344 
POPULAR SCIENCE REVIEW. 
brought in contact -with them, are likewise incapable of receiving latent 
images. But these capacities may exist conjointly, as we see in the case of 
large numbers of silver compounds. This new theory rests upon these facts, 
namely, the sensibility to light of pure iodide of silver and the spontaneous 
resensilising of pure iodide of silver, and will, as Mr. Carey Lea believes, 
(( dispel all the mystery that has seemed to some to envelope the idea of a 
physical image and bring all the most obscure facts of photo-chemistry into 
parallelism with well understood and very simple phenomena.” We quote 
from the British Journal of Photography, in which, unless we are much 
mistaken, similar views were put forth some time since.* 
A New Camera has been introduced in America for producing simul- 
taneously any number of portraits of a sitter with one lens. This is ob- 
tained by the adjustment of a number of movable mirrors fastened on 
blocks of wood and so contrived as to throw the reflected images each on the 
proper part of the plate or focussing screen. 
PHYSICS. 
The Physics of Chemical Reaction. — According to the researches of M. 
Berthelot, a chemical reaction, which is capable of setting free an appreciable 
quantity of heat, will always accompany the following conditions : — 1. The 
reaction is one which reaches its limit within a very short time from its 
commencement ; this condition is fundamental. 2. The reaction is one 
which begins without foreign aid at the temperature of the commencement 
of the experiment ; reactions excluded by this condition act in conformity 
with the principle enunciated if they are caused to set in either by raising 
the temperature or by other means. 3. The parent substances and the 
products possess similar functions. He is of opinion that the inverse re- 
actions of iodhydric acid and argentic chloride might be foreseen from the 
basis of this general principle, and that the analogous action of iodhydric 
acid on potassic chloride, which he has experimentally verified, is a further 
proof of the correctness of his view. — Vide Chemical Neivs. 
A 11 Standard” Spectrum, which promises to be exceedingly useful, and 
* Since the above was written, Mr. W. H. Harrison has written to the 
paper in which Mr. Lea’s articles appear, expressing u unbounded astonish- 
ment ” to find that gentleman republishing his ideas as new ones of his own, 
without any alteration whatever, except a guess, unsupported by experiment, 
11 that the moving molecules vibrate with a motion which throws off chemical 
rays.” Both Mr. Lea and Mr. Harrison have long been constant contribu- 
tors to the British Journal of Photography, in which the papers on u The 
Mechanical Action of Light,” to which the latter gentleman alludes, were 
published not longer ago than last autumn. Our own impression is that 
these ideas were published long before either Mr. Lea or Mr. Harrison ad- 
vanced them in Hunt’s (C Researches,” but between this and our next issue 
we shall give the matter further attention. 
