194 Mr M c Glung, Investigation of the effect of Temperature 



tightly with wire, and also by heavy rubber compression tubing N 

 and N' adjusted in a similar manner. These joints have also 

 proved very satisfactory. 



General arrangement of Apparatus. 



The general arrangement of the whole apparatus is shown in 

 fig. 2. The cylinder AB was connected through the tube ^'to 

 a mercury pressure-gauge R, and the level of the mercury con- 

 tained in the arm nearest the cylinder could always be brought 

 back to a fixed point Q by means of a mercury reservoir S whose 

 height could be adjusted. By this means the quantity of gas in 

 the cylinder could be kept at a constant volume and density. 

 When the cylinder was heated the amount of pressure exerted by 

 the gas was measured by the height of the mercury column in the 

 arm L of the pressure-gauge. As this mercury gauge was necessary 

 in any case it was utilized also to determine the temperature of 

 the enclosed gas when heated, by observing the. amount of pressure 

 exerted by the gas. This obviated the necessity of introducing an 

 ordinary thermometer into the cylinder and thus the number of 

 joints which had to be made gas-tight was lessened. This method 

 of determining the temperature gave the mean temperature of the 

 gas inside the cylinder. 



The cylinder and enclosed gas were heated by means of an 

 electric current passing through a coil of wire wound closely round 

 the outside of the cylinder. The wire was insulated from the 

 cylinder by means of sheet asbestos. Above the layer of wire 

 there was a covering of asbestos and also of felt in order to keep 

 the heat from radiating as much as possible. By this method 

 the cylinder could be heated up to the maximum temperature, 

 employed quite quickly, and the temperature could also be kept 

 quite steady. 



The electrode E, as shown in the figure, was connected to one 

 pair of quadrants of an electrometer while the other pair was 

 connected to earth. The electrometer used was one of the 

 Dolezalek type, and gave about two thousand scale divisions for 

 a difference of potential of one volt between the quadrants when 

 the needle was charged to 120 volts. The other electrode, E\ was 

 connected to one pole of a battery of accumulators while the other 

 pole was connected to earth. 



The Bontgen ray bulb used in the experiments was one of the 

 focus-tube type, with an automatic vacuum regulator attached. 

 The bulb along with the induction coil was enclosed in a lead- 

 covered box, and the rays emerged through a well-defined rect- 

 angular orifice, as shown in the diagram. Although it worked 

 very satisfactorily, even with one of these tubes the intensity of 



