1901.] on the Response of Inorganic Matter to Stimulus. 633 



Perhaps before completing what I have to say on 

 Stimulus the modification of response by external agencies, 



of Light. it will be well to make some reference to the ac- 



tion of other forms of stimulus and other modes 

 of detection of response. In this investigation I have used the 

 mechanical form of stimulus as being the simplest and giving rise 

 to the fewest complications. Time does not allow of my entering 

 here upon the question of the action of electric stimulus in causing 

 response. I have dealt with this subject in some detail elsewhere. 

 I may, however, say a few words on the effect of light stimulus. 



If one of the sensitised wires in the cell already described be 

 subjected to light it will give an electric response, and under certain 

 circumstances an oscillatory after-effect will be seen on the cessation 

 of light. This latter fact may, perhaps, explain certain phenomena 

 of visual recurrence to be noticed presently. 



The molecular strain produced by stimulus can 

 Artificial not only be detected by the phenomena of electro- 



Betina. motive variation, but also by conductivity varia- 



tion.* Acting on this principle, I have been able 

 to construct an artificial retina. The sensitive receiver is contained 

 inside a hollow spherical case, provided with a circular opening in 

 front, in which a glass lens is placed, corresponding to the crystalline 

 lens. You now see before you a complete model of an artificial eye.j 

 When this is interposed in an electric circuit, with a sensitive galva- 

 nometer as indicator, you observe the response to a flash of light by 

 the galvanometer deflection. I throw red, yellow, green and violet 

 lights upon it in succession, and you see how it responds to all. Note 

 how strong is the action of yellow light, the response to violet being 

 relatively feeble. Indeed, the most striking peculiarity of this eye 

 is that it can see lights not only some way beyond the violet, but 

 also in regions far below the infra-red, in the invisible regions of 

 electric radiation. It is in fact a Tejometer (Sanskrit tej = radiation), 

 or universal radiometer. 



Observe how each flash of invisible light I am producing with 

 this electric radiation apparatus, calls forth an immediate response, 

 and how the eye automatically recovers without external aid. This 

 will show the possibility of an automatic receiver which will record 

 Hertzian wave-messages without the intervention of the crude tap- 

 ping device. 



This retina has, as will be seen with regard to spectral vision, an 

 enormous range, extending far beyond the visual limits. We can, 

 however, reduce its powers to a merely human level by furnishing it 



* See ' On the Similarity of Effect of Electrical Stimulus on Inorganic and 

 Living Substances.' — Electrician, Sept. 1900. 



f I hope to publish a complete account of this instrument at a future date. 

 The descriptions which follow are more detailed than time permitted on the 

 10th of May. 



