114 MESSRS. J. HOPKINSON AND E. WILSON ON THE 
The ergs dissipated per cycle per cub. centim. are 26,000 by induced currents, and 
about 17,000 by magnetic hysteresis. This shows that according to good practice, 
where the wires in armature cores are of an order of 1 or 2 millims. diameter, the loss 
by induced currents would be but small as compared with the loss by magnetic 
hysteresis. This, of course, assumes the wires to be perfectly insulated from one 
another, which is not always realised in practice. 
Both the armature cores of dynamos and the cores of transformers are now usually 
made of plates instead of wire; roughly speaking a plate in regard to induced 
currents in its substance is comparable to a wire of a diameter double the thickness 
of the plate. We infer that the ordinary practice of making transformer plates 
about 4 millim. thick, and plates of armature cores 1 millim. thick, is not far wrong. 
Not much is lost by local currents in the iron, and the plates could not be much 
thicker without loss.* 



TABLE I, 
Ae rere era Maxinium force in Maximum induction | 
a gs paler ab = C.G.S. units. per sq. centim. 
magnetizing coils. H R 
d 
Fig. 10 sea a 0745 ioe 
Pris! ki ee ei eas 138 3:0 
2 eRableme ine 24, 4:96 | 8,000 
49 101 12,820 
Sy SS Mas ee ills | 774 16:0 14,495 
BS PORTALS) 1:80 37:2 | 15,480 
| 2°31 47-6 | | 
65 1345 | 




* The question of dissipation of energy by local currents in iron has been discussed by Professors 
J.J, Tuomson and Ewr1ns. See the ‘ Electrician,’ April 8th and 15th, 1892. 
