Intelligence and Miscellancous Articles. 325 
of a living animal, which, as is well known, are always impregnated 
with organic matters known under the name of grease (swint). 
« 3. When you raise the temperature of the body forming an 
image, that of the polished surface remaining the same, the image 
is formed in a very short time. 
«©4. When a polished surface has received the image of a body, 
this same surface, placed very near a second polished surface, is ca- 
pable of forming in its turn an image which may be called secondary, 
and which itself might form tertiary images, if the perfection of the 
impression did not diminish very quickly by these successive transfers. 
«5, When a very thin lamina of mica was interposed between the 
body forming the image and the polished surface, I have constantly 
found that the action was null. However, in certain circumstances 
images are thus obtained which it is of importance not to confound 
with those that the body itself would have produced; such is the 
case when the same lamina of mica, serving for two consecutive 
trials, is placed in the second trial in a position the reverse of that 
which it had occupied in the first; then the surface of mica which 
during the first experiment has been in contact with the image- 
forming body and has thus received an impression, will be in con- 
tact with the polished surface during the second, and must thence 
produce a secondary image. This image may always be distin- 
guished from the direct image, inasmuch as this is evidently a sym- 
metrical representation of the surface of the body, whilst the secon- 
dary image being symmetrical, with respect to the preceding one, is 
found to be an identical representation of the body. 
“6. Lastly, the different experiments relative to these images 
have absolutely the same results, whether we operate under the in- 
fluence of the light or of total darkness.”’ 
Extract from a Letter from M. Knorr, communicated by M. Breguet. 
Comptes Rendus, Feb. 13, 1843, p. 398. 
“ I have been engaged for these four weeks in following up the 
discoveries of M. Moser of Keenigsberg upon invisible light; and 
haye read a short memoir which I had written on the subject at the 
meeting of our Philosophical Society the 7th (19th) November 1842. 
I merely related new facts which I had discovered without entering 
into theoretical speculations, but I believe these facts sufficiently 
prove that all the actions which Moser attributes to invisible light 
owe their origin to heat. I have also created an art entirely new, which 
I have named thermography ; for I have found that visible images can 
be obtained without any condensation of vapour on the plates, merely 
by the action of heat. There are three different methods for this : 
by the first, images may be obtained in from 8 to 15 seconds, but 
not with constant success; the second seems applicable only to bodies 
that are not very good conductors of heat; the third deserves the 
preference, as ensuring better and almost universal success, but it re- 
quires from 8 to 10 minutes to obtain an image. ‘Thus I have re- 
ceived proofs of coins of platinum, gold, silver, engraved plates of 
copper and brass, engraved stones, steel and glass, also of engravings 
printed on common paper; the images were formed on plates of 
silvered copper, pure copper, steel and brass.” 
