465 
ARTICLE XVIII. 
On the Power which Light possesses of becoming Latent. By 
Professor Lupwie Moser of Kénigsberg. 
[From Poggendorff’s Annalen, Band lvii. 1842. No. 9. p. 1.] 
IN the following I intend to prove that there is a Latent Light 
as well as a Latent Heat; that they both are produced under 
similar circumstances, and when under the same influences pass 
into a free state; and that when a body alters its state of aggre- 
gation we cannot any longer regard this as produced by heat 
alone; light also takes an active part in the process. I certainly 
must require the same favour to be shown to latent light as has 
long since been granted to latent heat, viz. to allow the question, 
as to what idea we can have of such a state, to remain unan- 
swered. Since Deluc and Black discovered latent heat in the 
middle of the last century, nothing has been done to render this 
extraordinary power comprehensible, and yet the fact has not 
been denied on this account. I hope, therefore, that the incom- 
prehensible nature of a combined state of light will not be ad- 
duced as an argument for its non-existence; the proofs in both 
cases are equally convincing. The peculiar nature of light, which 
does not allow of a determination of its intensity, also prevents 
a quantitative measurement in the case of light which has become 
latent. On the other hand, however, I believe I shall be able 
to extend the knowledge of this latter to such a degree as has 
not yet been done with latent heat, and which, even since the 
great discoveries of Melloni, will not very speedily be achieved. 
In my treatise on Vision, &c., I have shown that the precipi- 
tation of vapours exerts an influence on the condensing bodies 
similar to that of light; but at present a new definition of this 
agent is necessary, for, since I have proved the existence of in- 
visible rays of light, the retina has ceased to furnish us with the 
most striking proofs. The most general definition which I 
should be inclined to propose for the present is, that by light 
the surfaces of ail bodies are modified, so that they condense va- 
pours otherwise than usual. A plate of iodized silver, which has 
undergone the action of light in a camera obscura, and has after- 
