i2 POPULAR SCIENCE MONTHLY. 



y rays of radium themselves carry a negative charge. The lead 

 envelope in his experiment acquired a positive charge in consequence 

 of the emission of a secondary radiation consisting of negatively 

 charged particles, projected with great velocity from the surface of 

 the lead. The electric charge acquired by the metal ring was due 

 to the absorption of these secondary rays by it, and the diminution 

 of this charge in a magnetic field was due to the ease with which these 

 secondary rays are deflected. It is thus to be expected that the en- 

 velope surrounding the radium, whether made of lead or other metal, 

 will always acquire a positive charge, provided the metal is not of 

 sufficient thickness to absorb all the y rays in their passage through it. 



No conclusive evidence has yet been brought forward to show that 

 the y rays can be deflected either in a magnetic or an electric field. In 

 this, as in other respects, the rays are very analogous to the Eontgen 

 rays. 



According to the theory of Stokes, J. J. Thomson and Weichert, 

 Eontgen rays are transverse pulses set up in the ether by the sudden 

 arrest of the motion of the cathode particles on striking an obstacle. 

 The more sudden the stoppage the shorter is the pulse, and the rays, 

 in consequence, have greater power of penetrating matter. In some 

 recent experiments Barkla found that the secondary rays set up by the 

 Eontgen rays, on striking an obstacle, vary in intensity with the 

 orientation of the vacuum tube, showing that the Eontgen rays exhibit 

 the property of one-sidedness or polarization. This is the only evi- 

 dence so far obtained in direct support of the wave nature of the 

 Eontgen rays. 



If Eontgen rays are not set up when the cathode particles are 

 stopped, conversely, it is to be expected that Eontgen rays will be set 

 up when they are suddenly expelled. Now this effect is not observable 

 in an X-ray tube, since the cathode particles acquire most of their 

 velocity, not at the cathode itself, but in passing through the electric 

 field between the cathode and anticathode. It isy however, to be 

 expected theoretically that a type of Eontgen rays should be set up at 

 the sudden expulsion of the /? particles from the radio atoms. The 

 rays, too, should be of a very penetrating kind, since not only are the 

 charged particles projected with a speed approaching that of light, but 

 the change of motion must occur in a distance comparable with the 

 diameter of an atom. 



On this view the y rays are a very penetrating type of Eontgen 

 rays, having their origin at the moment of the expulsion of the /? 

 particle from the atom. Tf the /? particle is the parent of the y rays 

 the intensity of the /? and y rays should, under all conditions, be pro- 

 portional to one another. I have found this to be the case, for the 

 7 rays always accompany the /3 rays and, in whatever way the /? ray 



