AN EXPERIMENTAL STUDY OF RADIO-ACTIVE SUBSTANCES. 161 



capable of beinjr a)).sorl)cd by certain elements of hit^h atomic weight, 

 such as uranium and thorium. 



Becquerel, reflecting- on the marvelous spontaneous emission of 

 light, remarked: If it can be pi-oved that the luminosity causes no loss 

 of energy, the state of the uranium is like that of a magnet which has 

 been produced by an expenditure of energy and retains it indefinitel}^, 

 maintaining around it a field in which transformation of energy can be 

 efi^ected; but the photographic reductions and the excitation of phos- 

 phorescence in a sensitive screen require an expenditure of energ}^, of 

 which the sourc-e can only be in the radio-active substances. As this 

 expenditure is slight, perhaps the bodies have a large reserve of 

 energy which can be drawn upon for years without showing loss. At 

 any rate, it has been impossible, says Becquerel, to bring about any 

 appreciable variation in the intensit}^ of the emission by physical 

 influences. 



Somewhat later, Becquerel hazarded the opinion that the radiation 

 of radium is composed, at least in part, of cathodic rays; but these 

 have been proved to be material, hence the induced activity must be 

 caused by material particles impinging upon the substances excited. 

 This materialistic theory seems to be confirmed ])y the results of 

 ingenious experiments made by Madame and Monsieur Curie. They 

 placed a sensitive plate beneath a salt of radium, supported upon a slab 

 of lead, in the vicinity of an electro-magnet. Under these conditions 

 when the current was passing the rays emitted by the chemical salt 

 were bent in curved lines upon the sensitive plate, making impressions. 



It ma}^ be objected, says a French writer in the Revue generale 

 des Sciences, that this theory requires us to admit actual loss of par- 

 ticles of matter, nevertheless the charges are so feeble that the most 

 intense radiation 3"et observed would require millions of years for the 

 removal of one milligram of substance. 



The same writer raises the question, Which of the observed phe- 

 nomena is the primary one — does the radiation of radium excite cathodic 

 rays, or do the latter exist in the chemical compounds ? And he regards 

 the latter as improbable. The primordial source of energy in radium 

 probably resides, he adds, in the ultra-violet light, and the efflux of 

 material particles that ensues is only a secondary phenomenon, but on 

 a far larger scale than has previously been observed. 



Speculations as to the future history and applications of these won- 

 der-working bodies press upon even the dullest imagination. If a few 

 grams of earth-born material, containing probably onW a small per- 

 centage of the active body, emit light enough to affect the human eye 

 and a photographic plate, as well as ra3's that penetrate with X-ray 

 power, what degree of luminosity, of actinism, and of Rontgenism is 

 to be expected from an hundredweight of the quintessence of energy 

 purified from interfering matter? 

 SM 99 11 



