166 MR. J. H. GRAY ON A METHOD OF DETERMINING 
the thermal conductivity. It will be noted that this value is the proper mean 
conductivity corresponding to the range of temperature between the ends of the wire. 
Fig. 1 is a perspective drawing of the apparatus which has been used in the tests 
of this method. Fig. 2 is a section (all the parts being drawn quarter full size) 
containing the axis of the wire to be tested. Fig. 3 is a section, drawn full size, 
through the middle of the apparatus, in a plane perpendicular to the section in fig. 2, 
and showing in greater detail the wire, calorimeter ball, and that part of the heating 
box at which the wire is soldered. 
Fig. 1. Fig. 2. 




































2 3 
_——— 
AWS 
Quarter full size. 





Referring to fig. 2, W is the wire to be tested. The upper end of W is soldered 
into the bottom of the copper box B, and the lower end into the solid copper ball C, 
the diameter of which is 5°5 centims. The sides of the copper box B are of thin 
sheet copper, and the bottom of copper, 3 millims. thick. B is supported at the 
middle by being fitted into a rectangular hole in a wooden screen, L, of dimensions 
60 X 60 centims., by 2 centims. thick. In the hole of the copper block K, a small 
thermometer is inserted for measuring the temperature of the other end of the wire. 
The box B is filled with water and kept boiling briskly. The ball C is the calori- 
meter by which the amount of heat conducted by the wire W is measured. In order 
to measure the temperature of C, a very sensitive thermometer, which can be read to 
one-fortieth of a degree Centigrade, is inserted in a hole drilled in C. This hole 
reaches to a depth of 8°6 centims. from the circumference of the ball. The bulb 
of the thermometer in the ball is surrounded by water or mercury. Surrounding 
