468 PROFESSOR LUDWIG MOSER ON LATENT LIGHT. 
particularly when employed in large quantities; but I succeeded 
in obtaining incontrovertible results in the following manner :— 
I dipped a small thermometer-bulb into distilled water and wrote 
upon a plate with the adhering drop, but so that the bulb itself 
did not touch. It is possible to perform the experiment so that 
the water is deposited on the plate in a concrete form only in 
some places, while it has passed over the greater part merely as 
a breath of vapour, which, however, is quite sufficient for these 
experiments. Or the trial may be made thus :—Strips of bibu- 
lous paper are fixed on to any convenient body and moistened 
with a very little distilled water; the polished surface is then 
touched for a moment with these strips, which is also quite suf- 
ficient. If, however, the evaporating liquid should leave some 
traces behind, as is generally the case with alcohol and ether, 
but in the case of water arises chiefly from the pulverulent mat- 
ters employed in the polishing, then these spots may be care- 
fully rubbed off. It is also as well to perform the operation 
under a damp cloth. After a silver plate has been exposed to 
the action of the evaporating water, alcohol, or ether, it is to be 
exposed to the vapours of water, mercury, iodine, or to those 
of hydrochloric acid, chloride, or bromide of iodine, &c.; in all 
cases a perfectly distinct picture is produced: in the aqueous 
vapours it is generally the strongest, in mercury it appears only 
after a long action, and in vapours of iodine it is often very faint. 
But even in this case it is only necessary to expose the plate to 
daylight in order to obtain a strongly marked image. If any 
other metals besides silver have been employed for evaporating 
the fluids, it is only necessary to expose them to any of the 
above-mentioned vapours in order to obtain good pictures. I 
will moreover mention, that if we allow hot water to evaporate 
from a Daguerre’s picture as it is taken out of the camera ob- 
scura, the image is completely destroyed. This is caused by a 
process of light, as will be seen from the following paragraphs. 
It is therefore evident that evaporation produces phaznomena 
similar to those of light, just as well as the condensation of va- 
pours; and I leave it for experimental philosophers to extend the 
result to the passage of a solid state of aggregation into a fluid 
one, and vice versd, and to take into consideration these trans- 
itions, both as refers to the processes of light and those of heat. 
As the matter is so new and of so much importance, I may be 
permitted to draw attention to the fact, that (remaining within 
