ON THE MAGNETISATION OF COBALT. 
361 
§ 36. In Table IX. the first six headings have been already explained. The letter 
after the numerical measure of the field in the first column signifies that the rod was 
under pressure previous to and during its introduction into the coil. In such a case 
the entries under 3^ and /c^ refer to the magnetisation existing before this pressure 
was removed, and so are on a different footing from the other entries under these 
headings. The entries under the other headings are also in such a case doubtless 
indirectly affected, but to a much smaller degree. 
In the last four headings the suffix indicates which end of the rod was the north 
pole when the magnetisation in question was measured. The results under these 
headings are deduced from the readings obtained by removing and replacing the rod 
subsequent to the application of the pressure cycles, during which application it must 
be remembered A was always the north pole. 
The seventh column gives the excess of the magnetisation existing when the rod 
was under pressure wdien reintroduced into the coil over that existing when it was 
free from pressure when reintroduced, the end A being in each case the north pole of 
the reintroduced rod. The eighth column differs from the seventh only in that the 
end B was in each case the north pole of the reintroduced rod. The ninth column 
gives the excess of the magnetisation found when A wms the north pole of the 
reintroduced rod over that found when B was the north pole, the rod in each of its 
reintroductions being free from pressure. The tenth column differs from the ninth 
only in that the rod during each of its reintroductions was under pressure. 
§ 37. In Table X. Fiist “ on ” is, as previously, the total change in the magnetisa¬ 
tion—cyclic and non-cyclic—due to the first application of pressure. Aj^ gives the 
effect when the rod, immediately after being demagnetised, has been exposed for the 
first time to the field in question. Ag gives the effect of the first pressure applied 
after the reintroduction of the rod in a state free from pressure, and with the end A 
a north pole. In the case of the results under Aj, there have intervened since 
demagnetisation a complete series of pressure cycles applied with A a north pole, a,nd 
at least one removal and reinbroduction of the rod. In some cases there were several 
removals and reintroductions, and the mean of the observations is recorded. Under 
Bg we get the effect when, on its reintroduction, the rod has B for its north pole. In 
this case it must be borne in mind that the pressure cycles applied since the preceding 
demagnetisation occurred when the opposite end A was the north pole. 
First “ off" is the total effect of the removal of a ])ressure existing previous to and 
during the introduction of the rod into the coil. A^ refers to the case when demagne¬ 
tisation has immediately preceded the observation, Ag and Bg to the cases when a 
complete series of pressure cycles, with A the north pole, and at least one removal and 
reintroduction have intervened since demagnetisation. The distinction between A 
and B is the same as in the case of the First “on” 
Cyclic “on” — “ off” has its usual meaning. Under the next two headings are given 
the non-cyclic portions of the effects of the first application of pressure and of the first 
MDCCCXC. -A. 3 A 
