404 
MESSRS. W. E. AYRTON AND H. KILGOUR ON THE 
of about 308° C. The error, therefore, which we have made in assuming that the 
whole length of 27‘46 was at 314° C. was not serious. 
Fig. 16. 
0 2 4 6 8 10 12 14 16 IS 20 22 24 26 28 O0 
<--- Total lenuth.oj' were measur-ed. fram. one encl -> 
And, a fortiori, the lengths which were employed with all the finer wires in the 
emissivity experiments and the position of the voltmeter wires, were such that the 
temperature was practically constant over all the length of the wire used in the 
emissivity calculations. 
In the case of the wires thicker than 6 mils, the error arising from the conduction 
was necessarily greater; and the calculations that w r e have made on the distribution 
of temperature along the 6-mil wire have led us to the conclusion that, if we were 
going to repeat the experiments, we should, in the case of the thickest wires 
employed, attach the voltmeter wires at about 2 centims. from the supports. We do 
not, however, think that any serious error has been introduced by attaching them at 
only about 7 millims., except, perhaps, in the case of the largest currents with the 
largest wires. 
When plotting the curve for d'H/dx 2 given in fig. 15, it was noticed that this curve, 
where it cuts the axis along which dHjdx 2 is reckoned, was not strictly parabolic. 
Professor Hekrici suggested that an idea might be obtained of the error ntroduced, 
by assuming the lower portion of this curve to be parabolic, if a tangent were drawn 
to the true curve for dH/dx 3 at about t equals 315° C., and if calculations were made 
on the assumption that this tangent line were itself the curve for dH/dx 2 . 
Doing this, we obtain the following equation by integration for the temperature 
curve 
where T, as before, is 315 C C., and where b is minus the value of the ordinate of this 
tangent when t equals nought. When measured, b is found to be 2388. 
