30 CHAP. IV. AUTOMATIC RECORD OF EVOLUTION OF OXYGEN 



The accuracy of the results thus obtained is of a high 

 order, as will be found in the various determinations given 

 in the following chapters. 



Summary 



The record of successive bubbles of oxygen is ob- 

 tained by an electric device which actuates the Electro- 

 magnetic Writer to inscribe successive dots on a revolving 

 drum, the speed of which may be adjusted within wide 

 limits. 



The advantages secured by the new method are : 

 (i) Numerous corrections are rendered unnecessary, 

 since the external conditions are maintained constant 

 during the relatively short period of the experiment. 



(2) Being automatic, all personal errors are eliminated. 



(3) Shortening the period of the experiment also 

 eliminates the effect of physiological depression brought on 

 by prolonged stimulation under light. 



(4) Finally, the photosynthetic activity is measured 

 directly from the rate of evolution of oxygen, thus dis- 

 carding the lengthy and laborious process of chemical 

 analysis. 



