yohn L. Baird 17 



100,000 signals per second, and it was at once realized that this 

 problem was on quite a different plane to the ordinary wireless 

 problem, such as sending signals by dots and dashes. 



By the aid of selenium pictures were reproduced by 

 telegraphy in 1907, when a picture of King Edward VII 

 was transmitted in twenty minutes by a German named 

 Korn. Since that date the sending of pictures by tele- 

 graphy has made rapid strides, and illustrations trans- 

 mitted over great distances in this way appear regularly 

 in our newspapers. But these later developments, even 

 had the results been available, would not have helped 

 those who in the closing years of the last century 

 sought the key to television, because with a picture it was 

 not necessary to transmit and receive the whole produc- 

 tion in a fraction of a second, whereas if television was to 

 be successful some method of sending nearly 100,000 

 signals per second must be discovered. 



More valuable was Hertz's discovery, in 1888, of wire- 

 less waves which made broadcasting possible. Another 

 step had been taken toward seeing at a distance, but still 

 both the possibilities of the invention and the method 

 were undiscovered. 



The Hertzian waves and the discovery of photo-electric 

 cells made it possible to transmit scenes infinitely faster 

 than had been possible by selenium, but here another 

 difficulty arose. The photo-electric cells were not suffi- 

 ciently sensitive, and would not respond to the small light 

 available. Shadows only were received — there was no 

 known method of amplifying the impulses sent out. 

 Thus it was found that if a human face were brilliantly 

 illumined by powerful lamps, the reflected light caught 

 and transmitted was less than one candle-power. 



For some years there was no further advance, until 

 developments in wireless, especially Sir John Fleming's 

 invention of the thermionic valve, encouraged the 

 pioneers of television to redouble their efforts, for the 



