336 B. 0. Peirce — Properties of Seasoned Magnets. 



tested were away : M , the moment of the last named magnet 

 at the temperature t , at which the adjustments have been 

 made; and M, the moment of this magnet when, its tempera- 

 ture having become t, the needle is deflected through the 

 M— M tana 



an s lea ' ir = ^' 



The strength of the field around the magnetometer needle could 

 be modified at pleasure, and in this way great sensitiveness 

 obtained. The change of moment caused by a change of 

 temperature of a small fraction of a degree, even in the case 

 of the shortest magnets used, could be easily measured when 

 the center of the magnet was many times the length of the 

 magnet away from the magnetometer. 



If any one of my magnets which had not been heated above 

 room temperatures for some time, was heated to 100° and then 

 brought back to the room temperature, it did not immediately 

 regain its original moment, and in the case of some magnets 

 this temporary loss seemed to be greater than any which Mr. 

 Durward noticed in the case of tool steel magnets. Upon 

 reheating the magnet to 100°, there seemed to be little if any 

 addition to this temporary loss, and the moment passed through 

 a cycle when the temperature* returned to its old value after 

 going through any succession of changes. Whatever the 

 previous history of a magnet had been, a sudden increase in 

 temperature was accompanied by a sudden, not a gradually 



Table I. 



Eesults of observations on a 

 seasoned magnet 8 cm long made 

 of Jessops Square Self-Harden- 

 ing Tool Steel. 



Dimensions of cross section, 

 0-96 cm x0-96 cm . 



Table II. 



Results of observations on a 

 seasoned magnet 6 cm loug made 

 of Mushet Square Self-Harden- 

 iug Tool Steel. 



Dimensions of cross section, 

 0-96 cm x 0-96 cm . 





Loss of magnetic 





Loss of magnetic 





moment in terms 





moment in terms 



Temperature. 



of the moment, 



Temperature. 



of the moment, 





M , at 1-1° C. 





Mo, at 7-2° C. 



7-7 



o-oooo 



7-2 



o-oooo 



12-0 



0-0028 



120 



0-0048 



20-0 



0-0087 



20-0 



0-0140 



30-0 



0-0J71 



30-0 



0-0275 



40-0 



0-0259 



400 



0-0420 



50-0 



0-0353 



50-0 



0-0580 



60-0 



0-0448 



60-0 



0-0805 



70*0 



0-0559 







80-0 



0-0683 







90-0 



0-0825 







100-0 



0-1016 







increasing, fall of moment and the rate of the fall per 



