INORGANIC RESPONSE 



i63 



effect attains a maximum at which it remains constant 

 for some time. If the exposure be maintained after 

 this for a longer period, there will be a decline, as 

 we found to be. the case in other instances of continued 

 stimulation. The appearance of this decline, and its 

 rapidity, depends on the particular condition of the 

 substance. 



When the sensitive element is considerably strained 

 by the action of light, and if that light be now cut 



FIG. 105. AFTER-OSCILLATION 



Exposure of one minute followed by obscurity of one minute. Note the decline 

 during illumination, and after-oscillation in darkness. 



off, there is a rebound towards recovery and a sub- 

 sequent after-oscillation. That is to say, the curve of 

 recovery falls below the zero point, and then slowly 

 oscillates back to the position of equilibrium. We 

 have already seen an instance of this in fig. 102. Above 

 is given a series of records showing the appearance 

 of decline, from too long-continued exposure and re- 

 covery, followed by after-oscillation on the cessation 

 of light (fig. 105). Certain visual analogues to this 

 phenomenon will be noticed later. 



M 2 



