114 



to be tested. If the insulation was good 

 on that particular circuit, the tube 

 showed a bluish light, which was ob- 

 served through the eye-hole. If it was 

 faulty, this static effect did not take 

 place; the tube remained dark, and the 

 attendant knew that the particular main 

 was faulty, and must be repaired. If 

 complicated tests were used, requiring 

 elaborate apparatus which could not be 

 easily carried about, the men would be 

 sure to neglect it. With a little instru- 

 ment like that exhibited, two or three 

 circuits could be tested in half a minute. 

 The author also exhibited an armature- 

 coil of one of Mr. Mordey's dynamos 

 shown in Fig. 15 ; also various measur- 

 ing instruments, a safety apparatus in- 

 vented by Captain Cardew, and various 

 photographs of the large dynamos made 

 by Mr. Ferranti. 



Mr. W. H. Preece said that it might 

 not be out of place if he were to give a 

 brief account of the steps, taken in re- 

 cent years, to solve the very difficult 

 question of the economical distribution 



