The introduction of the electric spark for the purpose of volatilizing metals was an important step in the development of spectral analysis, but although used by both Wollaston and Fraunhofer its true value in that particular line was not realized for many years after their time.
Fraunhofer is not only celebrated as one of the founders of spectrum analysis, but he is well known also as the inventor of many important philosophical instruments, being the constructor of the great Dorpat parallactic telescope, called by Struve the giant refractor. It was during the year 1814 that he measured and described the innumerable dark lines of the solar spectrum known as Fraunhofer’s lines, which were first noticed by Wollaston and reported upon by the latter to the Royal Society in 1802.
References.—M. Merz, “Das Leben und Wirken Fraunhofers,” Landshut, 1865; Ninth “Encycl. Brit.,” Vol. IX. p. 727; “Abh. der K. Bayer, Akad. d. Wiss.” for 1814 and 1815; Fraunhofer’s biography in the “Memoirs of the Astronomical Society of London,” Vol. III. p. 117; his “Determination ...” München, 1819; Whewell, “Hist. of Ind. Sci.,” 1859, Vol. II. p. 475; Sci. Am., Nov. 19, 1887, p. 321; Phil. Trans. for 1814, pp. 204, 205, and for 1820, p. 95; Tyndall, “Heat as a Mode of Motion,” 1873, pp. 485, 486; article “Optics” in eighth “Encycl. Brit.,” Vol. XVI. pp. 544, 588, 591; Sir David Brewster’s article on “Electricity” in the “Encycl. Brit.”; “Mem. of the Roy. Bav. Acad. of Sci.” for 1822; “On the Spectrum of the Electric Arc,” in Jas. Dredge’s “Elec. Illum.,” Vol. I. pp. 32, 36; Edin. Trans., Vol. VIII for 1822; Edin. Jour. Sci., Vol. XIII. pp. 101, 251; Biblioth. Univ., Vol. VI. p. 21, as per Becquerel’s “Traité ...” Vol. I. p. 23; Dr. William A. Miller’s first and third lectures before the Royal Institution in 1867; Houzeau et Lancaster, “Bibl. Gén.,” Vol. II. p. 136; Rich. A. Proctor, “Old and New Astronomy,” 1892, p. 787.
A.D. 1815.—Bohnenberger (Johann Joseph Friedrich von), 1765–1831, Professor of Mathematics and of Astronomy at the Tübingen University, constructs an extremely sensitive electrometer by suspending a single strip of gold leaf upon a wire midway between, though apart from, the insulated terminating discs of De Luc’s column.
With this contrivance he found that, however slightly the leaf was electrified, it was drawn to one of the poles according to the nature of the electricity affecting it, and he was thus enabled to observe not only the presence of the slightest electrical influence, but the kind of electricity which was present.
Noad gives, at p. 30 of his “Manual,” an illustration of the electrometer as subsequently improved by Becquerel, and states that Mr. Sturgeon describes (“Lectures on Galvanism,” 1843) a somewhat similar arrangement, the delicacy of which he states to be such that the cap (plate) being of zinc and of the size of a sixpence, the pendant leaf is caused to lean toward the negative pole by merely pressing a plate of copper, also the size of a sixpence, upon it, and when the copper is suddenly lifted up the leaf strikes. The different electrical states of the inside and outside of various articles of clothing were readily ascertained by this delicate electroscope.
M. Gottlieb Christian Bohnenberger, of Neuenberg (1732–1807), is the author of several works treating particularly of the electrical machine, the electric spark, the electric doubler, etc., published at Stuttgart between 1784 and 1798.
References.—“La Grande Encyclopédie,” Vol. VII. p. 84; L. W. Gilbert, Annalen der Physik, Vols. XXIII (for Behrend’s); XLIX, LI (for “Beschreibung ... empfindlichen elektrometers ...”); Annales de Chimie et de Physique, Vol. XVI. p. 91; J. C. Poggendorff, “Biogr.-Liter. Handwörterbuch ...” Vol. I. p. 226; Sci. Am. Supp., No. 519, p. 8290, for Pouillet’s remarks upon the effectiveness of dry pile electroscopes; De la Rive, “Treatise on Electricity,” Vol. I. pp. 54–56.
A.D. 1815.—Mr. B. M. Forster sends to the Philosophical Magazine (Vol. XLVII. pp. 344–345) the description of an electrical instrument called “The Thunderstorm Alarum,” which can be made to show the effect produced by the passage of a charged cloud over an atmospherical electrometer.
He had several years before described, at p. 205 of the same publication, a method of fitting up in portable form one of De Luc’s electrical columns, respecting which latter he subsequently addressed communications, which appeared in Vols. XXXV. pp. 317, 399, 468; XXXVI. pp. 74, 317, 472; XXXVII. pp. 197, 265, also relative to one which he constructed and which ran continuously for five months.