large and very small' Alternating Currents. 



275 



similar method the ratio of current transformation 'may some- 

 times be increased. The connexions in this case are shown 



in iig. 2. 



Fig. 2. 



AMPERES 



Transformers with Iron Cores. 



I have recently investigated the case of transformers with 

 iron cores whose secondary circuits were made highly induc- 

 tive. This was done by short-circuiting the secondary in each 

 case through a Kelvin 100-ampere balance. 



Two transformers were thus tested-^an iron-ring trans- 

 former with very small magnetic leakage, and a small trans- 

 former with open iron circuit. The first of these had a 

 primary of 764 turns of No. 16 S.W.G. wire, and over this a 

 secondary of 48 turns of 7/16 wire. The core of the second 

 was a short bundle of iron wires, over which were wound the 

 primary of 38 turns of No. 16 S.W.Gr. wire, and over it a 

 secondary of about 3000 turns of No. 26 S.W.G. 



The ring transformer was first tested with a Kelvin 10- 

 ampere balance as secondary load, the frequency being 84 ~ 

 per second. The balance had a resistance of about 0*55 ohm 

 and an inductance of about 0*0016 henry. The results given 

 in Table II. show that with this amount of resistance in the 



secondary the -J- is by no means constant. 



X2 



