348 RADIO-ACTIVE PROCESSES 

The removal of an electron from the atom does not appear to 
permanently affect the stability of the system, for no evidence has 
so far been obtained to show that the passage of an intense electric 
discharge through a gas results in a permanent alteration of the 
structure of the atom. On the other hand, in the case of the 
radio-active bodies, a positively charged particle of mass about 
twice that of the hydrogen atom escapes from the heavy radio- 
atom. This appears to result at once in a permanent alteration of 
the atom, and causes a marked change in its physical and chemical 
properties. In addition there is no evidence that the process is 
reversible. 
The only direct experimental evidence of the transformation 
of matter has been derived from a study of the radio-active 
bodies. If the disintegration theory, advanced to account for the 
phenomena of radio-activity, 1s correct in the main essentials, then 
the radio-elements are undergoing a spontaneous and continu- 
ous process of transformation into other and different kinds of 
matter. The rate of transformation is slow in uranium and thorium, 
but is fairly rapid in radium. It has been shown that the fraction 
of a mass of radium which is transformed per year hes between 
1/2000 and 1/10000 of the total amount present. In the case of 
uranium and thorium probably a million years would be required 
to produce a similar amount of change. The process of trans- 
formation in uranium and thorium is thus far too slow to be 
detected within a reasonable time by the use of the balance or 
spectroscope, but the radiations which accompany the transforma- 
tion can readily be detected. Although the process of change is 
slow it is continuous, and in the course of ages the uranium and 
thorium present in the earth must be transformed into other and 
simpler types of matter. 
Those who have considered the possibility of atoms undergoing 
a process of transformation, have generally thought that the 
matter as a whole would undergo a progressive change, with a 
gradual alteration of physical and chemical properties of the whole 
mass of substance. On the theory of disintegration this is not the 
case. Only a minute fraction of the matter present breaks up in 
unit time, and in each of the succession of stages through which 
the disintegrated atoms pass, there is in most cases a marked 
