226 



HEXRY A. BOWL AND 



tage, since each coil acts very nearly the same as every other in produc- 

 ing force. But if the core is very short indeed, wire must be piled on 

 it to a very great extent in order to get sufficient magneto-motive force, 

 and as iron is cheaper than copper it might he better to lengthen out 

 the core. I do not know where the lengthening should end, but I 

 should suppose when the requisite wire on the magnet makes a moder- 

 ately thin layer. Of course, as we lengthen out the magnet, the resist- 

 ance of the circuit to magnetization becomes greater; but that is a very 

 small quantity. I do not suppose the increase is very much for a 

 considerable lengthening of the magnet. As I said before, the magnetic 

 conductivity of iron is many times greater than that of air, and we can 

 lengthen out the cores without producing much loss on account of that 

 lengthening. 



Some persons have suggested that there might be a slight gain from 



FIG. 7. 



the fact that iron, after it has been magnetized a great number of times 

 in the same direction, rather likes to be magnetized in the same direc- 

 tion afterwards. If the core is made of any material similar to steel, 

 such as wrought iron or anj'thing of that sort, it might be possible to 

 have some gain from the coercive power of the magnet. There would 

 be loss from that cause at first; but from the continual use of the 

 machine I think it very likely the iron might get a set in the direction 

 of the force. If the core were of steel, for instance, it might be that 

 one could send a strong current through at first and magnetize the steel, 

 and then be able to diminish the current considerably and still keep up 

 a very large magneto-motive force. I do not know how practical that 

 would be, but it seems to me that one could produce a very strong field 

 in that way. In the commencement of the operation of the machine, 

 we would have to send a powerful current to magnetize the steel, and 

 then, without stopping the current, to diminish it. Then the set of 



