XIV. Magnetic and other physical properties of iron at a high temperature
It is well known that for small magnetising forces the magnetisation of iron, nickel, and cobalt increases with increase of temperature, but that it diminishes for large magnetising forces. Bauer has also shown that iron ceases to be magnetic some what suddenly, and that the increase of magnetisation for small forces continues to near the point at which the magnetism disappears. His experiments were made upon a bar which was heated in a furnace and then suspended within a magnetising coil and allowed to cool, the observations being made at intervals during cooling. This method is inconvenient for the calculation of the magnetising forces, and the temperature must have been far from uniform through the bar. In my own experiments on an impure sample of nickel the curve of magnetisation is determined at temperatures just below the temperature at which the magnetism disappears, which we may appropriately call the critical temperature. Auerbach and Callendar have shown that the electrical resistance of iron increases notably more rapidly than does that of other pure metals. Barrett, in announcing his discovery of recalescence, remarked that the phenomenon probably occurred at the critical temperature. Tait investigated the thermo-electric properties of iron, and found that a notable change occurred at a red heat, and thought it probable that this change occurred at the critical temperature.