202 THE RADIO-ACTIVITY OF MATTER. 



the. plate are al^le to traverse this same screen when it is interposed at 

 a point near their source. 



These experiments leave no douht as to the identity of the devial)le 

 rays with cathodic rays. However, it was necessary to prove that 

 they carry charges of negative electricity, and that they are deviated 

 by an electric field. 



M. and Mme. Curie, in a beautiful experiment, have shown that 

 the rays of radium charge negatively the bodies that receive them, 

 and that the source becomes charged positively. For this dou])lc 

 experiment it is necessary that all the conductors and the source itself 

 be completely enveloped in an insuliiting material, such as paraffin. 

 For the active body examined the charge was 4.10^^ C. G. S. units 

 per square centimeter of radiating surface per second. 



For my part, I have shown and measured the electrostatic deviation 

 l)y projecting the deviated shadow of a screen placed perpendicular to 

 the field, on a photographic plate. One of these apparatus is here 

 shown (fig. io), as well as one of the prints obtained (fig. 11), in which 

 on the two halves of the same plate ap})eiir the two deviated shadows 

 corresponding to the reversal of the electric field, of which the inten- 

 sity was 1.02 : 10^^ 



The l)allistic hypothesis attributes these phenomena to material 

 .masses transjjorting charges of negative electricity with very great 

 rapidity. Let /// be the material mass of a particle, e its charge, and 

 V its velocity. We know that in a magnetic field of aii intensity 

 //", the radius of curvature p of the circular trajectory is given ])y the 



equation ///:> = — v. The luunerical value of the product Ifp serves 



to siiow the charact(n- of each simi)le i-ay. On the other hand, in an 

 electric field of an intensity J\ the parameter of the parabolic traject- 

 ory is 1" ' The knowledge of th(\se two values gives — and v. 

 With a \alue of Up = 1,550 I obtained approximately ?' = 2.21x10'", 



and ' = L.4^XlO'. These figures ai-e entirelv of the same order in 



■in 

 value as those which led to the measurements made with cathodic rays, 



and the theoretical considerations with regard toZeeman's experiment. 



From the above figures we deduce that, from the fact of the deviable 

 radio activity under consideration, there escapes from each stjuare 

 centimeter of radio-active surface l.ti milligrams of matter in a thou- 

 .sand million years. 



By ext(Mi(ling thes(> m(>asuremeiits to radiations of difierent and 



well-known natuic^s, we ouuht to be al»l(> to determine if the relation — 



m 



is constant, or \ aiiable with one ray oi' another, and whetlier these do 

 not difler oidy in tlieir speeds; 1 have not yet finished the experiments 

 1 undertook to decide this fundamental question, but recent!}^ M. 



