1907.] on Rays of Positive Electricity. 587 



cated in Fig. -4, the two bands being produced by carriers having 



different maximum values of — . The greatest value of — obtained 



m m 



with hydrogen was the same as in air, 1*2 x 10"^, the velocity was 



1 • 8 X IC^ cm. per sec. The presence of the second band indicates 



that mixed with these we have another set of carriers, for which the 



maximum value — is half that in the other band, i.e. 5 x 10^. The 

 m 



curvature of the boundary generally observed is due to the admixture 



of these two rays. 



Positive Rays in Helium. 



In helium the phosphorescence is bright, and the deflected patch 

 has in general the curved outline observed in hydrogen. I was fortu- 

 nate enough, however, to find a stage in which the deflected patch 

 was spHt up into two distinct bands, as shown in Fig. 9. The maxi- 

 mum value of — in the band a was 1 '2 x 10^, the same as 

 m 



in air and hydrogen, and the velocity was 1*8 x 10*^; while 



the maximum value of — in band b was almost exactly one t>^ 

 m 



quarter of that in a (i.e. 2*9 x 10^). As the atomic weight 



of helium is four times that of hydrogen, this result indicates 



that the carriers which produce the band h are atoms of Fig. 9. 



helium. This result is interesting because it is the only case 



(apart from hydrogen) in which I have found values of corre- 



sponding to the atomic weight of the gas ; and even in the case of 

 helium, when the pressure in the discharge-tube is very low and the 



electric field very intense, the characteristic rays with — = 2*9 x 10^ 

 sometimes disappear, and, as in all the gases I have tried, we get two 



sets of rays, for one set of which — = 10^ and for the other 5 x 10^. 



m 



Although the helium had been carefully purified from hydrogen, 

 the band a (for which - = 10^) was generally the brighter of the 



two. The case of helium is an interesting one ; for the class of posi- 

 tive rays, known as the a rays, which are given off by radioactive sub- 

 stances, would a jyriori seem to consist most probably of helium, since 

 helium is one of the products of disintegration of these substances. 



The value of — for these substances is 5 x 10^, where we have seen 



??^ 



that in helium it is possible to obtain rays for which — =2*9 x 



