ON THE MAGNETISATION OF COBALT. 
351 
demagnetisation, and contained in Tables IX. and X., it appeaios that in those of the 
eight weakest fields of Table I., in which A was a north pole, the values obtained for 
K^, K^, and the cyclic effect are all undoubtedly somewhat too great. 
The effects of the residual polarity appear still more decidedly in Table II. in the 
case of field (14). Here, what must be regarded as an abnormally large amount 
of residual magnetism, was originally present. Every trace of this was, however, 
removed by a single pressure, and with subsequent pressures magnetism of opposite 
sign became apparent. An even more striking case, that of field (13), does not 
appear in Table II. because no absolute measures were taken. In this case, the 
residual magnetism on the break even of the current was of opposite sign to the 
induced, and it increased on the application of pressure. 
Second Series of Experiments. 
§ 29. In the next principal series of experiments—taken in January, 1889—the 
method of taking the observations was much the same as in the first series, but the 
distances between the pieces of the apparatus were varied. Thus the distance 
of the centre of the rod from the magnetometer needle was 73’6 cm., 50 cm., or only 
39'2 cm., according as the quantity under examination was the intensity of the 
induced magnetisation, the effect of pressure on the induced magnetisation, or the 
residual magnetisation. The compensating coil and the scale remained screwed to the 
beam carrying the apparatus, while the three positions of the magnetising coil and 
the corresponding positions of the magnetometer were indicated by pencil marks 
on the beam. There was no shaking of the rod, or variation in the current caused 
by the movements of the coil and magnetometer. 
The fields in this series of experiments varied from 84’8 to 725 C.G.S. units. 
Preliminary experiments in the weakest of these fields, showed that demagnetising 
the rod had no appreciable influence on the magnitude of the cyclic effect of pressure. 
There was thus in none of the recorded experiments, as given in I'ables III. and IV., 
any attempt at demagnetisation ; but the weaker fields were taken first so as to avoid 
the disturbing influence of any residual effects that might originate with very strong 
currents. 
