674 Proceedings of the Royal Society of Edinburgh. [Sess. 
decrease. This, again, is in harmony with my results, for when I heated the 
wire in the ordinary way the decrease in the modulus was uniform. It also 
confirms my argument that those conditions which affect the rigidity of a 
substance produce a similar change in Young’s modulus. Since, then, there 
is a diminution both in the rigidity and in Young’s modulus when the sub- 
stance is heated in the ordinary way, it is to be expected that, since an in- 
crease in the magnetic field produces an increase in the rigidity, it will have 
the same effect on Young’s modulus. 
There are other papers dealing with the effects of temperature and 
magnetic field on elasticity, among which may be cited those of Wertheim,* 
Pisati,*)* Katzenelsohn,j Hopkinson and Roger, § Day,|| and Hopkinson.11 
The first three deal with the effect of temperature on the modulus ; they 
all employ the ordinary method of heating. Hopkinson and Roger’s paper 
also discusses the same question, but in their case the temperature was 
raised to nearly 800° C., the rod being heated in an electric furnace. Hay, 
on the other hand, examines the effect of a magnetic field on rigidity, while 
Hopkinson deals with the effect of temperature on the magnetic quality 
of iron. 
Turning again to the graphs of the electric heating with the smaller 
load, it seems possible that the effect may be connected with the Villari 
reversal. In that phenomenon, when the field is weak, a tension on the 
wire increases the susceptibility, but reduces it when the field is strong. 
Now, in my experiments there is an increase in the modulus when the 
current is weak and the tension moderate, so that the increase in the 
susceptibility and in Young’s modulus seem as if they might be connected 
with one another. When the wire is subjected to a greater stress my 
experiments show that there is no such increase in the modulus, and this 
also is in agreement with a longitudinal stress in a magnetic field, for 
Ewing,** in describing the effects of longitudinal pull on iron, says, “ In the 
case of a hard metal, where it is possible to apply a stronger pull without 
permanently altering the characteristics or structure of the piece, it appears 
that the presence of a sufficiently great amount of stress may be unfavour- 
able to magnetisation, even in the earliest stages of the magnetising process.” 
On the other hand, it may be that there is no direct connection between 
* Ann. Ghim. Phys ., (3) vol. xii., p. 385. 1844. 
t Gaz. Ghim. ital ., vol. vii., p. 1. 
X Beiblatter , xii., p. 307. 1888. 
§ Proc. R.S., 1905, p. 419. 
|| Am. Journ. Sc., vol. iii., p. 449. 
IF Phil. Trans., 1889, A., p. 443. 
** Magnetic Induction in Iron, 3rd ed., p. 209. 
