MODERN VIEWS ON MATTER. 297 



of the constituents of an atom seemed to constitute a difficulty, for it 

 suggested that an atom of matter was not really a permanent and 

 eternal thing, but that it contained within itself the seeds of its own 

 decay and ultimate dissipation into the separate electrons of which 

 it was composed. The process might indeed be exceedingly slow, the 

 radiation loss might be almost imperceptible, but, in so far as an 

 atom is composed of revolving electrons, it is inevitable that radiation 

 of energy must go on from it, and that this must in the long run have 

 some perceptible degenerative result. 



10. That result has quite recently, I believe, been experimentally 

 discovered, and is a part of the phenomenon known as 'radio-activity.' 



So now we come to the most remarkable and probably the most 

 interesting step of all. 



The phenomenon of spontaneous radio-activity, discovered first by 

 Becquerel in uranium and thorium, and greatly extended by the bril- 

 liant chemical researches of M. and Mme. Curie which resulted in the 

 discovery of radium (they are coming to London next week, and will 

 be received, I expect, royally by the scientific world), was at first sup- 

 posed to consist in the emission of a sort of X-rays or ether pulses; 

 and was subsequently assumed to consist chiefly in the bodily emission 

 of electrons, which were shot off from the radio-active substance as 

 they are from a negative electrode in a vacuum-tube, or as they are 

 in air when ultra-violet light falls upon clean negatively charged 

 surfaces. 



As a matter of fact both these modes of radiation — the wave form 

 and the corpuscular form — are emitted by radio-active bodies, but 

 they turn out to be of subordinate importance, and must be regarded 

 as secondary or subsidiary results of the main phenomenon. 



The main fact of radio-activity has been shown by Professor 

 Eutherford, of Montreal, in a paper published in the month of Feb- 

 ruary this very year, to consist in the flinging away with great violence 

 of actual atoms of matter: atoms electrified indeed, but not negatively 

 like electrons, and not small or penetrating like them, but full-sized 

 atoms, such as are easily stopped by a thin sheet of metal, or even 

 by a sheet of paper — atoms which are positively charged and possessed 

 of a remarkable amount of energy, ionizing the air which they bom- 

 bard to an extraordinary extent, and likewise generating quite a per- 

 ceptible amount of heat wherever they strike; producing indeed a flash 

 when they strike a suitable target, as Crookes has shown, quite like 

 the impact of a cannon-ball on an armor-plate. Their speed, indeed, 

 far exceeds that of any cannon-ball that ever existed, being as much 

 faster than a cannon-ball as that is faster than a snail's crawl; a 

 hundred times faster than the fastest flying star, these atomic pro- 

 jectiles constitute the fastest moving matter known. This furious 



