CHAPTER XX. 



SOME CURIOSITIES. 



Until within recent years it was never sup- 

 posed that a sunbeam would ever laugh except 

 in poetry. But the modern scientist has taken 

 it out of the realm of poetry and put it into the 

 prosy play of every-day life. The Radiophone, 

 invented by A. G. Bell, is an instrument by 

 which articulate or other sounds are transmit- 

 ted through the medium of a ray of light. It 

 has as yet no practical application and has 

 never gone beyond the experimental stage, but 

 as a bit of scientific information it is very in- 

 teresting. 



If we introduce into an electric circuit a 

 piece of selenium, prepared in a certain way, 

 Distance as an electric conductor under- 

 goes a radical change when a beam of sunlight 

 is tin-own upon it. For instance, a selenium 

 ci-H. <(. called, that in the dark would measure 

 hms resistance, would have only about 

 150 ohms when rxj >"-<<] to sunlight. This 

 amount of variation in a short circuit of low 

 resistance would produce a considerable change 

 171 



