MODERN VIEWS ON MATTER. 223 



a sort of X rav.s or ether pulses; and was sii])se([uently assiuned to eon- 

 sist ehieflv in the bodily emission of ch^ctrons, which were sliot oti' 

 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 lig-ht 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, l)ut 

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

 as secondar}' or subsidiary results of the main phenomenon. 



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

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

 ruary this very 3"ear, to consist in the flinging- nwny with g-reat violence 

 of actual atoms of matter — atoms electrihed 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 positiveh" charged and possessed 

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

 bard to an extj-aordinary 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 

 bombardment from a radio-active substance continues without inter- 

 mission and apparenth' Avithout sign of diminution or cessation. There 

 is ever}^ reason to believe that a minute scrap of radium, scarcely per- 

 ceptible to the eye. may go on emitting these energetic projectiles for 

 hundreds of years. 



11. At first sight the fact that it is merely atoms of matter which 

 are being flung ofl' b^' most radio-active substances, and that ethereal 

 and other efi'ects are subsidiarv to this emission of substance, seems 

 to lessen the interest attaching to the phenomenon, reducing it to 

 something of merely chemical importance and suggesting a resem- 

 blan(;e to scent or other volatilization from solid bodies. But Professor 

 Rutherford, with great skill, succeeded in determining appi'oximatel}^ 

 the atomic weight of the uttiM-ly imperceptible amount of substance 

 thrown ofl', as well as its speed, and found that it was not l)y ai'.y in<>ans 

 the radio-active substance itself which was evaporating, l)ut something 

 quite difl'erent. 



Plainly, if an elementary form of matter is found to ])e throwing 

 ofl' anothiM' substance, it becomes inqDcrative to iii(|uire what that sub- 

 stance is and what it is that is left l)ehind. Now, tlu^ atomic weight of 

 radium, or of thcn-ium or uranium, or of anv known stronglv radio- 



