Sir John Robison on Daguerre's Photography . 155 



beauty, and they may be exposed to continued sunshine with- 

 out undergoing the slightest alteration. 



I have succeeded also in taking impressions with the chlo- 

 ride in the same way — but it is necessary, for the success of the 

 process, to use the solution of the iodide much weaker than for 

 the phosphate, because the chloride is more easily acted on. 

 In both cases it ought to be made of- such strength that it just 

 acts, and then, before using it, it must be weakened by the ad- 

 dition of a little water. For the phosphate, it will be found, 

 in general, that 1 of salt to 10 of water, and for the chloride, 

 that about 30 of water, will give a solution of the requisite 

 strength. Of course, in preserving the specimens, the precau- 

 tions as to washing and pressure must be attended to. 



Notes on Daguerre's Photography. By Sir John Robison, 

 Secretary to Royal Society of Edinburgh, &c. &c. (Com- 

 municated by the Society of Arts). 



Sir — Tn compliance with the request that I should commit to 

 writing and put into your hands the substance of what I com- 

 municated to the Society of Arts in reply to the questions put 

 to me at the last meeting, I beg to state, that circumstances 

 having led to my being included in a small party of English 

 gentlemen who were lately invited to visit the studio of M. 

 Daguerre, to see the results of his discovery, I had an op- 

 portmiity of satisfying myself, that the pictures produced 

 by his process have no resemblance to any thing which, as 

 far as I know, has yet been produced in this country ; and 

 that, excepting in the absence of colour, they are as perfect 

 images of the objects they represent, as are those which are 

 seen by reflection from a highly polished surface. The per- 

 fection and fidelity of the pictures are such, that, on exa- 

 mining them by microscopic power, details ai'e discovered 

 which are not perceivable to the naked eye in the original ob- 

 jects, but which, when searched for there by the aid of optical 

 instruments, are found in perfect accordance : a crack in plas- 

 ter, a withered leaf lying on a projecting cornice, or an accu- 



