Iv] . NATURE OF THE RADIATIONS 145 
appear always to go together and are present in the same pro- 
portion. The main facts known about the y rays are summarized 
below :— 
(1) Great penetratmg power. 
(2) Non-deviation in an intense magnetic field. 
(3) A law of absorption similar to that of cathode and £8 rays. 
(4) Occurrence of 8 and y rays together and in the same 
proportion. 
Three possible hypotheses may thus be considered :— 
(1) That the y rays are very penetrating Rontgen rays. 
(2) That they consist of negatively charged particles projected 
with a velocity very nearly equal to that of light. 
(3) That they consist of uncharged bodies projected with 
great velocity. 
Roéntgen rays are believed to be electromagnetic pulses set up 
by the sudden stoppage of the cathode rays produced in a vacuum 
tube. Thus it is to be expected that Roéntgen rays should be 
produced at the sudden starting as well as at the sudden stopping 
of electrons. Most of the @ particles from the radio-elements are 
projected with velocities much greater than those of the cathode 
rays Ina vacuum tube. Thus Réntgen rays of a very penetrating 
character should be set up, if the electron is very suddenly expelled 
with great velocity. This would account for the facts (1), (2) and 
(4), but it is at variance with (8) unless the relative conductivity 
of gases for a very penetrating type of X rays follows the law of 
conductivity of the @ or cathode rays’. Strutt has also pointed 
out that the proportion of y rays to 8 rays from radium is much 
greater than the proportion of X rays to the cathode rays produced 
in a vacuum tube. 
It has been shown that the @ rays from radium are complex 
1 (Added Feb. 18, 1904.) Mr A. S. Eve of M°Gill University, Montreal, has 
recently examined the relative conductivity of some gases for very ‘‘ hard” X rays 
after their passage through a lead screen 1-8 mms. thick, and has obtained ratios 
very different from those observed for ‘‘soft’”’ rays, but approximating closely to 
those obtained for the y rays. These observations remove the most serious objec- 
tion which has been urged against the view that the y rays are in reality X rays of 
a very penetrating type. 
R. B.-A. 10 
