Page:Radio-active substances.djvu/51

mechanical bases upon the dynamical of little particles of matter charged in a state of motion.

These are the figures obtained by M. Kaufmann for ${\frac {e}{m}}$ and $v$.

$\scriptstyle {\frac {e}{m}}$			$\scriptstyle {v{\frac {\mathrm {c.m.} }{\mathrm {sec.} }}}$
Electro-magnetic units.
1	·865	$\times 10^{7}$	0	·7	$\times 10^{10}$		For cathode rays (Simoṅ).
1	·31	$\times 10^{7}$„	2	·36	$\times 10^{10}$„	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right\}\,}$	For radium rays (Kaufmann).
1	·17	$\times 10^{7}$„	2	·48	$\times 10^{10}$„
0	·97	$\times 10^{7}$„	2	·59	$\times 10^{10}$„
0	·77	$\times 10^{7}$„	2	·72	$\times 10^{10}$„
0	·63	$\times 10^{7}$„	2	·83	$\times 10^{10}$„

M. Kaufmann concludes, from comparison of his experiments with the theory, that the limiting value of the ratio ${\frac {e}{m}}$ for radium rays of relatively small velocity would be the same as the value ${\frac {e}{m}}$ for cathode rays.

The most complete experiments of M. Kaufmann were made with a minute quantity of pure radium chloride, with which we provided him.

According to M. Kaufmann's experiments, certain β-rays of radium possess a velocity very near to that of light. These rapid rays seem to possess great penetrating capacity towards matter.

 

Action of the Magnetic Field upon the α-Rays.

In a recent work, Mr. Rutherford announced that, in a powerful electric or magnetic field, the α-rays of radium are slightly deflected, in the manner of particles positively electrified and possessing great velocity. Mr. Rutherford concludes from his experiments that the velocity of the α-rays is of the order of magnitude $2\cdot 5\times 10^{9}\;{\frac {\mathrm {c.m.} }{\mathrm {sec.} }}$ and that the ratio ${\frac {e}{m}}$ for these rays is of the order of magnitude $6\times 10^{3}$, which is $10^{4}$ times as great as for the deflected β-rays. We shall see later that these conclusions of Mr. Rutherford are in agreement with the properties already known of the α-radiation, and that they account, in part at least, for the law of absorption of this radiation.

The experiments of Mr. Rutherford have been confirmed by M. Becquerel. M. Becquerel has further demonstrated that polonium rays behave in a magnetic field like the α-rays