658 Mr. McClung on the Relation between Bate of 



regulation o£ the temperature was a comparatively simple 

 matter. The temperature of the air which was being experi- 

 mented upon in the cylinder was measured by the two mercury 

 thermometers, T and T', shown in the diagram ; and the mean 

 o£ the temperatures indicated by these two thermometers 

 was taken as the average temperature o£ the air which was 

 being experimented upon. 



The electrode E' was connected to one pair of quadrants o£ 

 the electrometer, the other pair being connected to earth. 

 The electrometer used throughout these experiments was 

 one o£ the Dolazalek type, and gave a deflexion o£ about 

 2000 scale-divisions for a difference o£ potential of one volt 

 between the quadrants when the needle was charged to 

 120 volts. 



The arrangement for making and breaking contacts by 

 means of a pendulum and levers was similar to that used 

 in the previous experiments, and has been fully described in 

 the former paper. In the present instance the contacts were 

 broken by means of a heavy steel-ball pendulum, the ball 

 being suspended by two thin steel wires about three metres 

 long. A pointer on the bottom of the ball struck the ends 

 of the levers as it swung along the path .v i/. The levers L 

 and L' were held in contact with Q and Q' by means of springs. 

 The electrode E was connected through a large liquid re- 

 sistance R, consisting of a solution of cadmium iodide in 

 alcohol, to one pole of a battery of accumulators, the other 

 pole of the battery being connected to earth. 



At the beginning of the investigation a Rontgen-ray bulb 

 was used of the ordinary form, without any vacuum regulator 

 of any sort attached. This, however, did not prove satisfactory, 

 for it w^as inclined to run hard with use, and the intensity of 

 the rays was therefore apt to change during the course of a 

 series of experiments, making it diflicult to obtain consistent 

 results. This bulb was therefore abandoned, and a focus-tube 

 with an automatic vacuum-regulator attached was obtained. 

 This bulb proved much more satisfactory, and was employed 

 throughout the remainder of the investigation. All the 

 results given in this paper were obtained with this bulb. 



Test of the Law of Recombination at Various Temperatures. 

 When equation (1) is integrated it becomes 



«-i^ = ^'' (^) 



where N is the maximum number of ions per c.c. at the 



