Two Tons produced in Gates by Tt&ntgen Radiation. 125 



electrometer E, which may be connected to earth by the 

 key H. 



G is a plug of glass-wool which serves to make more 

 uniform the stream of gas, and to free it from dust and any 

 electric charge. The rubber tubes D and F lead to two gas- 

 bags, each of a capacity of about 135 litres. By putting an 

 excess weight on the bag connected to D the gas is forced 

 through the apparatus into the second bag. It can then be 

 forced back and be used over again. 



The induction-coil and the tube are situated in a lead- 

 covered box which is connected to earth, and of which C 

 represents the upper part. 



The rays from the source pass through the aluminium 

 window A and into the box P Q through its wooden bottom. 

 By means of the adjustable lead strips L the rays can be pre- 

 vented from impinging upon the plates P and Q, and the 

 amount of gas exposed can be regulated. The plate P is 

 connected to earth while Q is connected to one pole of the 

 storage-battery B, the other pole of which is also to earth. 



When the rays are entering P Q and the ions are travelling 

 in opposite directions in the box, the charges they give to Y, 

 Q, and K are conducted to earth, while those they give to T 

 gradually change its potential, and at an approximately uni- 

 form rate so long as this potential is small compared to that 

 of Q. When the distribution of the free charges in the gas 

 has assumed a steady state, all changes in the potential of T 

 are due to ions giving up their charges to it. 



If a stream of gas is now blown through the apparatus in 

 the direction from T to K, the ions moving against the stream 

 in the direction from K to T travel slower than before, and 

 the potential of T changes less rapidly, 



