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Proceedings of the Royal Society of Edinburgh. [Sess. 
continued to increase, the maximum being reached near 86° ; it again fell 
rapidly till about 77°, when the rate of decrease diminished, but the 
modulus was always higher than at the same temperature with the 
increasing current. On allowing the wire to cool to the temperature of 
the room, there was again, as with the other metals, a permanent increase 
in the value of the modulus. 
A Comparison of the Results. 
On reviewing the effects on the metals, we find there are likenesses and 
differences. With weak currents the initial effect on iron, steel, and copper 
is a decrease in the modulus ; while, on the other hand, there is an increase 
in the platinum with even the weakest current that was used 
In all cases, an increase in the strength of the current produced a rise 
in the modulus until a maximum value was attained, the maximum being 
at different temperatures for the different metals. A further increase in 
the current then produced a fall in the modulus, which, in each case, was 
continued up to the highest temperature to which the experiment was 
carried. 
With a diminishing current the effects were more varied. In two 
cases — viz. the iron and the platinum — there was at first a decrease in 
the modulus, but a marked difference between them soon made itself 
manifest. The modulus of the iron was always less than that at the same 
temperature with the increasing current, while, on the contrary, the 
modulus of the platinum rose rapidly, and attained a higher value than 
it had at any temperature with an increasing current. 
On the other hand, when a diminished current was passed through 
steel and copper, the modulus rose in value, and with both a maximum 
was reached which, in the steel, was higher than the maximum with the 
increasing current, whereas, in the copper, it was less than the maximum 
with the increasing current. 
In the iron and the steel, the final values with the current were less 
than the initial values, although the temperatures of these final readings 
were higher than the initial temperatures with a current ; so that the 
effect of a weak diminishing current is, while it is still passing, to produce 
a diminution in the modulus. The result, so far as the experiment was 
carried, was the same with the copper ; the value was less than at the same 
temperature with the increasing current, but, at the lowest temperature at 
which a reading was taken with the diminishing current, the modulus was 
higher than the first reading with a current. The platinum, however, 
