374 
MESSRS. W. E. AYRTON AND H. KILGOUR ON THE 
was experimentally determined up to 300° C. The investigation, therefore, divided 
itself into two distinct parts, viz. :— 
A, the measurement of the power required to be given to platinum wires of various 
diameters, so as to maintain them at various temperatures above that of the enclosure. 
B, the determination of the law connecting the resistance wfitli the temperature for 
each piece of wire employed in A. 
Fig. 1. 
And the second investigation also consisted of two parts, since a very considerable 
time had to be finally spent in determining the errors of the thermometers that had 
been employed in measuring the variation of the resistance of the wires with 
temperature. 
Fig. 2. 
For carrying out the first part of the investigation, each wire was placed hori¬ 
zontally along the axis of a water-jacketed cylinder shown in section A, B, C, D 
(fig. 1), 32-5 centims. long, 5‘08 centims. internal, and 7*62 centims. external diameter, 
the interior surface of the cylinder being coated with dull lamp black. A stream of 
water of constant temperature entering by the pipe at _D, and leaving by the pipe 
