183 THERMOGRAPHY. 



The same thing occurs with chromate of silver, some 

 of the salts of mercury, argentine preparations combined 

 with protosulphate of iron or gallic acid, and some other 

 chemical combinations. These progressive influences 

 point to some law not yet discovered, which seems to 

 link tin's radiant actinism with the chemical agent exist- 

 ing in all matter. 



This problem also connects itself with another class of 

 facts which, although due, in all probability, to a great 

 extent, to calorific radiations, and hence known under 

 the general term of Thermography, appear to involve 

 both chemical and electrical excitation. From the in- 

 vestigations of Moser and of others, we learn the very 

 extraordinary fact, that even inanimate masses act and 

 react upon each other by the influence of some dark 

 radiations, and seem to exchange some of the peculiari- 

 ties which they possess. This appears generally in the 

 curious experiments which have been referred to, as con- 

 fined merely to form or structure. Thus an engraved 

 plate will give to a polished surface of metal or glass 

 placed, near it, after a very little time, a neat distinct 

 image of itself; that is, produce such a structural dis- 

 turbance as will occasion the plate to receive vapour dif- 

 ferently over those spaces opposite to the parts in cameo 

 or in intaglio, from what it does over the opposite. If a 

 piece of wood is used instead of a medal, there will, by 

 similar treatment, be produced a true picture of the wood, 

 even to the representation of its fibres.* 



and by quite insensible gradations to positive, and the shades ex- 

 hibiting a most singular chatoyant change of colour from ruddy - 

 "brown to black, when held more or less obliquely. No doubt, also, 

 gold pictures with the metallic lustre might be obtained by the 

 same process, though I have not tried the experiment." 



* The details of this curious subject may be studied in the 

 following memoir and communications: On vision and the action 

 of light on all bodies: by Professor Ludwig Moser, of Konigsberg ; 

 from Poggendorff's Annalen, vol. Ivi. p. 177, No. 6, 1845. Svme 

 remarks on Invisible Light: by Professor Ludwig Moser, of 



