METEORIC AND ARTIFICIAL NICKEL-IRON ALLOYS. 
41 
were obtained if the material was allowed about two hours in which to acquire the 
temperature at which the measurements were to be made—the heating current being 
gradually increased to the necessary value. After the temperature, as shown by the 
resistance measurements, had remained practically constant for about half an hour, 
the throw due to induction in the standardising current was observed. The throws 
due to induction in the ring were measured after this, because they would be affected 
more by want of steadiness in the state of the ring. Finally the throw due to the 
standardising solenoid was checked and the temperature of the ring again noted. 
In some of the later experiments, in which the time at disposal was more limited 
and it was necessary to get observations at a comparatively large number of points in 
succession, it was found that, if precautions were taken to reduce the rate of loss of 
heat by the ring, consistent results could be obtained, at moderately high tempera¬ 
tures, within an hour after the closing of the heating current circuit. In such cases 
the question whether there was a time effect was relatively unimportant. 
§ 2. The majority of the temperature permeability measurements were performed 
under the influence of a constant field. In the earlier measurements the variation of /x 
with H was observed for values of H between 0'4 and 0’8 C.G.S. units ; but the results 
of these observations, which are omitted from considerations of space, seemed to show 
that the information to be derived from them was not likely to be much greater than 
that derived from measurements under a constant field. The experiments were 
performed in the intervals between other work, and it would have been impossible to 
determine BH curves satisfactorily, over a wide range of values of H, in the time at 
disposal. It was therefore decided to aim only at fixing as accurately as possible, in 
the time available, the relation between the permeabilities at different temperatures, 
keeping the intensity of the field unchanged. The demagnetisation of the ring, 
observation of the inductive effect, and measurement of the resistance of the ring 
secondary were repeated in every case (sometimes as often as ten times) till there 
seemed no room for doubt that truly corresponding values of induction and tempera¬ 
ture had been obtained. 
§ 3. The data obtained from the experiments with the different materials are 
collected in the tables which follow. 
VOL. CCVIII.— A, 
Gr 
