MODERN VIEWS ON MATTER. 299 



perature of liquid air, and it is itself radio-active, but in such a way 

 that its power decays rapidly with time. Its radio-activity seems to 

 consist likewise in throwing away part of itself and leaving yet another 

 residue, likewise radio-active; and one of the residues so left seems 

 ultimately to pitch away electrons simply instead of atoms of matter. 

 It is not to be supposed that thorium and radium and uranium all 

 behave alike in details. The emanation of one may lose its activity 

 rapidly, and give rise to another substance which retains its power for 

 some time; the emanation of another element may last some time and 

 generate a substance whose activity rapidly decays; but into these 

 details it is not now the place to go. 



12. Assuming the truth of this strange string of laboratory facts, 

 we appear to be face to face with a phenomenon quite new in the his- 

 tory of the world. No one has hitherto observed the transition from 

 one form of matter to another: though throughout the Middle Ages 

 such a transmutation was looked for. The transmutation of elements 

 has been suspected in modern times on evidence vaguely deducible by 

 skilled observers from the spectroscopic details of solar and stellar 

 appearances. The evolution of matter has likewise been suspected by 

 a few chemists of genius: it was perceived, on the strength of Men- 

 delejeff 's law, that the elements form a kind of family or related series, 

 and it was surmised that possibly the barriers between one species and 

 the next were not absolutely infrangible, but that temporary transi- 

 tional forms might occur. All this was speculation ; but here in radio- 

 active matter the process appears to be going on before our eyes. Pro^ 

 fessor Eutherford and Mr. Soddy, who in Canada during the present 

 year have worked hard and admirably at the subject, have adduced 

 facts which point clearly in this direction; and they initially describe 

 what appear to be the first links of a chain of substances, all produced 

 in hopelessly minute quantities reckoned by ordinary tests, but which 

 yet by electrical means can easily be detected, and their boiling-points 

 and other properties investigated. Moreover, the investigators of these 

 strange substances are able to dissolve and precipitate, and perform 

 ordinary chemical operations on, these utterly imponderable and hope- 

 lessly minute deposits of radio-active substances, because of the power- 

 ful means of detection which their ionizing power puts into our hands 

 — even a few stray atoms being able by their ionizing power to dis- 

 charge an electroscope appreciably. 



13. Thus then it would appear that our theoretical conclusion con- 

 cerning the inevitable radiation and loss of energy from electrically 

 constituted atoms of matter, a loss which must involve them in neces- 

 sary change and dissolution, meets with quite unexpectedly rapid con- 

 firmation, and it is for that reason that I feel willing to accept tenta- 

 tively and as a working hypothesis this explanation of radio-activity. 



