Mr M. Ponton 07i the Photographic Thermometer. 271 



the stem, in such a manner that the shadow of the empty part 

 of the bore is reduced almost to nothing, while that of the filled 

 portion is considerably expanded, and well defined. A little 

 practice sufiices to hit the best adjustment. 



The next point was to obtain a photographic paper suf- 

 ficiently sensitive to be afiected by artificial light at a conve- 

 nient distance, and in a sufficiently short time, but which could 

 at the same time be kept long enough without injury. After 

 various unsuccessful attempts, I have ascertained that paper 

 prepared in the manner to be described, answers the purpose 

 perfectly. The process is a modification of that discovered by 

 Hunt, and to which he has given the name of Energiatype. 



The paper is first to be coated with either the iodide or the 

 chloride of silver ;— 1 prefer the latter. The usual mode of 

 washing, first with the nitrate of silver, and then with either the 

 iodide of potassium, or the chloride of sodium, maybe adopted 

 for this purpose. It is desirable to have a good coating of 

 either the iodide or chloride of silver on the paper. The so- 

 luble salt having been well washed out, by immersing the paper 

 in clean cold water, it is next to have applied to it a saturated 

 solution of succinic acid. In this state the paper may be pre- 

 served for any length of time, if kept dry, and carefully ex- 

 cluded from light. 



Before use, a wash of the aceto-nitrate of silver, as directed 

 to be prepared by Talbot, is to be applied. This gives the 

 paper the necessary degree of sensitiveness, and in this state it 

 may be kept without injury to its properties for two or three 

 days, but not more. 



If the aceto-nitrate be applied without the previous wash of 

 succinic acid, the paper will be equally sensitive ; but it will 

 blacken spontaneously in the dark, and is therefore useless for 

 the purpose. The succinic acid thus appears to exert a con- 

 servative influence in preventing spontaneous decomposition. 



The photographic image formed on this paper is latent, and 

 requires to be brought out by the application of a saturated 

 solution of the sulphate of iron, mixed with three or four times 

 its bulk of mucilage of gum-arabic. This mixture should be 

 freshly prepared, for it soon becomes a jelly, which is unfit for 



