CHAPTER V 



DESCRIPTION OF THE APPARATUS 



Summary. — Construction of the apparatus — Slide, object-glass, ciroular 

 diaphragms — Erection of the dark background at the physiological 

 station — Dark background for photographing objects in water — 

 Photography of light objects in darkness or in a red tight — Colour 

 of objects, and way of illuminating them — Disposition and pre- 

 paration of the dark field — Choice of the object-glass — Focussing 

 — How to take the photographs. 



Chronophotographic Apparatus. — An ordinary photo- 

 graphic camera can be used in chronophotography, 

 provided that it is furnished with a diaphragm which 

 gives very short periods of exposure at regular in- 

 tervals of time. For this purpose the simplest arrange- 

 ment, and the one we originally employed, is a disc 

 which is provided with small foramina, and which 

 revolves in a slot cut in the mounting of the objective. 

 The disc is made to revolve by a system of pulleys 

 and a continuous chain worked by clockwork and 

 controlled by a good regulator. But there is a diffi- 

 culty in combining a clockwork motor and a photo- 

 graphic camera, as well as in changing the disc 

 from time to time, as the rate and frequency of the 

 exposures may require, and this has induced us to 

 abandon so clumsy an apparatus. We determined to 

 construct a special instrument at once portable and 

 capable of being regulated as desired. Such an ar- 

 rangement is the more necessary because there are 



