UNSUSPECTED RADIATIONS. 381 



for move than one-hundredth part of a second to begin to glow, and 

 long- aftei- the glow has disappeared the}^ continue to send out the 

 invisible radiations affecting the photographic film for months, and 

 even years, as it appeared later on, even though the salt of the metal 

 remained all the time in a closed box locked in a drawer in a dark 

 room. The Becquerel radiations are thus quite different from phos- 

 phorescence or fiuorescence. They are similar in nature to the kathode 

 ra^^s and the K<)ntgen rays, with one substantial ditierence only. In 

 the vacuum tul)e we know the force — electricity — which supplies the 

 energy for setting the atoms or the molecules of the gas into motion, 

 while here we see no such source of energy; the radiations continue 

 months and years after the phosphorescent body has seen the light, 

 and ther(^ is no notal)le diminution of its radiating activity. Besides, 

 certain sub.stances need not he influenced l)y light at all for sending 

 out I'adiations, and this properly l)elongs, as it appeared later on, not 

 Old}' to phosphorescent bodies, but to a great variety of substances, 

 organic and inorganic, so that one has to ask oneself whether the 

 B(»C(|uerel radiations are not a property of matter altogether. 



The first experiments of Becquerel were these: A little lamina of the 

 dou])Ie sulphide of uranium and potassium, which has a great phos- 

 phoi-escing power, was placed upon a black paper envelope containing 

 a photographic film. A glass plate, or a thin plate of aluminum or of 

 copper, was introduced between the two, and the whole was either 

 exposed to diffused daylight or closed in a black box and put in a 

 drawer. In a short time in the first case — in a few hours in the sec- 

 ond — the photographic film would show that some rays had been radi- 

 ated from the sulphide. They had traversed the paper and partly also 

 the metals, though less so than the paper, and the plate bore the image 

 or the shadow of the piece of copper. 



The analogy with the Rontgen rays was thus evident, and further 

 incjuiry confirmed it. Like the kathode rays, the Becquerel radiations 

 are deflected from their rectilinear paths by a magnet; but, like the 

 Rontgen rays, they can not be reflected or broken or polarized.' And, 

 like the kathode rays, they render the air through which they pass a 

 conductor of electricity; they carry electricity with them, and con- 

 sequently it is most probable that they are not vibrations of the ether, 

 but electrified particles of matter, or ions, like the kathode rays. And 

 so we have the puzzle, or, at least, the quite unexpected fact, of matter 

 radiating molecules without any electrical or luminous or heating cause 

 provoking and maintaining that radiation or evaporation. 



The Becquerel rays, as was just said, send electrified particles 

 which are capable of neutralizing the electrici ty of other bodies with 



'In his first researches Becquerel thought that he had seen reflection and refrac- 

 tion of these rays; but now he has abandoned this idea (Comptes Eendus, 1899, \ ol. 

 CXXVIII, p. 771). 



