296 H. E. J. G. du Bois on Magnetization in 



attempted to compensate the very considerable action of the 

 coil alone by that of another similar one, placed due west and 

 in the same circuit. Great difficulty was experienced with 

 this, principally due to heating of the coils and parasitic action 

 of distant current leads. Finally the idea of total compensa- 

 tion had to be given up, and the remaining difference was 

 each time carefully determined and corrected for. The earth's 

 horizontal intensity at the magnetometer's site w T as measured 

 once for all ; its fluctuations being followed with one of Prof. 

 F. Kohlrausch's local variometers. Thus the magnetic 

 moments of the ovoids could be accurately obtained in abso- 

 lute measure. 



§ 5. Preliminary trials. — I began by trying whether there 

 was a perceptible influence of magnetic history in general ; or 

 of the hysteresis, due to its latest phases, in particular. The 

 ovoids were therefore made to pass through various magnetic 

 ordeals, as descending or ascending currents, reversals, &c. 

 None were found, however, to have an appreciable effect, except 

 with fields below 150 C.G.S., say, where such an influence 

 occurred, though slightly. The reasons for this are no doubt: — 

 (1) the ovoids had too little of endlessness to exhibit much 

 hysteresis in any case ; (2) the slightly pulsating machine- 

 current effectually counteracts it by its shaking action ; and 

 (3) probably hysteresis really comes less to the foreground 

 with such strong magnetizing fields. 



However this may be, I was thereby free to magnetize in 

 whatever manner I chose ; as a rule, two magnetometer- 

 readings were taken with currents reversed. The moment for 

 a given temperature may thence be plotted in a loopless curve 

 as a function of ,ff only, provided the latter exceed 100 C.G.S. 

 say. Neither was I sensibly troubled with the well-known 

 acyclic shaking-in action of temperature- variations ; perfectly 

 consistent results being obtained with strong fields whether on 

 heating or on cooling. Accordingly the moment due to a 

 given magnetic intensity may be considered a function of the 

 temperature only. 



§ 6. Magnetic curves. — After much hesitation I decided 

 not to plot 3 as usual, but the specific magnetization ©. The 

 principal reason for this was that the results became more 

 comparable by thus eliminating the density, which depends on 

 temperature and other physical conditions of the material, and 

 could moreover not be determined for the electrolytic metals 

 tested (§ 8). In fact, magnetism being an essentially mole- 

 cular phenomenon, it is for certain purposes more rationally 



