176 On a new Photo-IAthographic Process. 



graphy, when the sensitive surface which is to receive the 

 impress of light in the first instance, and afterwards to 

 retain the greasy ink forming the picture, is spread upon 

 the stone itself. In explanation of my reasons for making 

 this examination, I may state that, as far as I can learn, all 

 the efforts which have been made to produce lithographs by 

 photographic means have been expended directly upon the 

 stone itself, and not, as in my own'process, upon a chemically 

 prepared transfer paper. 



Firstly, Exposure in the Camera. 



The exposure of the lithographic stones in the Camera is 

 a very difficult matter, owing to their varying dimensions, 

 their weight and bulk, and the serious difficulty which the 

 endeavour to make the surface of the stone coincide, as 

 regards position, with that of the ground glass side of the 

 camera, gives rise to. As long as we adhere to this method 

 of exposure, the cumbersome nature of the stones excludes 

 the application of photo -lithography to the reproduction of 

 landscapes altogether. It will also be seen that a sensitive 

 surface being exposed in this way must subsequently take 

 the ink upon the parts which have not been acted upon by 

 light; in other words, upon those parts of the stone cor- 

 responding to the unaltered portions of the said " surface." 



Secondly, Exposure under a Negative. 



This is the most obvious, and the most convenient means of 

 attaining the end we have in view ; but if we work with a 

 "sensitive surface" upon the stone itself, there are several 

 difficulties which present themselves. A negative, to possess 

 the sharpness from which good results may be obtained, 

 must be made upon glass, either by the collodion or albumen 

 process ; such a negative is, when taken in the usual way, a 

 " reversed negative ;" this when placed upon the stone, will 

 give a "direct positive" photographic delineation, and a 

 stone so prepared will give in the press " reverse positive" 

 prints; that is, prints of a nature utterly useless, except 

 perhaps in the case of portraits. To overcome this difficulty 

 either the collodion film must be taken off the glass and 

 turned upon the stone, or the glass with the sensitive film 

 upon it must be turned in the camera, when making the 

 negative, and the rays of light allowed to shine through the 

 glass plate, striking the sensitive film on its inner surface; 

 the inconvenience which both these alternatives occasion is 

 very great, and very apparent ; they are however, both per- 

 fectly feasible, although deficient in certain minor particulars 



