j 



igo MARVELS OF FISH LIFE 



Working with an arc lamp of 1,200 candle-power, 

 and with a cooling tank between the light and the 

 object to be photographed, the usual exposure up to 

 twenty-five magnifications on a slow plate is one -fifth 

 of a second. Magnification above this requires one to 

 three seconds. The photograph of oyster spat on the 

 plate facing p. 148 shows a micro-photograph of the 

 living moving oyster spat magnified sixty times, and 

 taken at one-tenth of a second. When it is desired to 

 take a photograph from life size up to ten magnifica- 

 tions, the microscope is slipped out, and a tank is fixed 

 in place of the former, as illustrated. All the photo- 

 graphs, such as the embryo thornback ray, the hatching 

 salmon, and the developing roach, were taken in this 

 manner. 



The reason for the great length of bellows is that it 

 is possible to get considerable magnifications with lenses 

 of comparatively long focal lengths ; in this way objects 

 that have considerable thickness are sharp in focus all over. 

 It is not within the province of a book of this character 

 to deal at length with the various ways of manipulating 

 artificial light, or to describe the various modifications 

 of live cells that I use, but I would briefly refer to a 

 method I employ of obtaining a true rendering of trans- 

 parency in marine larvse and crustaceans. Take, for 

 example, a small crustacean. If the light is merely 

 transmitted through this animal into the lens, the 

 result obtained in no way suggests the transparency 

 of ths creature. (See top photograph in the opposite 



