348 Peirce — Induction Coefficients of Hard Steel Magnets. 



slightest degree. In most cases it was not necessary to grind 

 the cylindrical surface true. 



The hardened steel was either exposed to steam at 100° C. 

 or immersed in boiling water for a long time, in order to 

 " relax " the temper in the manner proposed bj Messrs. Barus 

 and Stronhal,"^ and each piece was then very slightly oiled 

 while still hot. After this treatment the steel would still cut 

 ordinary hard window glass. 



The pieces were magnetized between the poles of a soft iron 

 yoke in a long solenoid, having 32 tarns of wire per centimeter 

 of its length, by a current of about 25 amperes. By this 

 arrangement it was possible to force through every pieces of 

 steel at least 18,000 lines of induction per square centimeter of 

 the cross section. 



The magnets were finally " seasoned," according to the direc- 

 tions of Messrs. Barus and Strouhal, by a second long exposure 

 to boiling water or to steam at 100° C. Some magnets thus 

 prepared have been repeatedly thrown upon the floor and one 

 received about a hundred smart blows on end from a bar of 

 magnetized steel without any perceptible loss of permanent 

 magnetic moment. 



A hundred magnets of the same size made in this way of 

 the same kind of steel would be almost indistinguishable, but 

 the inside of a thick piece of steel is evidently left a little 

 less hard than the outer skin. The rate of change (with the 

 length) of the specific magnetic moment of a very short 

 seasoned magnet of given large cross section, sometimes de- 

 creases slightly as the length increases, and, in the case of some 

 comparatively long pieces of thick steel, magnetization, con- 

 trary to the general rule,f increases the induction coefficient. 

 It is easy to get various specific moments and great differences 

 in the effective lengths of magnets of the same actual size 

 made of steel wire hardened in a bundle. 



Because most of the measurements of induction coefficients 

 which I found recorded:]: were made either with unseasoned 

 magnets or with magnets very different in shape from those 

 which I was to use, I felt compelled not only to determine 

 directly the induction coefficients of all the deflecting magnets 

 but to test a large number of magnets made of other kinds of 



*Bulletm of the U. S. Geological Survey. No. 14, 1885 



\ Ewing: Magnetic Induction in Iron and other metals, ch. vi. 



Rayleigh: Phil. Mag., 18S7. 

 :j:Kupffer: Pogg. Ann., 1828 

 Lament: Ann. d. Meteorologie und d. Erdmagnetismus, 1842. 



Handbuch des Krdmagnetismus, 1849. 

 Wild: Ann d. physikalischen ('entral-Observatoriums* 18'78. 



Bulletin d. I' A cad. Imp. d Sc. d. St. Petersbourg, 1880, 1883. 

 Repertorium fur Meteorologie, 1883. 

 Mem. de I'Acad Imp. d Sc. d. St. Petersbourg, 1886. 

 Kohlrausch: Wied. Ann., 1884. 



Nachrichten d. k. Gesellschaft d. "Wissenschaften, Gottingen, 

 1883. 

 H. Sack: Inaugural Diss., Frankfurt, 1886. 



