RADIUM. 



189 



Fig. 1.— CouduL-tivity of air augmented by 

 radium. 



Under certain conditions the radiations of radium facilitate the pas- 

 sage of sparks between two conductors placed in air. This is illus- 

 trated by the apparatus shown in tig. 1, consisting of an induction 

 coil, B, from the poles, P and P', of which two metallic circuits are 

 led to micrometric sparking devices, M and M', at considerable dis- 

 tance apart, and offering two distinct paths of equal resistance to the 

 passage of sparks. The micrometers 

 are adjusted so that each transmits 

 equally an al)undance of sparks be- 

 tween their terminals. Upon bring- 

 ing a fragment of radium near one of 

 the micrometers the sparks cease to 

 pass at the other. 



It appears to be the most penetra- 

 ting rays which are most eti'ective in promoting electrical conductivity, 

 for the efficiency of the rays for this purpose is not greatly reduced 

 b}^ interposing a lead screen 2 centimeters thick, although the larger 

 portion of the rays is arrested ])y such a screen. 



IV. 



The radiations of radium can be neither reflected nor refracted. 

 They form a heterogeneous mixture, separable into three groups, 

 which follosving the nomenclature of Rutherford we will designate by 

 the Greek letters a^ /i, and y. These groups may be discriminated 



hy the aid of the magnetic 

 tield; for in an intense mag- 

 netic field the a rays are 

 slightly deviated from a 

 ivctilinear course in the 

 same manner as the "canal 

 rays" in vacuum tubes, 

 while the /i^ rays are devi- 

 ated like the cathode rays, 

 and the y rays, like those 

 of R(>ntgen, are not devi- 

 ated at all." 



A l)it of radium (R, fig. 



2) is placed within a small 



i cavity in a block ol^ lead. 



viu. -.-.Magnetic separation of a, fi, and y rays. J ,^ ^\^^, absence of all mag- 



netic action the radiation escapes from the l)l()ck as a rectilinear pen- 

 cil, but in a uniform magnetic field normal to the plane of the ligure, 



«Giesel, Wicd. Ann., November 2, 1899. Meyer and Von Schweidler, ,\kad. 

 Anzeig. Wien, November ;^ and 9, 1899. Beniuerel, C. R., December 11, 1899, Jan- 

 uary 26 and February 16, 19C«. P. Curie, C. R., January 8, 1900. Villard, C. R., 

 Vol. (!XXX, I). 1010. Uiitberford. I'hysik-Zeitseli., January 1.'), 1903. 



