THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



SEPTEMBER 1873. 



XX. On the Effects of Magnetization in changing the Dimen- 

 sions of Iron and Steel bars, and in increasing the Interior Ca- 

 pacity of Hollow Iron Cylinders. By Alfred M. Mayer, 

 Ph.D., Professor of Physics in the Stevens Institute of Techno- 

 logy, Hoboken, New Jersey, U.S.A. 



[Continued from vol. xlv. p. 359.] 



Part II. On the Elongations and Retractions of Rods of Iron and 

 Steel on their Magnetization and Demagnetization. 



TO study and measure with precision the minute elonga- 

 tions and retractions which rods of iron and steel un- 

 dergo on their magnetization and demagnetization, it is neces- 

 sary that the motions of the part of the measuring-apparatus 

 which records these changes in length should not be in the 

 least affected by outside vibrations transmitted to the appa- 

 ratus, but should be controlled alone by the molecular motions 

 in the rods which take place on changes in their magnetic con- 

 dition ; also the motions of this indicating part of the apparatus 

 should be synchronous with the motions in the rods, so that we 

 may be able to study the character as well as the amount of 

 these elongations and retractions. 



Several instruments have been devised by me which fulfil these 

 essential conditions ; but they were all abandoned (except one, to 

 be described in detail in Part IV. of this memoir) and preference 

 given to "the reflecting comparator and pyrometer" of our 

 esteemed colleague Mr. Joseph Saxton. This simple and precise 

 instrument is well known to American physicists as the apparatus 

 which has greatly aided in giving to the geodetic work of our 



Phil. Mag. S. 4. Vol. 46. No. 305. Sept. 1873. 



