200 
Proceedings of the Royal Society of Edinburgh. [Sess. 
Steel. 
A wire of the same gauge as in the preceding experiments was used, 
and was put through successive cycles of heating and cooling, the loads 
being 1*1, L4, 1*7, and 2*0 kilos. The resulting curves are shown in fig. 7, 
each one being that obtained after the cyclic state had been reached. It 
will be seen that the modulus diminishes as the weight is increased, that is, 
at the same stage in any two cycles the modulus has a greater value in 
that cycle in which the load is smaller. 
Speaking generally, we are able to say, from a comparison of the curves 
obtained under similar conditions — e.g. figs. 4 and 7, 5 and 8, 6 and 9 — that 
effects of an electric current on Young’s Modulus are the same in steel as in 
iron. At the same time, there are certain differences, for it will be seen 
that, when the current is diminishing, the curves at first lie above those at 
the same temperature for increasing current. Again, as the load is increased, 
the value of the modulus falls, and the maximum value is also reached in a 
weaker field, a result similar to what was found for iron. 
An examination of the curves when the current was kept constant, and 
the load varied, shows that the curve for unloading is at first higher than 
that for loading, a point in which steel differs from iron. It is also seen 
that increase of field produces at first increase in the modulus, but that, 
when it rises above a certain value, a further increase causes the modulus 
ito diminish. In the highest field there is a uniform decrease, and the curve 
'becomes a straight line. 
Steel. 
Length — 98’42 cms. 
Area of cross-section = '0004714 sq. cm. 
Elongation weight = 500 grams. 
Total load on wire = IT kilos. 
Load per sq. mm. = 233 kilos, per sq. mm. 
Table Y. 
No. 
Temp. 
Elongation for 
500 grams. 
No. of 
Observations. 
M. 
1 
14°8 C. 
•04835 cm. 
8 
21T9 x 10 11 
2 
20-2 
•04812 
9 
21-29 
3 
263 
■04792 
9 
21-38 
4 
300 
■04781 
10 
21-43 
5 
334 
•04776 
8 
21-45 
6 
36-9 
•04776 
8 
21-45 
