a Rays from Radium and Polonium. 



511 



of pole-pieces and their positions as regards the length of the 

 path, as shown in the following table (two measurements are 

 given for position III. with different magnetic fields). In 

 the first three positions the main part of the field begins at 

 about the same place, but extends over lengths of the path 

 which are as 1 : 5 : 10 approximately. In position IV. we 

 have the same pole-pieces as in II., but displaced 4 cm. 

 further along the path of the rays from the slit. The value 

 of the field H at every point of the path of the rays was 

 determined by means of a small throw-bobbin and a ballistic 

 galvanometer in the usual way, and the value of §dx^Kdx 

 found graphically for use in the equation 



mv 



e 



= -j \dx \Kdx 



(see J. J. Thomson, ' Conduction of Electricity through 

 Grases,' p. 92), where d is the deflexion to either side of the 

 centre. 



II. 



Ill J 



IV. 



r- QJ 



**«="- 



2-Z 

 ^ p-. 



j 2-25 cm 



2-15 „ 



2-23 „ 

 223 „ 



6-15 „ 



tn 





O 

 •g bD 



a° 



i £ 



P H) 



Q3 O ■ 



p£ 



i of po 

 ured a 

 of ray 



ce froi 

 to cen 

 pieces. 



engtl 

 meas 

 path 



istan 

 slit 



pole- 



H? 



O 



0'80 cm. 



2*65 cm. 



3-75 „ 



4-03 „ 



7-SS „ 



617 „ 



7-88 „ 



617 ,. 



3-75 „ 



8-03 „ 



9 



q=l 





o i 



L c3 ^ ft. 



2.W 



c3 H 



4377 c.g.s. 119975 c.g.s. 



4618 



3082 

 3483 



4540 



240223 



245620 



280708 



170325 



a 





o 





M 





0/ 



T3 



q=l • 









nz; hs 



o a 



e_ cc 



CD 3 

 3 <o 









c3 « 



ff "3 



t> ° 





S w 



O ® 



§ I 



S3 





^ 





•41 cm. 



2-93 Xl0 5 



•80 „ 



3-00 „ 



•82 „ 



2-99 „ 



•92 „ 



305 „ 



•56 „ 



3-04 „ 



Mean value of — =3*00 x 10 5 c.g.s. electromagnetic units. 



The main error in the measurements comes in when 

 determining d, the deflexion ; for the bundle of a rays is 

 very heterogeneous in velocity, and under the action of the 

 magnetic field is spread out into a spectrum. The length of this 

 spectrum is of course determined up to a certain limit by the 

 length of exposure given, as it is strongest in the middle and 

 weak on both sides. The deflexion measured was to the 

 middle of the spectrum. An error of at least 3 per cent, is 



