the rays. The difference in velocity between the rays is in consequence not as great as this calculation would indicate. On examination of the rays from uranium, Becquerel found that the radiation is not as complex as that from radium, but consists wholly of rays for which the value of HR is about 2000.
78. Examination of the β rays by the electric method. The presence of easily deviable rays given off from an active substance can most readily be shown by the photographic method, but it is necessary, in addition, to show that the penetrating rays which produce the ionization in the gas are the same as those which cause the photographic action. This can be conveniently tested in an arrangement similar to that shown in Fig. 25.
The radio-active matter A is placed on a lead block B´´ between the two parallel lead plates BB´. The rays pass between the parallel plates and ionize the gas between the plates PP´ of the testing vessel. The magnetic field is applied at right angles to the plane of the paper. The dotted rectangle EEEE represents the position of the pole piece. If a compound of radium or thorium is under investigation, a stream of air is required