7 
greater part of 1689, as Member of the Convention Parlia- 
ment, when it is certain that this portrait was painted ; and 
he added, that he had not been able to discover any other 
portrait of him painted earlier than, or about, this interesting 
period of his life, nor any other, till several years later 
(probably twenty), when success had greatly changed his 
countenance. 
PHOTOGRAPHICAL SECTION. 
October 4th, 1866. 
Dr. J. P. Joule, F.R.S., &c., Vice-President of the Section, 
in the Chair. 
A paper was read On a Process for Printing Photographs 
in Various Colours,” by J. A. Gatty, Esq. 
My process is based upon the property possessed by ferri- 
cyanide of potassium, of forming clear solutions with certain 
metallic salts, producing insoluble compounds when the 
mixture is brought into contact with a deoxidising agent, 
the rays of the sun acting as such, a perfect precipitation 
takes place upon paper or other material prepared with the 
above-named solution. In producing the specimens sent 
herewith, I applied to the paper a concentrated solution, 
formed of equal parts of ferricyanide of potassium and nitrate 
of lead, having found the latter to answer very well, not only 
as a means of forming a precipitate, but also for assisting in 
the production of numerous colours. After drying the paper, 
it was exposed to the sun for about half an hour, and then 
washed in water in order to dissolve all the unaffected ferri- 
cyanide of potassium and nitrate of lead. I have noticed that 
the sun acts much quicker when there is a little moisture 
present. I have, therefore, placed a damp cloth between two 
or three thicknesses of paper behind the prepared paper. 
