566 



Drs. De La Rue and H. W. Miiller. 



[June 17^ 



The diagram, fig. 3, will illustrate the action of the special key, 

 fig. 1. When the handle is moved to the left, the tube TT' is placed 



Fig. 3. 



t' 



in metallic connexion with the battery, whose terminals are shown 

 attached to c and d (this is equivalent to the springs being allowed to 

 press upwards against c and d, fig. 1) ; when the handle is moved 

 to the right, then the discharge of the battery through TT' ceases, 

 and the terminals of the tubes N and P are connected with the galva- 

 nometer, the extremities of whose coil are attached to e and / (this is 

 equivalent to pressing down the springs in fig. 1). 



On another occasion with the same tube, No. 73, with a discharge 

 from 2,400 cells, the deviation to the left on passing down e and /was 

 20 divisions. 



Tube 199, with a hydrogen charge, was now substituted, fig. 4 ; 

 pressure 2 millims., 2,632 M, 5,100 cells, current 0-01639 W. This 

 tube has already been described ;* it is 37 inches (94 centims.) long, and 

 inches (14*8 centims.) in diameter. The distance between the 

 terminals, a ring and a straight wire, is 33*5 inches (85 centims.). In 

 the first place the battery was connected direct to the galvanometer, 

 the positive to e and the negative to f (that is, in the same direction as, 

 if the positive were attached to c and the negative to d). A short 

 piece of wire was inserted between e and / as a shunt, and the 



* " Phil. Trans.," vol. clxxi, p. 104. 



