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PROFESSOR C. H. LEES: THERMAL AND ELECTRICAL 
Standardisation of Resistance Bridge. 
The standardisation of the resistance bridge used in determining the resistances of 
the temperature coils during a conductivity experiment was effected by substituting 
standard coils of O'l, 0'2, 0‘5, DO, and 2'0 ohms for one of the temperature coils, 
and adjusting the bridge to a balance as in the experiments. 
The standardisation of each of the resistances of the dial used in the measurement 
of the difference of the resistances of the two platinum coils, from which the 
difference of temperature of the two points x A and ,r B of the test bar is calculated, 
was effected by substituting for it a standard coil of 0'01006 ohm by Hartmann 
and Braun, and examining the effect of the substitution on the balance of the 
bridge. 
The resistance, 0T055 ohm, found by adding together the resistances of the ten 
coils found in this way, agrees very well with the value 0'1057 found by direct 
comparison of the dial with a Wolff OT-ohm standard after the experiments were 
completed. 
In the tables of observations which follow, the values of the resistances given are 
the corrected ones. 
Standardisation of Ammeter and Voltmeter. 
The Weston milliamperemeter No. 5491, which was used throughout the work to 
measure the current through the coil in which the heat was generated, was 
standardised by comparison with a Kelvin balance which had been checked by the 
copper voltmeter. It was found to read 1 per cent, too high. The values of the 
current given in the following tables are the corrected values. 
The Keiser and Schmidt moving-coil voltmeter was compared by a potentiometer 
method with a cadmium and a Clark cell, either separately, in series, or in opposition. 
The electromotive force of each cell had been determined by comparison with 
a standard Clark. It was found to read 0'8 per cent, too high. The values given in 
the following tables are corrected values. 
Determination of the Coefficient “ h ” of Loss of Heat from the 
Surface of the Rod. 
The final expression for the thermal conductivity k of the material of the rods, 
equation (18), p. 396, involves a knowledge of h, the heat lost in 1 second from 
1 sq. centim. of surface of the bar when that area is 1°C. hotter than the surrounding 
tube. As the terms involving h only affect the result to a small extent, an 
approximate value of the quantity is sufficient. 
To determine this value, the heating coil and upper temperature measuring coil 
were placed on a brass rod 5'2 centims. long, so as to divide the rod into three equal 
