222 4] 
XXIII. 
ON THE INFLUENCES OF TEMPERATURE UPON THE 
SENSITIVENESS OF THE PHOTOGRAPHIC DRY 
PLATE. By J. JOLY, D.Sc., F.R.S. 
[Read DucremBer 20; Received for Publication DeczmBER 22, 1893 ; Published 
Frpruary 17, 1894.] 
Tue fact that a photographic plate loses in sensitiveness at low 
temperatures has already been the subject of experiment. But I 
am not aware of any experiments beyond those of Abney and 
Dewar, which were, so far as I can learn, confined to exhibiting 
the broad fact of the loss of sensibility. Many practical photo- 
graphers have also, I believe, been aware of the fact from every-day 
observation. 
Some couple of months ago, being then in ignorance of previous 
observations on the subject, I made experiments upon an Edwards’ 
isochromatic plate and upon a Wratten fast plate. The sensitive 
plate was backed, one-half with a poultice of solid carbonic acid, 
just made into a paste with ether; the other half with a poultice 
of hot water in flannel. It was, in this state of unequal heating, 
exposed behind a double layer of thick plate-glass to a gas flame. — 
Upon development, the cold half showed but little light-action ; 
the hot was strongly affected. The double window of plate- 
glass is essential to keep moisture from depositing and obscuring 
the cold half. A thin piece of glass is cooled so quickly that it 
obscures before there is time to expose it. The naked plate 
rapidly becomes frosted on the cold half. 
In this experiment I observed that the effect was more 
marked upon the isochromatic than upon the plain silver bromide 
plate. It appeared of interest to find if this loss of sensitiveness 
could be traced to a loss of activity of the Hosin sensitizer to 
rays of low refrangibility, thus accounting for the more marked 
effect upon the isochromatic plate. 
To investigate this point, I modified a quarter-plate printing 
frame, so that a plate might be divided into a hot and cold area 
