SECT. XXIV. DISCOVERIES OF PROFESSOR MOSER. 219 



Another instance of these singular transformations may be 

 noticed. The pictures formed on cyanotype paper rendered more 

 sensitive by the addition of corrosive sublimate are blue on a 

 white ground and positive, that is, the lights and shadows are 

 the same as in nature, but, by the application of heat, the colour- 

 is changed from blue to brown, from positive to negative ; even 

 by keeping in darkness the blue colour is restored, as well as the 

 positive character. Sir John attributes this, as in the former 

 instance, to certain rays, which, regarded as rays of heat or light, 

 or of some influence sui generis accompanjdng the red and orange 

 rays of the spectrum, are also copiously emitted by bodies heated 

 short of redness. He thinks it probable that these invisible para- 

 thermic rays are the rays which radiate from molecule to mole- 

 cule in the interior of bodies, that they determine the discharge 

 of vegetable colours 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 objects of scientific discussion. 



The calorific and parathermic rays appear to be intimately 

 connected with the discoveries of Messrs. Draper and Moser. 

 Daguerre has shown that the action of light on the iodide of 

 silver renders it capable of condensing the vapour 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 

 discovery he announced in the following words : " If a surface 

 has been touched in any particular parts by any body, it acquires 

 the property of precipitating all vapours, and these adhere to it 

 or combine chemically with it on these spots differently from what 

 they do on the untouched parts." If we write on a plate of glass 

 or any smooth surface whatever with blotting-paper, a brush, or 

 anything else, and then clean it, the characters always reappear 

 if the plate or surface be breathed upon, and the same effect may 

 be produced even on the surface of mercury ; nor is absolute con~- 

 tact necessary. If a screen cut in a pattern be held over a polished 

 metallic surface at a small distance, and the whole breathed on, 

 after the vapour has evaporated so that no trace is left on the 

 surface, the pattern comes out when it is breathed on again. 



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