the Study of the Properties of Electrie Waves. 59 



key. The radiating apparatus may thus be made very small 

 and portable, and requires very little attention. After the 



Fig. 2.— The Radiating Box. 



storage cell is once charged, experiments may be carried on 

 for days, a flash of radiation being produced at any time by 

 merely manipulating the key. 



Spiral Spring Receiver. 



For a detector of radiation I used a form of Prof. Lodges 

 coherer. At first I used one made of metallic filings, origi- 

 nally discovered by M. Branly ; but great difficulty was 

 experienced in making the receiver respond to different 

 vibrations, and in the capriciousness of its response. The 

 difficulty was still further enhanced when the radiator and 

 .the receiver had to be enclosed in narrow tubes to enable 

 angular measurements to be made with any accuracy. It 

 seemed to me that the frequent loss of sensibility might be 

 due to the particles getting jammed together, and the fatigued 

 condition of contact surfaces. In order to avoid this I used 

 a layer of narrow spirals of steel, lying side by side, and 

 rolling on a smooth surface. The points of contact are 

 numerous, and fresh surfaces can be brought into action bv 

 a slight rolling of the spirals. By this spiral-spring arrange- 

 ment the pressure exerted on contiguous spirals is also made 

 fairly uniform. 



From a series of experiments carried out to determine the 

 other causes which may be instrumental in producing loss of 

 sensibility, I found that the sensibility of the receiver to a given 

 radiation depends (1) on the pressure to which the spirals are 

 subjected, and (2) on the E.M.F. acting in the circuit. The 

 pressure on the spirals may be adjusted, as will be described 

 later on, by means of a fine screw. The E.M.F. is varied by 



