CHAPTER IX. 

 ON THE SELECTION OF PLATES. 



THERE are not a few able photo-micrographers who assert 

 that the wet collodion process is superior to the gelatine 

 bromide process for photo-micrography. The writer is in- 

 clined to dispute this point, on the following grounds : The 

 strongest argument of the advocates of wet collodion is that 

 the deposited metal forming the image is in the wet process 

 in a finer state of division than it can be in any gelatine 

 process. The writer traverses this statement at the outset. 

 The wet collodion process gives a more finely grained image 

 than the rapid gelatine emulsion gives, certainly ; but a gela- 

 tine emulsion made with certain precautions, and suitably de- 

 veloped, yields a metallic image quite as fine in grain as a 

 wet collodion image, if not finer. But the gelatine emulsion 

 for this must be very " slow," such as that used for the pro- 

 duction of lantern slides in which the visible image approaches 

 a stain more than a deposit in appearance. Moreover, the de- 

 posit in the most sensitive plate is so fine as to be incapable of 

 producing the slightest granular effect by direct contact print- 

 ing, or even after enlargement of the negative by photographic 

 processes up to at least 4 diameters. And the writer is very 

 strongly of opinion, having worked and thought out the mat- 

 ter very carefully, that both in theory and in practice no ad- 

 vantage whatever is gained, or can be expected to be gained, 

 by " camera enlargement " of a negative, over a negative of 

 the desired amplification produced directly with the micro- 

 objective. If, for example, an ultimate magnification of 300 

 diameters is required, it will be better produced by direct am- 

 plification by an objective than by making a negative at 

 " X 100," and enlarging 3 diameters in the camera ; and an 

 enlargement of 3 diameters, if properly managed will not, 



