AUTOMATIC RECORDER 



23 



on the diurnal variation of photosynthesis, the experiment 

 has to be continued for about ten hours. We have thus to 

 make provision for records of either short or long duration. 

 For immediate detection of the effect of physiological 

 variation it is desirable that the drum should revolve at a 

 quick speed. The distance between the two successive dots 

 representing the period of bubbling is then comparatively 



Fig. 3. The Automatic Recorder for Photosynthesis 



s, bubbler with stop-cock ; e, the electric pencil for completing 

 electric contact through drop of mercury, m ; a, adjusting 

 screw; v, voltaic cell; c, condenser; d, revolving drum; 

 w, electromagnetic writer ; G, governor, shown separately at 

 p with pair of hinged levers, h ; 1, ink-recorder. 



large, and any induced change in the rate of bubbling is 

 strikingly manifested by the shortening or lengthening of the 

 distance between the successive dots. For long-continued 

 experiments, on the other hand, the speed of the drum has 

 to be correspondingly reduced. The drums ordinarily 

 employed have the following drawbacks : 



(1) Each particular drum has a speed of revolution 

 which can only be varied within narrow limits. A number 



