Claude (C. R., 1899, 129, 409) found that for considerable inductions (B =15,000) the permeability and hysteresis-loss remained nearly constant down to - 186°; for weak inductions both notably diminished with temperature.
In many experiments, however, different inductions and frequencies are employed, and the hysteresis-loss is often expressed as ergs per cubic centimetre per cycle and sometimes as horse-power per ton.
The hysteresis-loss in Swedish iron was decreased for inductions below about 9000 and increased for higher inductions; in tungsten-steel, nickel and cobalt the hysteresis-loss was always increased by cooling.
Steinmetz's formula applies only for very weak inductions when the alloys are at the ordinary temperature, but at the temperature of liquid air it becomes applicable through a wide range of inductions.
The fact warns us against drawing hasty inductions as to relative dates from style and execution.