184 
last few days, since hearing of Daguerre’s secret, and also that Fox 
Talbot has got something of the same kind.” [Here follow 
some trials of the relative sensitiveness of the nitrate, carbonate, 
acetate, and muriate of silver. I should observe that at that time 
I did not even know what kind of pictures Daguerre had pro- 
duced. This process was not revealed till August, 1839.] 
“Exp. 1013. — Daguerre’s process — attempt to imitate. Requi- 
sites — 1st very susceptible paper — 2nd very perfect camera — 3rd 
means of arresting further action. Tried hyposulphite of soda to 
arrest the action of light by washing away all the chloride of silver 
or other silvering salt — succeeds perfectly. Papers half acted on, 
half guarded from the light by covering with pasteboard, were 
withdrawn from sunshine, sponged over with hyposulphite, then 
washed in pure water, dried, and again exposed. The darkened 
half remained dark, the white half white, after any exposure, as if 
they had been painted with sepia.” 
“Jan. 30, 1839. — Formed image of telescope with the aplanatic 
lens .... and placed in focus paper with carbonate of silver. An 
image was formed in white on a sepia colored ground .... which 
bore washing with hyposulphite of soda, and was then no longer 
alterable by light. Thus Daguerre’s problem is so far solved,” 
<kc. &c. 
“ Exp. 1014. — Jan. 30. Tried transfer of print and copper 
plate engraved letters,” Ac. &c. 
The publication of Daguerre’s process (according to Dr. Monck- 
hoven, for I cannot refer at present to the original document) 
took place on the 19th August, 1839. My early experiments 
printed in the notices of the proceedings of the Royal Society of 
March 14, 1839, in which occurs this passage in the abstract of a 
paper read to the Society : — 
“ Confining his attention in the present notice to the employ- 
ment of chloride of silver, the author enquires into the method by 
which the blackened traces can be preserved, which may be 
effected, ho observes, by the application of any liquid capable of 
dissolving and washing off the unchanged chloride, but leaving 
the reduced oxide of silver untouched. These conditions are best 
fulfilled by the liquid hyposulphites.” 
