166 RESPONSE IN THE LIVING AND NON-LIVING 



decline. Sometimes this process is very rapid, and 

 in any case, under continued light, the deflection falls. 



(1) The decline may nearly reach zero. If now the 

 light be cut off there is a rebound towards recovery 

 downwards, which carries it below zero, followed by an 

 after-oscillation (fig. 108, a). 



(2) If the light be continued for a longer time, the 

 decline goes on even below zero ; that is to say, the 



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FIG. 108 DECLINE UNDER THE CONTINUED ACTION OF LIGHT 



(a) Decline short of zero ; on stoppage of light, rebound downwards to zero ; 

 after-oscillation. 



(6) Decline below zero ; on stoppage of light, rebound towards zero, with pre- 

 liminary negative twitch. 



(c) The same, decline further down ; negative twitch almost disappearing. 



response now becomes apparently negative. If, now, 

 the light be stopped, there is a rebound upwards to 

 recovery, with, generally speaking, a slight preliminary 

 twitch downwards (fig. 108, 6, c). This rebound 

 carries it back, not only to the zero position, but some- 

 times beyond that position. We have here a parallel to 

 the following observation of Dewar and McKendrick : 



