Page:Radio-activity.djvu/150

 remarkable how nearly the velocity of the electron has to approach the velocity of light before the value of m/m_{0} becomes large. This

++-+-+ ++-+-+ ++-+-+
 * Value of|Observed value of|Percentage difference|
 * u/V |  m/m_{0}   |  from theoretical   |
 * |                |       values        |
 * Small |      1          |                     |
 * ·732  |      1·34       |       -1·5 %        |
 * ·752  |      1·37       |       -0·9 "        |
 * ·777  |      1·42       |       -0·6 "        |
 * ·801  |      1·47       |       +0·5 "        |
 * ·830  |      1·545      |       +0·5 "        |
 * ·860  |      1·65       |        0   "        |
 * ·883  |      1·73       |       +2·8 "        |
 * ·933  |      2·05       |       -7·8 " ?      |
 * ·949  |      2·145      |       -1·2 "        |
 * ·963  |      2·42       |       +0·4 "        |

is shown in the following table which gives the calculated values of m/m_{0} for different velocities of the electron.

Value of            u/V       small  ·1     ·5    ·9    ·99   ·999   ·9999     ·999999 Calculated value    m/m_{0}   1·00  1·015  1·12  1·81  3·28  4·96   6·68     10·1

Thus for velocities varying from 0 to 1/10 the velocity of light, the mass of the electron is practically constant. The increase of mass becomes appreciable at about half the velocity of light, and increases steadily as the velocity of light is approached. Theoretically the mass becomes infinite at the velocity of light, but even when the velocity of the electron only differs from that of light by one part in a million, its mass is only 10 times the value for slow speeds.

The above results are therefore in agreement with the view that the mass of the electron is altogether electrical in origin and can be explained purely by electricity in motion. The value of e/m_{0}, for slow speeds, deduced from the results was 1·84 × 10^7, which is in very close agreement with the value obtained by Simon for the cathode rays, viz. 1·86 × 10^7.