62 



L. N. M. DUYSENS 



scattering by the cells and the best time resolution. However, second- 

 order effects on the compensation owing to scattered or fluorescent 

 hght must be eliminated. This may be done (a) by minimizing the 

 scattered and fluorescent Hght by means of filters, (6) by using two 

 sectoriated rotating disks, one in front of the phototube to cut off the 

 hght while the exciting hght is being admitted through a hole in the 

 other disk. 



MIRRORS 



HOLES 



PROJECTION 

 LAMP 



Q 



t 



COMPENSATING 

 m BEAM 



\. "^^A^ SUSPENSION f 



MONOCHROMATOR 



RECORDER 



AMPLIFIER 

 AND PHASE 

 SENSITIVE 

 RECTIFIER 



MULTIPLIER 



Fig. 1. Diagram of apparatus for measuring changes in absorption spectrum of a 

 suspension of photosynthesizing cells. 



Apparatus for measuring transients. Fast changes may be measured 

 by means of a photomultiplier connected to an oscilloscope. If a 

 measurement is completed in a short time, slow changes in intensity 

 of the hght sources, in multiplier, and in sensitivity of oscillograph 

 amplifier may be neghgible. The contmuous current caused by the 

 measuring beam may be eliminated by means of a condenser coupling 

 or by cancehng it out by a constant countercurrent. 



Witt (6) succeeded in measuring in this way rapid changes in ab- 

 sorption brought about by hght flashes. (So far, no description of his 



