322 PROCEEDINGS OF THE AMERICAN ACADEMY 



XVII. 



CONTRIBUTIONS FROM THE PHYSICAL LABORATORY OF 

 HARVARD UNIVERSITY. 



A PAPER ON THE PROPAGATION OF MAGNETIC 

 WAVES IN SOFT IRON. 



By Harold Whiting. 



Presented by Prof. Trowbridge, Peb 14, 1881. 



When a rapidly alternating current is made to pass tlirough a coil 

 of insulated wire wound about one end of a bar of soft iron, the lat- 

 ter becomes the seat of a series of magnetic waves, whose velocity 

 and manner of propagation have, I think, not been determined. 



The object of the present paper is to show that these waves differ 

 in form, phase, and magnitude from the values assigned to them by 

 any possible theory of instantaneous propagation ; and that this rate 

 of propagation, as determined by actual observation, is not generally 

 very great, being measured in ordinary experiments by only a few 

 feet, or at most a few hundred feet per second : but that no fixed 

 velocity of propagation can be said to exist ; since it depends largely 

 upon the period of the wave, the material, dimensions, and accidental 

 conditions of the bar, the distance from the magnetizing coil, and. 

 even, in extreme cases, upon the strength and distribution of the 

 magnetic field. 



In developing the complex laws which determine the velocity of 

 propagation under so many variable conditions, I shall try also to 

 show that the close analogy between magnetism, electricity, and heat, 

 may be traced throughout the phenomena of magnetism in motion. 



As early as the spring of 1876 I had completed, under the direc- 

 tion of Professor Trowbridge, a series of measurements supplemen- 

 tary to those of Mr. Rowland, showing the distribution of magnetism 

 over a soft iron bar applied at one end to the pole of a permanent 

 magnet. The subject next assigned to me was naturally the rate of 

 this distribution, and of the propagation of magnetism in general. 



