296 DISCOVERY CH. 



those of violet light, produced by about seven hundred 

 millions of millions of vibrations in the ether per second. 

 This frequency of oscillation decreases as we pass down 

 the scale of colour through blue, green, yellow and orange 

 to red light, which is caused by about four hundred 

 millions of millions of etheric vibrations in a second. 

 Hertzian waves are due 'to much slower vibrations in 

 the ether a few millions per second and though they 

 do not affect our visual sense directly, they have precisely 

 the same other properties as waves of light. Light and 

 electricity are, in fact, merely different manifestations 

 of waves in a universal medium, the undulations in the 

 case of visible light being from about one thirty- 

 thousandth to one sixty-thousandth of an inch in length, 

 while the waves used in wireless telegraphy may be 

 from one foot to one thousand feet long, from crest to 

 crest. 



Soon after Hertz had described his remarkable 

 researches on the production and detection of electro- 

 magnetic waves, the scientific world realised their import- 

 ance. It was pointed out that as Hertzian waves possess 

 the property of passing through fog or material obstacles 

 they could be used for a system of wireless telegraphy. 

 Among the men of science who saw clearly the pos- 

 sibilities of the application of the waves for this purpose 

 was Sir William Crookes, who, writing on Hertz's 

 work in The Fortnightly Review of February, 1892, 

 said : 



Here is unfolded to us a new and astonishing world one 

 which it is hard to conceive should contain no possibilities of 

 transmitting and receiving intelligence. Rays of light will not 

 pierce through a wall, nor, as we know only too well, through a 

 London fog. But the electrical vibrations of a yard or more in 

 wave length will easily pierce such medium, which to them will 

 be transparent. Here, then, is revealed the bewildering possi- 



