524 



KINETICS OF BIOLUMINESCENT REACTION. 



intensities of the incident light are plotted as abscissae, and the 

 resulting densities as ordinates. The term density is defined as the 

 logarithm of the opacity, while the opacity of a film or plate is itself 

 the reciprocal of the transmission. In the determination of photo- 

 graphic densities, therefore, it becomes necessary to secure a method 

 for measuring transmission values; that is, to determine what percent- 

 age of a given constant light is able to pass through the density in 

 question. Various methods for such studies have been perfected. 



3y6 



g.4 



t2 



QO 



0.8 



Log I 



Fig. 1. Curve of blackening. Straight line portion determined by points 

 obtained with the calibration method using Cypridina light itself as the light 

 source. Dotted lines indicate diagrammatically how the over-exposure (A) and 

 under-exposure (B) segments would appear. Abscissae represent logarithms 

 of light intensities (filter transmissions). Ordinates represent photographic 

 densities. 



Perhaps the most popular has been the polarization photometer of 

 Martens. In my own work I have employed the optical pyrometer, 

 a photometric instrument of great accuracy. 



The nature of the curve of blackening can be best understood by 

 reference to Fig. 1 , which will also indicate how closely it is possible 



