206 
MR. J. ZELENY ON THE VELOCITY OF THE IONS 
2. The distance of the beam of rays from the insulated juncture in the inner 
cylinder was also changed. This likewise necessitated a change in the value of the 
potential A, but in the opposite sense. The paths of the ions are now quite 
different, and changes are also produced in all of the quantities mentioned in the 
lireceding case. 
3. The intensity of the Rontgen rays was also varied. This produced alterations 
in the density of the free charges in the gas, and consequently in their effect upon the 
electric field between the cylinders and in the mutual repulsion of the ions. The 
amount of the recombination of the ions is also affected as well as the fall of potential 
at the electrodes. 
4. By changing the diameter of the internal cylinder complete changes are 
produced in the configuration of the forces, and of the motions of the ions. All the 
other changes can also be tried in conjunction with this one. 
5. The material of the inner surface of the outer cylinder was also altered to note 
the influence upon the result of increased ionization at the metal surface. 
6. In trying to find the effect of any of these changes upon the observed velocity 
the greatest difficulty met with is due to the smallness of the effects, and their conse¬ 
quent masking by the irregularities of individual observations caused by the difficulty 
of maintaining a uniform radiation for a length of time sufficient to cover a number 
of readings. Individual observations taken under the same conditions may vary 
among themselves by a number of per cent., so a small change in the result cannot 
be detected unless a large number of observations is made. 
§ 6. Method of Conducting the Experiments. 
The following procedure was followed in taking readings with the apparatus. The 
Crookes’ tube and the lead slits were accurately adjusted, so that the beam of rays 
occupied the desired position, and the distance X of equation (9) was carefully 
measured. The cylinder AA' was connected to a chosen potential on the battery N. 
The electrometer quadrants, joined to the part B of the inner cylinder, were then 
disconnected from earth by means of the key Iv, and the zero reading was observed 
on the scale. The reading on the gasometer scale was also taken. At a definite 
time, observed on a chronometer, the valve at the gasometer was opened, so that the 
gas began to flow through the apparatus. After a short period, usually 10 seconds, 
sufficient to produce a steady state of flow in the apparatus, the primary of the 
induction coil was closed and the rays thus started. The rays were allowed to run 
for 30 seconds, and the primary of the coil was then broken, and the valve of the 
gasometer was also closed at a definite time. The electrometer reading was now 
taken, and the deflection produced was obtained. The key Iv was then closed, and 
the quadrants of the electrometer were connected to earth. From the reading on 
