OF ARTS AND SCIENCES. 275 



knocked nearly all the magnetism out of the ring, Tliis was then 

 detached from the galvanometer and magnetized as before, when it 

 again gave the same large deflection it gave at first. The same con- 

 ditions were tried with other rings, and in each case it was found that 

 a vigorous stroke upon the ring magnet had the same destroying effect 

 upon the magnetism as it is known to have upon magnets having es- 

 ternal fields. 



XV. The flexible ring was now put in circuit again, and vigor- 

 ously jerked with the hands. A very few such movements served to 

 destroy neai-ly all the magnetism present, requiring the remagnetiza- 

 tiou of the ring. 



As flexible iron rings such as I wanted were not easy to make, I 

 procured some steel wire rope of the right size, and the ends were 

 welded for me through the courtesy of Professor Elihu Thompson of 

 Lynn, by his electrical welding process. Such a ring about a foot 

 in diameter allows a movement of five or six inches to one of its sides. 

 This when wound with four or five hundred turns of No. 22 wire may 

 be magnetically saturated by sending a current through the wire, leav- 

 ing the ring charged. The terminals may now be connected with a 

 proper galvanometer, and changes in the form will discharge the ring. 



These experiments prove : — 



1. That a change in the form of a magnet causes a corresponding 

 change of stress in the field. 



2. That periodic changes in form due to elasticity of form, such as 

 are called sound vibrations, set up similar periodic changes or waves 

 in the magnetic field. 



3. That such sound vibrations of a magnet act upon other magnets 

 like sound vibrations, and set them into corresponding vibratory move- 

 ments, sympathetic or forced; sympathetic when the receiving magnet 

 has the same pitch as the transmitting magnet, and forced when it has 

 not the same pitch. 



4. That such sound vibrations in the receiving magnet cause a cor- 

 responding change of form in its magnetic field, which manifests itself 

 by electric currents in circuits surrounding it. 



Sir William Thomson has frequently said that he could understand 

 a mechanical idea when he could make a model of it, but could not 

 otherwise. If one assumes that the ultimate atoms of iron are mag- 

 nets, as is thought most probable now, — or holds, by Ampere's hypoth- 

 esis, that currents of electricity circulate about each atom, making it 



