832 
MR. H. TOMLINSON ON THE INFLUENCE OF STRESS AND 
and the difference in the two logarithmic decrements is not greater than could be 
accounted for by slight difference in the steadiness of the temperature.* Two nickel 
wires, whose diameters were also nearly in the same ratio, namely 2:1, gave values 
for the logarithmic decrements due to internal friction which agreed with each other 
within the errors of observation. 
Experiment XXII. 
Two pieces of the same specimen of annealed zinc wire, one 602 centims. in length 
and the other only 97 centims. in length, were both tried under nearly the same con¬ 
ditions as regards preliminary treatment and time of vibration, &c. The logarithmic 
decrement due to internal friction was, in the case of the longer wire, '003207, and, 
in the case of the shorter one, '003327. The difference between these two numbers 
can quite be accounted for by the fact that the temperature of the shorter wire was 
about 3° C. higher than that of the longer.! 
Two pieces of iron wire, cut from the same hank, but one having a length of 
96 centims. and the other of 602 centims., gave, when treated in a similar manner, 
exactly the same logarithmic decrements. 
We may, therefore, regard the logarithmic decrement as independent both of the 
length and of the diameter of the wire, provided care be taken that the tw r o pieces 
of different lengths which are compared shall have suffered the same preliminary 
treatment. 
“ Fatigue of Elasticity 
Sir William Thomson writes,^ “ Experimental exercises performed by students in 
the physical laboratory of the University of Glasgow, during the session 1864-65, 
brought to light some very remarkable and interesting results, proving a loss of energy 
in elastic vibrators incomparably greater than anything which could be due to imper¬ 
fections in their elasticity, and showing also a very remarkable fatigue of elasticity, 
according to which a wire, which had been kept vibrating for several hours or days 
through a certain range, came to rest much more quickly when left to itself than 
when set in vibration after it had been at rest for several da}^s and then immediately 
left to itself.” This so-called “fatigue of elasticity” seemed to me such a very 
remarkable phenomenon that, throughout the whole of these investigations, I was 
constantly on the look-out for traces of it; but, owing no doubt to the very slight 
maximum deformations employed in these experiments, I could detect nothing of the 
kind with any metal § except nickel. The whole of the other metals examined, namely, 
* It is necessary to take great care that the temperature should fluctuate very little, as any fluctuation 
will affect a thin wire more than a thicker one. 
| The effect of change of temperature on the internal friction of zinc is rather considerable. 
J ‘ Encycl. Brit.,’ 9th edit., Art. “ Elasticity,” § 30. 
§ Except in Experiment XIX. 
