WET AND DRY PLATES. 



213 



an ordinary paraffin lamp and bull's-eye condenser of 

 3 inches focus, the shortest exposures for good pictures 



FIG. 195. 



with Mawson and Swan's "15 times" sensitive plates have 

 been found as follows : 



Dr. Carl Setter, in a communication to the ' American 

 Journal of Microscopy' upon this subject, seems to prefer 

 wet plates to dry ones, and adduces arguments in support 

 of his views, one of which is cheapness. The cost of plates 

 by the wet or dry process is so small that this item need 

 not enter into the calculation ; moreover, dry plates are 

 rapid, so convenient, and with good manipulation give such 

 excellent results, that the author pleads for the use of them 

 exclusively in producing negatives. 



There are many kinds of dry plates to be met with in the 

 market, nearly all of which are now prepared from gelatine 



