ABSTRACT
The change in refractive index results from chemical changes in the composition of the glass due to the action of the α rays. The range of the a particles in mica thus agreed closely with the observed radius of the halo. The evidence seems conclusive that these halos are of radioactive origin. Recently, in the course of some experiments with the radium emanation, had occasion to allow a large quantity of purified emanation to decay in a fine capillary tube of soda glass. The capillary was placed under a microscope to examine whether any indication of the effect of the α rays from the emanation and its products in the glass could be observed. The distance from the edge of the capillary bore to the edge of the altered area was equal in all parts of the tube, notwithstanding wide variations in the bore of the capillary along its length.
