\Q4< ON LIGHT. 



place my points in a cylindrical wire, terminated by fmooth 

 wooden balls, whofe femidiameler is lefs than the length of 

 the points: This wire is moveable on its axis, by means of a 

 fpring focket annexed to the Item which enters the conductor: 

 The points may of courfe be placed at any required elevation, 

 and the greateft intensity any variation in their fituation pro- 

 duces, be obtained. When the points are elevated a little 

 above the horizontal line, the danger of fcratching the glafs 

 is effectually prevented, by the balls coming in contact while 

 the points are kept at a fmall diftance. The fecurity this 

 application produces, and the additional intenfity it affords, 

 have induced me to trouble you with this communication. 

 I am, 



Dear Sir, 



Your's, &c. 



G. J. SINGER. 



VII. 



Quefiion whether Light as a Body may not have its Temperature, 

 raifed or lowered, and produce the Effects afcribed to refiecled 

 Heat. By J. P. 



To Mr. NICHOLSON. 

 SIR, 



Queftion re- Jt OSSESSING no differential thermometer, nor any time to> 



fpeding light. em p] y j^ J cannot prove whether my opinion is well founded 



or not, refpecling the ingenious experiments of Mr. Leilie or 



of M. Pi&et, by which the reflection of invifible (not radiant) 



heat, and even of cold, appears to have been proved. 



Initead of there being an actual reflection of heat as a fub- 

 ftance, or of cold as a fubftance, is it not in all thefe cafes 

 a reflection of heated or of cooled light ? In the experiments 

 with the heated cannifter, the light of the room is, I doubt 

 not, heated by the cannifter; and if collected in a focus, muff, 

 produce an effect on the thermometer, anfwerable to the in,- 

 creafed quantity of heat with which it is impregnated. Thus 

 alfo in Monf. Pictet's experiment, the light intercepted by the 

 mirror and thence reflected, has been deprived of a portion 

 of its caloric, or in other words cooled, by the ice ; at the 



focal 



