431 
1910-11.] Energy in Torsionally Oscillating Wires. 
Diagram 2 shows the condition at 375° C., i.e. the first temperature noted at 
which the double line begins to be necessary, whilst diagram 3 shows a 
decided angle between the two lines. 
Time Effect. 
In these temperature experiments, the plan adopted was to raise the 
brass wire up to the temperature indicated, and to remove it from the fur- 
nace at once, as it was found by previous tests that the change was a sudden 
one. Wires were introduced for J hour, J hour, 5 minutes, and 1 minute, 
respectively, at a temperature of 400° C., and in each case the same values of 
n got. 
Lowering of Temperature. 
A length of original * wire was allowed to remain in liquid air for over 
half an hour and subsequently tested, but this seemed to have no effect on 
the value of n ; and this result was also got on treating in the same manner 
a portion of wire already heated past 375° C. 
Effect of Extensional Strain. 
A length of the original wire was hung with a 14-lb. weight attached 
in a long vertical shaft, and portions cut from it were tested at intervals of 
days or weeks, but no change was observed. The weight was then replaced 
by one of 28 lbs., and latterly of 56 lbs., but still the same values of n were 
observed. The wire after heating to 400° C., however, could be easily elon- 
gated by a pull ; and on subsequent testing it was found to give results 
tending to approach those obtained with an unheated length of wire. A 
wire 12 inches in length was raised to 400° C. and then stretched till 
rupture occurred. The value of a was found to have changed to 100, whilst 
n was found to be 1*34, — the points again all falling into one straight line. 
The diameter was now 090 mm., and the change of length 3 inches. Thus 
stretching is followed by a reversion to the original conditions of the un- 
heated wire ; and it is quite probable that, with more careful stretching, the 
value of n could be reduced to its original amount. The effects of repeated 
extensional and torsional strains on brass are treated in another paper. 
Wires of Varying Diameter. 
It was found that a wire of diameter T2 mms. gave results similar to 
those got for that of diameter 1*0 mm. The exact values got were 
a = 95, n=- 70, 5 = 439. 
* This term will be used in subsequent pages to denote a length of wire cut from a coil 
as supplied by the dealer. 
