[Annals X. Y. Acap. Sci., XT, Xo. 17, pp. 401 to 403, October 13, 1898.] 



A SIMPLE AND CONVENIENT PHOSPHOROSCOPE. 

 Wallace Goold Levison. 



(Read April 4, 1898.) 



In Wright's UgJit^ there is a description of a phosphoroscope 

 designed for lecture illustration which is attributed to Professor 

 John Tyndall. It consists of a cylinder set in revolution by a 

 crank mechanism before a slit in a light-tight box, through 

 which the light from an electric arc lamp enclosed in the box 

 falls upon the cylinder. The cylinder being coated with 

 coarsely pulverized uranium glass, the audience, in a dark room 

 observes a band of green light across the cylinder the inten- 

 sity of which increases in proportion to the rapidity of its revolu- 

 tion. This is due to light absorbed by the uranium glass as it 

 passes the slit, and given forth so deliberately as to be still es- 

 caping during the time required for more than a half revolution 

 of the cylinder. 



Having occasion to use some such simple contrivance in a 

 recent investigation upon this property ^ of minerals, I con- 

 structed a modified form of this instrument consisting of a hol- 

 low pasteboard cylinder, set in revolution by an electromotor, 

 whereby much greater speed is attained than by a mechanical 

 device. Instead of coating the cylinder directly with the min- 

 eral to be examined I dust it in coarse or fine powder upon the 

 surface of sheets of paper brushed over with hot gelatine. 

 These fold around the cylinder and fasten with rubber bands, 

 and are, therefore, interchangeable at pleasure. In other cases 

 I simply fix a single piece of a mineral, either transparent or 

 opaque, upon the surface of the cylinder. At the great speed 



1 Wright (L.), Light, London, 1882. 



2 For which the term photofluorescence, in view of the recent experiments of 

 Wiedemann and Schmidt seems to me best adapted. 



(401) 



