Velocities of a Particles from Radioactive Substances. 5(57 



slides of the originals by contact, and then projecting the 

 slides on to " gaslight ; ' paper by the lantern. It is easy to 

 see from the photographs that the inside edges of the bands 

 are very sharp and almost ideal for purposes of measure- 

 ment ; all our measurements were made between the inside 

 edges of the different pairs of bands, the normal deflexions 

 being then calculated from these measurements by the aid 

 of the theory of which the principle has been indicated above. 



Since the magnetic deflexions of the a. rays were deter- 

 mined with the same a-ray tube as was used in the electro- 

 static case, similar corrections are necessary to deduce the 

 true deflexion due to the central rays. The same general 

 theory is applicable with the exception that the quantity 

 under the brackets (equation 1) is raised to the power 1/3 

 instead of 2/3. The reason of this is obvious, since the de- 

 flexion of rays in the magnetic field is inversely proportional 

 to the first power of the velocity instead of the second power 

 as in the electrostatic case. The photographic bands obtained 

 with a magnetic field have sharply defined inside edges, and 

 the bands due to radium are narrower than the geometrical 

 image. 



The explanation is similar to that given in the electro- 

 static case. The results of three distinct series of measure- 



ments of the values of -^- and ^ not only for the a rays 



from radium C, but from radium A and the emanation are 

 given below. The experiments 2 and 3 were made with the 

 same a-ray tube, but with different voltages. 



Table of Results. 



In electrostrostatic experiments : applied voltages 



(1) 1950. (2) .1435. (3) 1958. 



Plate. 



RaC. 



1)1 V 



E " 



m v 



Expt. 1 : with 



tube 1*85 cm. 



stopping power. 



Expt. 2 : with 



tube 200 cm. 



stopping power. 



Expt. 3 : with 



tube 200 cm. 



stopping power. 



3 605! 6 269! 4824 

 xlO* xl0 u xl0' } 



3-555 



xlO* 



6033, 4813 

 X10 14 ; xlO 3 



3-555 6100 i 4-826 

 XlO*' XlO 11 1 XlO 3 



Ra A. 



1 



v i 



E. 



m '< 





Ra Em 





mv 

 E 



mv~ 



VI V 



E* 



viv- 

 E ' 



E 



m 



4-822 

 XlO 3 



— 



- ! 



— 



- 



2041 

 XlO"' 



4-174 

 XLO* 4 



4-824 ' 



2-717 

 XlO 5 



3-560 

 XlO 14 



2941 

 XlO" 1 



4-185 

 X 10 u 



4 837 

 XlO 3 



2-717 

 XlO 5 



3-563 

 X10 :4 



4826 

 XlO 3 



