PHILOSOPHICAL SOCIETY OF WASHINGTON. 279 



nations of known phenomena, or to present old knowledge in a 

 new and more imposing dress, but to serve the higher purpose 

 of su"-<'-esting new experiments and new phenomena, and thus to 

 assist'^Tn enlarging the bounds of science, and extending the 

 power of mind over matter; and unless the hypothesis can be 

 employed in this way, however much ingenuity may have been 

 expended in its construction, it can only be considered as a scien- 

 tific roniance worse than useless, since it tends to satisfy the mind 

 with the semblance of truth, and thus to render truth itself less 

 an object of desire."* 



Light and Heat.—'Renvj also made important investigations 

 on some peculiar phenomena connected with light and_ heat. 

 For the purpose of experimenting on sun light he devised in 

 1840, a very simple form of heliostat, based on the suggestion 

 of Dr. Young, whereby the solar ray was received into an upper 

 Toomin a direction parallel to the earth's axis, requiring there- 

 fore only an equatorial movement of the reflector; which was 

 effected by the aid of a common cheap pocket watch placed on a 

 small hinged board set by a screw to the angle of latitude. The 

 mirror mounted on a swivel and properly balanced, presented 

 no sensible resistance to the running of the watch, which was 

 arranged for the 24 hour rotation by a watch-maker of Princeton. 

 The whole cost of the completed instrument (including the time- 

 movement) was but sixteen dollars. If any particular direction 

 of the ray was required, it was only necessary to place a stationary 

 mirror in the fixed path of the ray, adjusted to the desired 

 angle, f 



In 1841, on repeating experiments of Becquerel and Biot on 

 " Phosphorescence," he discovered some new characteristics in 

 the emanation (particularly when excited by electrical light) 

 which had not before been observed. J These were more fully 

 detailed in a communication made to the American Philosophical 

 Society, in 1843, "On Phosphorogenic Emanation.'' This phe- 

 nomenon had been first observed in the diamond, when taken into 

 a dark room immediately after exposure to direct sunlight, or 

 to a vivid electric spark ; and was afterward observed in several 

 other substances,— notably in the chloride of calcium—" Ilora- 

 berg's phosphorus. "§ It had also been shown by Becquerel that 



* Proceed. Am. PhU. Sor. Nov. 6, 1846, vol. iv. pp. 287-290. 



t Proceed. Am. Phil. Snc. S^^pt. 17, 1841, vol. ii. p. 97. 



J Proceed. Am. Phil. Soc. April 16, 1841, vol ii. p. 46. 



§ Homberg's phosphorus is chloride of caUiinra prepared by melting 

 one part of sal atnmonia with two parts of slaked lime. Canton's phos- 

 phorus is sulphide of calcium formed by a mixture of three parts of 

 sifted and calcined oyster shells, and one part of flowers of sulphur, ex- 

 posed for au hour to a strong heat. 



53 



