50 REPORT—1848, . 
CHEMISTRY. 
On the Action of the Red, Orange and Yellow Rays upon Iodized and Bromo- 
iodized Silver Plates after they have been affected by daylight, and other 
Phenomena of Photography. By A. Crauper. 
Ir was shown by M. E. Becquerel, that the light which permeates red and yellow 
glasses had the property of continuing on a Daguerreotype plate the action of the 
light which causes the condensation of mercurial vapour on the surface. This pro- 
perty being in contradiction to that announced by Mr. Claudet when operating par- 
ticularly with bromo-iodide of silver, he made some new experiments which com- 
pletely confirmed the first, but showing at the same time the correctness of the fact 
discovered by M. E. Becquerel, as far as the action relates to a certain coating of 
iodine. : 
M. Gaudin, experimenting on the discovery of M. E. Becquerel, had found that 
red and yellow glasses not only continued the effect produced by light, but that 
an image might be developed under their influence without the action of mercury. — 
Investigations on these various subjects have enabled Mr. Claudet to discover that 
light alone also produces an image without mercury, quite similar to that obtained 
by M. Gaudin with the second action of red or yellow glasses. This curious fact, 
which had escaped Daguerre and all his followers, affords to Mr. Claudet a means 
of offering an explanation of the phenomena elucidated by M. E. Becquerel, and 
proposing a new theory of the formation of the Daguerreotype image. 
Mr. Claudet thinks that the image produced by light alone is due to the decom- 
position of the iodide of silver, by which silver is precipitated on the surface in a 
finely divided powder or crystals, producing an effect similar to that caused by the 
condensation of mercurial vapour. 
The red or yellow rays having a photographic action of their own, very slow on thé 
non-affected parts, but capable of operating more strongly on the parts already affected 
by white light, continue that precipitation of finely divided silver, and when the ac- 
tion of the red or yellow rays is added to the condensation of mercurial vapour, it 
doubles the effect by which the image appears visible. This would explain the ac- 
tion called continuation by M. E. Becquerel, as well as the phenomenon of the image 
developed by the red or yellow glasses according to M. Gaudin’s discovery; the 
only difference being that M. Gaudin continues the action of the red or yellow rays 
until they have fully and visibly determined the precipitation of the silver. 
Mr. Claudet concluded by stating, that he had been able to ascertain that the pure 
light of the sun can produce on the surface of bromo-iodide of silver the change of 
modification by which it acquires the affinity for mercurial vapour in the incredible 
short space of time of about +2,5th part of a second. 
On the Laws of Chemical Combinations and the Volumes of Gaseous Bodies. 
By the Rev. Tuomas Extey, M.A. 
Were we acquainted with the laws of force at minute distances, as we are with 
gravitation, the grand difficulty respecting chemical combinations would be over 
come; but while these laws remain unknown the subject will remain in its present 
state, involved in a labyrinth. It has been of late too much the fashion to discard 
hypotheses. Newton discovered the law of gravitation; but how? by first admit- 
ting it hypothetically, and then testing the hypothesis by calculation. Newton failed 
to assign the laws of force at very small distances; he carried the law of gravitation 
to a limit near the centre of an atom, and concluded from phenomena which he 
observed, that there follow several spheres of force alternately attracting and re- 
pelling. So long as the laws of these forces remain unknown, no true theory can 
be established. It is therefore best to assign some hypothesis which fixes some pro- 
bable law of force, and then to calculate the effects; the author assumes nothing 
more than that the force of gravitation is continued to the centre of atoms, and that 
it acts outwardly in a small central sphere, constituting a small sphere of repulsion : 
