ELECTRIC AND HEAT WAVES NICHOLS AND TEAR 



181 



walled brass case C and B. From the inner case, C, the air can be 

 exhausted through the tube T. This case has two window openings, 

 one covered by the quartz plate, Q, admitting the electric waves, 

 and the other, O, through which the rotation of the suspension can 

 be measured, covered by glass. The outer protecting case, B, has 

 corresponding openings, and the beam of the electric waves is 

 focused on the vanes, V t and V 2 , of the suspension by the paraffin 

 lens L. The forces due to the resistance heatine: of the electric 



8 lb 24 32 40 48 Si, 

 PATH DIFFERENCE. (IKM) 



Fig. 3. — Interference curves taken with the Boltzmann mirrors 



waves which rotate the suspension are opposed by the resulting twist 

 of the quartz fiber F. The angle of twist of the fiber under proper 

 conditions is found to be proportional to the intensity of the electric 

 wave radiation, and thus quantitative measurements of wave in- 

 tensity are easily made. 



Wave-length measurements. — Wave-length measurements of the 

 radiation received from the electric oscillator were made with two 

 types of analyzers. The first, shown in Plate 2, Figure 1, is the in- 

 terferometer, due to Boltzmann, consisting of two parallel mirrors, 

 M x and M 2 , of which M x can be displaced backward or forward with- 



1454—25 13 



