IRON AND STEEL IN A ROTATING MAGNETIC FIELD. 
739 
been pushed far enough, but so far there is no sign of any large amount of frictional 
control. This is noteworthy, as we are accustomed to consider the steel molecules as 
subject to some form of mechanical constriction. 
In Diagram 10 are given the mean values of the curves obtained for iron and steel, 
the latter being plotted with a smaller vertical scale to admit of easier comparison. 
With them are also plotted the curves of hysteresis in an alternating field, that for 
soft iron being obtained by a calorimetric method with iron from the same sample. 
(‘Electrician,’ November 22, 1895.) 
Part II. 
Effect of Speed on Hysteresis. 
The question of the relation between the speed of reversal of magnetization and 
the value of the hysteresis per reversal has been investigated by several experi¬ 
mentalists, by the employment of an alternating current of varying periodicity. 
The experiments of Tanakadate (‘Phil. Mag./ September, 1889) by the calori¬ 
metric method, indicate that there is no change in the hysteresis between the values 
27 and 400 cycles per second. His method, however, is liable to error, and he does 
not measure the induction at the same time as the hysteresis, but finds it by a 
ballistic test. As his magnetic circuit has only a small reluctance and no air gap, 
this assumption of identity is doubtful. 
The experiments of Mr. A. Siemens (‘ Proc. I.E.E.,’ February, 1892) and Mr. C. P. 
Steinmetz (‘E.T.Z.,’ 1891 and 1892, and ‘ Electrician,’ February, 1892) indicate a 
change of hysteresis in this respect, but their results are not consistent. By the 
magnetic curve tracer Professor Ewing has made some tests at low speeds, but the 
presence of eddy currents in the pole pieces obscure the results, and mechanical lag 
and vibration in the moving parts prevent the use of any but very moderate speeds. 
Dr. John Hopkinson (‘Electrician,’ loc. cit .) finds that in hard steel wires, while the 
permeability is not changed, there is a small increase in the hysteresis as the speed 
is increased. The experiment is, however, obscured in regard to this point by the 
changes in the form of the current curve consequent upon change of speed. Mr. T. 
Gray (‘ Boy. Soc. Proc.,’ May, 1894) finds no variation in the hysteresis between the 
speeds of 3 and 8,000 cycles per minute, but his experiments are somewhat con¬ 
tradictory. Becently the author has shown (‘Electrician,’ Joe. cit.) that the change 
of hysteresis, if it exists at all, must be very slight and that on theoretical grounds 
it is probably independent of speed. 
In the foregoing experiments with a rotating field it has been indicated that there 
is at most very little change of hysteresis at different speeds. The point v r as more 
carefully worked out as follows :— 
5 B 
O 
4 
