THE 
LONDON, EDINBURGH, ann DUBLIN 
PHILOSOPHICAL MAGAZINE 
AND 
JOURNAL OF SCIENCE. 
[FIFTH SERIES.] 
AP Rk FL 1885, 
XXIX. Contributions to the Theory of Magnetism. 
By WERNER SIEMENS*. 
SINCE the efficient construction of electromagnetic ma- 
chines has acquired great practical importance, the 
question has arisen in very various forms, how to choose the 
form and mass of the magnets so as to obtain the greatest 
efficiency with the smallest expenditure of material and space. 
The ingenious theories which have been proposed as the result 
of the greatest skill and mathematical knowledge seldom give 
the required indications for the solution of these problems. 
The reason of this is, no doubt, that the production and distri- 
bution of magnetism in magnetic bodies, of which practically 
only iror in its various molecular conditions is in question, 
the action at a distance of the magnetism present, and the 
consequent strength of the magnetic field, and, lastly, the 
reciprocal action of the latter upon the strength of the mag- 
netism produced in the iron and its distribution, have, as a 
rule, been separately considered and submitted to calculation. 
EKyen if we obtain thus the fundamental data for the solution 
of the numerous problems proposed, yet the practical man is 
bewildered by a number of laws and empirical formule, which 
make it impossible for him to obtain a clear conception of the 
causal connection of phenomena which may serve him as a 
guide in his designs. ‘This unsatisfactory condition may 
result from the fact that all magnetic theories started from 
permanent magnetism, in the same way as electric theories 
* Translated from Wiedemann’s Annalen, vol. xxiy. No.1, p. 98 (1885). 
Phil. Mag. 8. 5. Vol. 19. No. 119. April 1885. S 
