380 
MR. C. CHREE OR THE EFFECTS OF PRESSURE 
or non-polar effect. It is obvious, however, that if the magnetic molecules sowing 
round and stuck in the way imagined, then the magnetisation would naturally be 
greater in a field of the same sign as the original than in a field of opposite sign. 
This is not regarded here as a true polar effect, though producing in the induced 
magnetisation phenomena identical with those which would arise from a true polar 
change in the molecular mobility. The turning round of the molecules has been 
already discussed in §§ 22 and 28, where its occurrence was demonstrated. The effect 
on the induced magnetisation will here be referred to as a quasi polar effect. 
§ 65. The ninth column of Table IX. may be regarded as measuring the combined 
true and quasi polar effects of a numerous series of pressure cycles, in so far as they 
survive the break of the field during which the pressures were applied, and the make 
of an equal field of the same or opposite sign. The exact quantity measured is the 
algebraic excess of the magnetisation in a field of the same sign as that existing 
during the pressure cycles over that in a field of opposite sign, the rod being in each 
case introduced free of pressure into the second fields. 
The results obtained with the weakest field of the table, 1'8 C.G.S. units, differed 
so much from the others that it was inconvenient to include them in the table. They 
were as follows :— 
Circumstances of rod. 
End a 
north pole. 
Pressure. 
3. 
First introduction .... 
A 
off 
4T 
After pressure cycles . 
55 
55 
6'5 
Out, re-introduced. 
B 
4-8 
Kept in. 
55 
on 
6-5 
Out, re-iutroduced. 
6-2 
A 
off 
4T 
51 55 .... 
B 
55 
5-5 
55 55 ...» 
A 
4-1 
Kept in. 
55 
on 
6-5 
Out, re-introduced. 
off 
5 3 
55 . 55 .... 
B 
55 
5T 
There are here two or three instances of an increase of susceptibility of a non-polar 
character, and also clear indications of a polar effect. Considering how small the 
total induced magnetisation is, both the polar and non-polar effects are of consider¬ 
able importance. 
In the next field, 2’2 C.G.S. units, the rod was originally under pressure, and yet 
%2 ~ 3i exceeds Sg — %. Thus, as 3 a — 3b is only '2, there occurred a very decided 
residual increase of susceptibility, mainly of a non-polar character. 
In all the fields, from 3'4 to 35'7 C.G.S. units, the residual effect is largely of a 
polar character. Take, for instance, the field 8'6. Here the pressure cycles raise the 
magnetisation by 10'2. Of this, 5T survives the break and re-make of the current, 
and so only about the half of the increase is lost. 
