[ 549 ] 

 LXYII. Intelligence and Miscellaneous Articles. 



ON A NEW DYNAMOMAGNETIC PHENOMENON. BY MM. TREVE 

 AND DURASSIER. 



T ET a horse-shoe magnet of any length be covered on one face 

 -*-^ with varnish, or, better, with a strip of glass. If a cylinder of 

 soft iron be placed upon its neutral part, the cylinder will begin to 

 move toward the poles, which it reaches in a time which is of 

 course a function of the weight of the cylinder and the coercive 

 force of the magnet. 



The magnetic attraction, therefore, is here exerted, not in the 

 limited field which has been recognized for it, but over the, whole 

 extent of the magnet. 



Hence results a new mode of valuing magnetic force, by the 

 mechanical work which it has performed. The product of the 

 weight of the iron moved, multiplied by the space passed through, 

 divided by the time elapsed, will be the precise measure of this 

 magnetic force. If, for example, the force be determined for three 

 large and three small magnets, identical in shape and weight, and 

 containing respectively 025, 0*5, and 1 per cent, of carbon, it will 

 perhaps be possible to define the unit of magnetic force ("the 

 magnety"), and fix its equivalence in kilogrammetres. 



We had made great efforts to determine the magnetic conduc- 

 tivity of steels in proportion to their content of carbon ; but the 

 want of a rigorous mode of valuation of magnetic forces had always 

 prevented us. The phenomenon above described will fill the gap 

 and permit us to accomplish this important purpose. We must 

 here, however, indicate the course we have followed. 



If, for instance, a steel with 1 per cent, carbon be taken, of our 

 first series of Creusot, it is known that its coercive force is ap- 

 proximately 47 degrees on the compass. 



Let us place it in an induction-coil, like an ordinary electro- 

 magnet, giving to the coil the proportions of length, section, wire,&c. 

 fixed by the formulas of M. du Moncel for the purpose of obtain- 

 ing a maximum of magnetic power, and send through it a strong 

 current in the wished-for direction. Under these conditions the 

 magnet gives no longer 47, but 64 degrees. If 47 and 64 were 

 absolute numbers, one could say that the magnet A l has 47 of 

 permanent magnetism, but can take 64 in the temporary state. 

 64 would represent the magnetic capacity of the magnet with 1 per 

 cent, carbon — that is to say, the maximum of magnetism which it is 

 capable of receiving. The difference between 64 and 47 would 

 give the magnetic conductivity. 



]S"ow let the extreme steel of the series be E, with 0*25 per cent. 

 of carbon. Its coercive force is 13. If to it be applied the same 

 coil as to A 1? since they are identical in form and weight, its magnetic 

 capacity is found to be 69. The difference between 69 and 13 

 would be the magnetic conductivity of the steel with 0*25 per cent, 

 of carbon. 



