TRAVERSED BY CATHODE RAYS. 
0/ 
750 electrostatic units attached to the electrode B gained in 15 seconds a charge 
represented by 300 divisions on an arbitrary scale. A Bontgen ray focus tube 
giving out very strong rays was then used in place of that for producing the 
cathode rays, and was excited by an induction coil capable of giving a 50-centims. 
spark. Under these circumstances, with the same field, which was also in this case 
a saturating one, a capacity of 150 electrostatic units was charged in one minute to 
an amount represented by 20 on the same scale. This case, which is an extreme 
one, shows that the ionization by cathode rays was about 300 times that due to an 
intense Bontgen radiation. In the present investigation these latter rays, even if 
they did accompany the cathode rays, must have been very feeble, and could there¬ 
fore only exert an ionizing influence which may be left out of consideration. 
The known action of a magnetic field naturally suggested itself as a means of 
sifting out the cathode from any accompanying Bontgen rays. The intensity of the 
cathode rays, however, soon falls off owing to their rapid absorption by the air, and 
on this account it was necessary to place the chamber in which the ionization was 
measured close up to the discharge tube. Under these conditions it was found 
impossible to deflect the rays outside the tube without also deflecting those inside. 
This difficulty consequently rendered the test indecisive, and the method had to be 
abandoned. 
5. Discussion of Methods for Measuring the Ionizations 'produced in Different Gases. 
In the construction of Bontgen-ray bulbs, the disengagement of gas from the 
electrodes and the inside of the glass is facilitated by the application of heat to the 
tube. In the case of Lenard tubes, however, the joints are made of wax, and the 
final stage of exhaustion cannot be hastened by adopting this device. In practice a 
tube was kept attached to the mercury pump, and exhausted while the discharge 
was passing through it. After some hours of this procedure the coil was stopped, 
and the exhaustion was continued until only some traces of air were being taken 
over. On then exciting the tube, the vacuum was found to be sufficiently high for 
the cathode rays produced to penetrate the aluminium window. After running the 
cod for a short time, a small quantity of gas accumulated in the tube, and the 
pressure rose so high that the rays ceased to be propagated outside. After this air 
had been removed the vacuum again became good, and the original intensity of the 
rays was restored. As the ionizing power of the rays was very great, charges 
sufficiently large to be accurately measured were easily accumulated by exciting the 
tube only for short periods. By following this course quite satisfactory results 
were obtained and much loss of time was avoided. 
On account of this running down of the discharge tube, it was impossible, in 
comparing the ionizations in two different gases, to use an apparatus with a single 
chamber, such as that shown in fig. 1. In order to obtain accurate results, it was 
vol. cxcv.—A. 
i 
