SKCT. XXV. CONCLUSIONS TO BE DRAWN. 233 



of these rays, not their light, which operates the 

 change ; 2dly. That this heat possesses a peculiar 

 chemical quality which is not possessed by the purely 

 calorific rays outside of the visible spectrum, though far 

 more intense ; and, 3dly. That the heat radiated from 

 obscurely hot iron, abounds especially in rays analogous 

 to those of the region of the spectrum above indicated. 



Another instance of these singular transformations 

 may be noticed. The pictures formed on cyanotype 

 paper, rendered more sensitive by the addition of cor- 

 rosive sublimate, are blue on a white ground and posi- 

 tive, that is, the lights and shadows are the same as in 

 nature, but by the application of heat, the color is 

 changed from blue to brown, from positive to negative ; 

 even by keeping in darkness the blue color is restored, 

 as well as the positive character. Sir John attributes 

 this as in the former instance to certain rays, which re- 

 garded as rays of heat or light, or of some influence sui 

 generis accompanying the red and orange rays of the 

 spectrum, are also copiously emitted by bodies heated 

 short of redness. He thinks it probable that these in- 

 visible parathermic rays are the rays which radiate 

 from molecule to molecule in the interior of bodies, that 

 they determine the discharge of vegetable colors at the 

 boiling temperature, and also the innumerable atomic 

 transformations of organic bodies which take place at 

 the temperature below redness, that they are distinct 

 from' those of pure heat, and that they are sufficiently 

 identified by these characters to become legitimate ob- 

 jects of scientific discussion. 



The calorific and parathermic rays appear to be so 

 intimately connected with the discoveries of Messrs. 

 Draper and Moser that the subject of solar radiation 

 would be imperfect were they omitted. The dis- 

 covery of Daguerre shows that the action of light on 

 the iodide of silver renders it capable of condensing the 

 vapor of mercury which adheres to the parts affected 

 by it. Professor Moser of KOnigsberg has proved that 

 the same effect is produced by the simple contact of 

 bodies, and even by their very near juxta-position, and 

 that in total darkness as well as in light. This dis- 

 covery he announced in the following words : " If a 

 u2 



