ABSTRACT
The determination of the mass of the body, taken in conjunction with the experiments on the production of helium by the emanation, supports the view that the particle is in reality helium. The remarkable experiment of Sir William and Lady Huggins in which they found that the spectrum of the phosphorescent light of radium consisted of bright lines, some of which within the limit of error were coincident with the lines of helium in the ultra violet, strongly supports such a view. The consequence of the violent expulsion of the particle it is to be expected that it would be set into powerful vibration and give its characteristic spectrum. The radium emanation is the active principle of radium, which is the activity of radium is due to it. The very penetrating rays from it would light up an x ray screen brilliantly through a foot of solid iron.
