Angstrom asserted that he observed the auroral line in the spectrum of the zodiacal light, and Lewis saw the latter during the aurora of May 2, 1877. Humboldt, who observed it (“Cosmos,” 1849, Vol. I. p. 126) in the Andes at an elevation of 13,000 to 15,000 feet, as well as on “the boundless grassy plains, the Llanos of Venezuela, and on the seashore, beneath the ever-clear sky of Cumana,” believes it to be caused by “a very compressed annulus of nebulous matter, revolving freely in space between the orbits of Venus and Mars.” In this connection he refers to Arago in the _Annuaire_ for 1832, p. 246, and to a letter published in _Comptes Rendus_, XVI, 1843, p. 687, from which the following is extracted: “Several physical facts appear to indicate that, in a mechanical separation of matter into its smallest particles, if the mass be very small in relation to the surface, the electrical tension may increase sufficiently for the production of light and heat.” In Chambers’ “Descript. Astronomy,” p. 257, the historian Nicephorus is credited with first calling attention to the existence of this phenomenon, to which Giovanni Domenico Cassini gave the name of Zodiacal Light, after determining its relations in space during the year 1683 (_Mém. de l’Académie_, 1730, Tome VIII. pp. 188 and 276), but to Childrey belongs the credit of having given to Europe the first explicit description of this phenomenon at p. 183 of his 1661 “Britannia Baconica.” REFERENCES.--Sturgeon’s _Annals_, etc., Vol. II. pp. 140–142; Prof. C. W. Prichett’s paper in _Sci. Am. Supp._, No. 126, p. 2008, and the conclusions reached by Herr Gronemann (_Archives Néerlandaises_) in _Sci. Am. Supp._, No. 327, p. 5221; Whewell, “Hist. of the Ind. Sciences,” 1859, Vol. I. p. 531, and Vol. II. p. 609; Tyndall, “Heat as a Mode of Motion,” 1873, pp. 57, 58, 497, 498; J. F. J. Schmidt, “Das Zodiacallicht,” Braunschweig, 1856; the very interesting abstract given in “The Journal of the Brit. Assoc.,” Vol. XII. No. 5, of paper read by Rev. J. T. W. Claridge, F.R.S., Jan. 9, 1902; Houzeau et Lancaster, “Bibl. Générale,” Vol. II. 1882, pp. 763–771; “Pr. Roy. Soc. of Edin.,” XX. pt. 3; C. Wilkes, “Theory of Zod. Light,” Philad., 1857; _Phil. Trans._, Vol. XXXVIII. p. 249; “Cosmos,” 1849, Vol. I. pp. 126–134; “Anc. Mém. de Paris,” I, VIII and X; J. J. de Mairan, Paris, 1733; “U. S. Japan Expedition,” Vol. III, Washington, 1856.