174 RESPONSE IN THE LIVING AND NON-LIVING 



If there has been a feeble initial current, this 

 oscillatory after-current, by algebraical summation, will 

 cause the current in the circuit to be alternately weaker 

 and stronger than the initial current. 



Visual recurrence, Translated into the visual circuit, 

 this would mean an alternating series of after-images. 

 On the cessation of light of strong intensity and long 

 duration, the immediate effect would be a negative re- 

 bound, unlike the positive after-effect which followed 

 on a short exposure. 



The next rebound is positive, giving rise to a sen- 

 sation of brightness. This will go on in a recurrent 

 series. 



If we look for some time at a very bright object, 

 preferably with one eye, on closing the eye there is 

 an immediate dark sensation followed by a sensation 

 of light. These go on alternating and give rise to 

 the phenomena of recurrent vision. With the eyes 

 closed, the positive or luminous phases are the more 

 prominent. 



This phenomenon may be observed in a somewhat 

 different manner. After staring at a bright light we 

 may look towards a well-lighted wall. The dark phases 

 will now become the more noticeable. 



If, however, we look towards a dimly lighted 

 wall, both the dark and bright phases will be noticed 

 alternately. 



The negative effect is usually explained as due to 

 fatigue. That . position of the retina affected by light 

 is supposed to be ' tired,' and a negative image to be 

 formed in consequence of exhaustion. By this exhaus- 



