RADIATION OF CALORIC. 63 



8, and 9, Plate III., which he denominates the chromometer, 

 or colour- gauge. By adjusting the graduated wedges (filled as 

 to their transparent compartments with coloured liquids, of 

 red, yellow, and blue tints, perfectly conformable in density 

 with the coloured prismatic rays), he was enabled, by looking 

 through the eye-hole, to ascertain the precise quantity of each 

 coloured liquid necessary to produce perfect white transparent 

 light, and which on examination of the tabulated wedges he 

 found to be == 5 parts red, 3 parts yellow, and 8 parts blue ; 

 which, by experiments on his instruments, with which he 

 kindly accommodated me, I have confirmed by similar results. 



It would appear that the power of heating is greater in the 

 invisible rays outside the spectrum of the triangular prism, and 

 next to the red ray, and that in their ratio of intensity they may 

 be 70, lamp-black being 100. Sir H. Davy states those invis- 

 ible rays are capable of reflection as well as refraction, like the 

 other rays. 



The radiation of terrestrial matter producing heat was made 

 known by Del Cemento, Hooke, Scheele, and Pictet. The 

 opinion of Mr. Leslie, that the phenomena of the radiation of 

 terrestrial heat depends on certain pulsations or undulations of 

 the atmosphere capable of being reflected, but not of being 

 refracted, is stated to have been contradicted by the result of 

 the experiments on platina wire, by heat excited by a Voltaic 

 batteiy in a receiver exhausted to ^, by which it was found 

 a thermometer rose nearly three times as much as when it was 

 in its natural state of condensation. See Sir H. Davy, Ele- 

 ments of Philosophy, page 207. 



This appeared to be governed by the effect of pressure, the 

 cooling power of the rarefied air ; that is, its absorption of 

 caloric being much less in its rarefied than in its natural state. 



The colored bodies that absorb most light, and, of course, 

 reflect least, are the most heated when exposed to solar or ter- 

 restrial rays 1st black, 2nd red, 3rd green, 4th yellow, last, 

 white. 



