B. 0. Peirce — Properties of Seasoned Magnets. 335 



induction bench (figure 1) before and after they had been 

 exposed to steam at 100° C. for hours in the manner suggested 

 by Messrs. Barus and Strouhal. The results given in Tables 

 III and IV show that the long-continued heating did produce 

 a slight "relaxation" of the metal. 



The pieces of steel were then magnetized between the poles 

 of a soft iron yoke in a large solenoid carrying a current of 

 25-35 amperes. The semi-permanent moments which they 

 acquired in this way were, however, much reduced (as maybe 

 seen by comparing the figures given in columns 2 and 3 of 

 Table V) by boiling them for a long time in water and thus 

 seasoning them. I expected that a number of long, seasoned 

 magnets of given dimensions made in this way would be more 

 nearly alike than a set of similar magnets made of tool steel, 

 in the case of which the difficulties of uniform hardening are 

 so great ; but in this I was disappointed. Occasional very 

 abnormal specimens occurred. A magnet seemingly like its 

 neighbors would show a very low moment and at the same 

 time temperature and induction coefficients 30 per cent or 

 more above the others, which would prove to be nearly alike. 

 An attempt to remedy these defects by remagnetizing the steel 

 failed. I have assumed that a normal magnet is characterized 

 by a high magnetic moment and low temperature and induction 

 coefficients, and, although I could not prove, as in the case of 

 tool steel, that all abnormal magnets were either soft in places 

 or cracked, I rejected all such without question. 



The temperature coefficients* were determined in a piece of 

 apparatus described by Mr. Arthur Durward in his paper " On 

 the Temperature Coefficients of Certain Seasoned Hard-Steel 

 Magnets." The magnet to be experimented upon was fixed 

 firmly in a non-magnetic holder inside a non-magnetic tube so as 

 to be in Gauss's A Position east of a mirror magnetometer. By 

 the help of an elaborate system of pipes constructed by Mr. J. 

 Connors of the staff of the Jefferson Laboratory, tap water, 

 steam, or a stream of water from a bath-water heater at almost 

 any desired constant temperature between 15° and 100°, could 

 be sent through the tube surrounding the magnet. On the 

 west of the magnetometer, so placed in Gauss's A Position as 

 to bring the needle back into the meridian, was a short, 

 seasoned, compensating magnet fixed within a wooden holder 

 and completely shielded from sudden temperature changes. 

 If M' is the moment of the compensating magnet ; a , the 

 needle deflection which it would cause if the magnet to be 



*Cr. Wiedemann, Pogg. Ann., 1852, 1858. 1864; Dufour, Arch, de Geneve, 

 1857 : Lamont, Handbuch d. Magnetismus, 1867; Barns and Strouhal, Bulletin of 

 the U. S. Geological Survey. No. 14, 18&5; F. Kohlrausch, Wied. Ann., 1884; 

 Cancani, Atti Ace. Line, 1887. 



