedeschi and M. Neyreneuf.
References.—Phil. Mag., Vol. XLIV. p. 124; Phil. Mag. or Annals, Vol. IX. p. 237; Annales de Chimie, 5e série, Vol. II; Phil. Trans. for 1809 and 1820; Mémoires de Mathématiques, Vol. II. p. 246; “Cat. Sc. Pap. Roy. Soc.,” Vol. I. p. 48; “Bibl. Britan.,” Vol. LVII, 1814, p. 11.
A.D. 1813.—Colonel Mark Beaufoy (already alluded to at Graham, A.D. 1722), describes in the first volume of Dr. Thomas Thomson’s Annals of Philosophy what has by many been called the most perfect form known of the variation compass. It is also to be found illustrated at p. 81, Vol. XIV of the eighth “Britannica,” wherein it is said that he employed it in the valuable series of magnetic observations made by him between the years 1813 and 1821. It consists of a telescope, underneath the axis of which is a magnetic needle whose position is alterable in order to indicate the exact angle of deviation, or the declination of the needle from the true meridian.
Brewster states (eighth “Brit.,” Vol. XIV. p. 54) that when the diurnal variation of the needle was first discovered it was supposed to have only two changes in its movements during the day. About 7 a.m. its north end began to deviate to the west, and about 2 p.m. it reached its maximum westerly deviation. It then returned to the eastward to its first position, and remained stationary till it again resumed its westerly course in the following morning. When magnetic observations became more accurate, it was found that the diurnal movement commences much earlier than 7 a.m., but its motion is to the east. At 7.30 a.m. it reaches its greatest easterly deviation, and then begins its movement to the west till 2 p.m. It then returns to the eastward till the evening, when it has again a slight westerly motion; and in the course of the night, or early in the morning, it reaches the point from which it set out twenty-four hours before. The most accurate observations made in England were those of Colonel Beaufoy, when the variation was about 24½´ west. In these the absolute maxima were earlier than in Canton’s observations, and the second maximum west about 11 p.m. Dr. Thomas Thomson alludes to the diurnal investigations of Barlow and Christie and others, and gives (“Outline of the Sciences,” London, 1830, pp. 543–550) a table of the mean monthly variation of the compass from April 1817 to March 1819 as determined by Colonel Beaufoy. Mr. Peter Barlow, he says, has given in his “Essay on Magnetic Attractions” a very ingenious and plausible explanation of the daily variation by supposing the sun to possess a certain magnetic action on the needle.
References.—Phil. Mag., Vol. LIII, 1819, p. 387; LV, 1820, p. 394; W. S. Harris, “Rud. Mag.,” Parts I, II, pp. 150–152; “Encycl. Metrop.,” Vol. III (Magnetism), pp. 766, 767; Annals of Phil., series 1, Vols. II, VI, IX, XVI, and N.S., Vol. I. p. 94, for Beaufoy’s own summary of all his observations.
A.D. 1814.—Mr. Thomas Howldy addresses to the Philosophical Magazine a letter, dated Hereford, March 24, 1814, relative to “Experiments evincing the influence of atmospheric moisture on an electric column composed of 1000 discs of zinc and silver,” wherein he also makes reference to the dry pile of J. A. De Luc alluded to at A.D. 1809.
References.—Phil. Mag., Vol. XLIII. pp. 241, 363, and Nicholson’s Journal, Vol. XXXV. p. 84; also the Phil. Mag., Vol. XLI. p. 393, for a description of the electric column of 20,000 pairs of zinc and silver plates, and others, constructed during the previous year (1813) by Mr. George J. Singer.
The above-named letter was followed (Phil. Mag., Vols. XLVI. pp. 401–408, and XLVII. p. 285) by a communication on the “Franklinian Theory of the Leyden Jar ... with Some Remarks on Mr. Donovan’s Experiments,” and by another letter sent to MM. R. Taylor and R. Phillips (Phil. Mag. or Annals, Vol. I. p. 343) relative to the paper of William Sturgeon “On the Inflammation of Gunpowder by Electricity,” which appeared at p. 20 of the last-named book.
An interchange of correspondence not long since through the columns of the London Electrical Review, for the purpose of ascertaining the period of the earliest use of carbon as a resistant, brought forth an extract from the “Treatise on Atmospheric Electricity,” published at London and Edinburgh, 1830, by Mr. John Murray, of Glasgow, which reads as follows: “Mr. Howldy, of Hereford, an ingenious electrician, has by some novel experiments clearly proved the increased power of electricity if retarded in its progress; instead of using tubes of glass filled with water, as Mr. Woodward had done, he has employed a glass tube supplied with lamp black.”