194 
MB. J. ZELENY ON THE VELOCITY OF THE IONS 
undertaken, partly because of advances in our understanding of some of the intrica¬ 
cies of the conduction, and partly because it seemed desirable that a satisfactory 
direct method be devised whereby the velocities of the two ions could be determined 
separately, and in which the experimental conditions could be subjected to a number 
of variations sufficient to ensure freedom from serious errors. 
In undertaking this, an attempt was first made to use a modification of the method 
employed by the writer in the determination of the ratio of the two ionic velocities, 
which is described in a previous paper. The ions were made to go against a stream 
of gas in a tube by means of an electric field, and their velocity was compared to that 
of the gas stream. The jiresence of the gauzes necessary for the production of the 
electric field was found, however, to disturb the gas stream sufficiently to produce a 
turbulent motion in it and so prevented the attainment of absolute results. 
The method which was then developed, and the one with which all of the results of 
this paper were obtained, also consisted in directly comparing the ionic velocity with 
that of a stream of gas, but avoided the difficulty of the above by having the electric 
field at right angles to the gas stream. 
§ 2. The Method Used for Determining the Velocity. 
A stream of gas is passed between two concentric cylinders which are kept at 
different potentials, and which at one place are traversed by a beam of Rontgen rays. 
The ions which are produced between the two cylinders by the rays are carried 
along by the stream of gas and at the same time, under the influence of the electric 
force, they move at right angles to the axis of the tubes. The resultant paths of the 
ions are inclined by an amount depending upon the relative value of the velocity of 
the gas stream to that of the ions. 
Let CC' in fig. 1 represent a section of a portion of the outer cylinder, and DB 
that of the inner one, and let del represent a narrow beam of rays traversing the two 
cylinders at right angles to their common axis. When the two cylinders are at 
C d 
Fig. 1. 
