93 



is gradually darkened towards either extremity until it be- 

 comes a deep black. 



I have not had many opportunities of experimenting with 

 the Catalysotype, but it certainly promises to repay the trou- 

 ble of further investigation. The simplicity of the process, 

 and the sensibility of the paper, will, no doubt, make it be 

 extensively used. It has all the beauty and quickness of the 

 Calotype without a tenth of its trouble, and very little of its 

 uncertainty ; and, if the more frequent use of it by me, as 

 compared with other processes, does not make me exaggerate 

 its facility of operation, I think it is likely to be practised 

 successfully by the most ordinary experimenters. 



SUPPLEMENT TO THE PRECEDING PAPER. 



P. S. — Since the preceding Paper was written I have 

 been experimenting with the Catalysotype, and one day hav- 

 ing had many failures, which was before quite unusual with 

 me, lam induced to mention the cause of them, for the benefit 

 of subsequent experimenters. The paper 1 used was very 

 stiff, and highly glazed, so that the solution first applied was 

 not easily imbibed. The blotting-paper was very dry and 

 bibulous. When using the latter, I removed nearly all the 

 solution of iron from the first, and, of course, did not obtain 

 the desired result. 



While varying the process in endeavouring to find out the 

 cause just mentioned, I discovered that the following propor- 

 tions gave very fine negative pictures, from which good posi- 

 tive ones were obtained : — take of syrup of ioduret of iron, dis- 

 tilled water, each two drachms; tincture of iodine, ten to twelve 

 drops : mix. First brush this over the paper, and after a 

 few minutes, having dried it with blotting-paper, wash it 

 over in the dark (before exposure in the camera) with the fol- 

 lowing solution, by means of a camel-hair pencil : — take of 

 nitrate of silver one drachm; pure water one ounce: mix. 

 This gives a darker picture than the original preparation, and, 

 consequently, one better adapted for obtaining positive ones ; 



