OF AETS AND SCIENCES. 201 



If the heating is due to molecular movements produced by magnet- 

 izing and demagnetizing, — and tiie musical note is adduced as an evi- 

 dence of this, — the bar would vibrate as a whole, and would become 

 heated throughout on account of this vibration. It is difficult to con- 

 ceive how the surface action of magnetism can communicate vibra- 

 tions to a solid bar of iron one inch and a half in diameter. If the 

 bar vibrates as a whole, a certain amount of heating of the bar takes 

 place throughout its interior. Tlie heat in the interior of the bar, 

 however, must be less than that at the exterior, where the magnetiza- 

 tion exists in full strength. We believe, however, that the musical 

 note is due to a forced vibration in the coil of the electro-magnet, — 

 possibly due to electro-magnetic attractions ; for the note can be 

 heard when the iron core is removed, and is stronger when the core is 

 in place simply because the magnetic field is strengthened. 



The appearance presented by iron filings strewn upon the pole of a 

 straight electro-magnet, which is submitted to the action of an alter- 

 nating current, shows very strikingly the fact that it takes time to 

 magnetize, and that magnetism resides upon the exterior of electro- 

 magnets. Under the influence of strong currents alternating six thou- 

 sand times a minute, the electro-magnet is still capable of attracting 

 an armature with great force. The filings arrange themselves as 

 a narrow fringe or ring upon the circumference of the end of the 

 cylindrical bar constituting the core of the electro-magnet, leaving the 

 surface of the end of the cylinder entirely free from filings. If filings 

 are scattered upon this free portion of the surface, they waltz to the 

 circumference. The fringe of iron filings vibrates in unison with the 

 alternating currents. 



In connection with this investigation, it may be interesting to refer 

 to some experiments made by Lt.-Comm. A. G. Caldwell, U. S. N., 

 and ourselves, on demagnetization. These experiments were made in 

 1880, but have not been published. 



Perfect demagnetization, or entire absence of magnetism in a mass 

 capable of magnetism, is a condition of great rarity. Approximate 

 demagnetization has been brought about with some difficulty, but deli- 

 cate tests would show traces of polarity. 



We have, however, discovered a method by which complete de- 

 magnetization may be rapidly and easily produced. The principle 

 involved is the setting up of a state of powerful magnetic vibration, 

 by which all previous magnetic conditions are obliterated, and on the 

 subsidence of which no polarity remains. This state of vibration is 

 induced by an alternating current of sufficient strenyf.h. By this an 



