424 Prof. Thomson, On the ionization of Gases, etc. 
to ionize the gas, for then the energy per unit will fall below the 
value required to ionize the gas. 
The coarseness of structure of light even of feeble intensity is 
probably almost as nothing in comparison with that of the 7 rays, 
for as we have seen the energy per unit in the 7 rays is probably 
10,000 times that in ordinary ultra-violet light. Thus the units 
in the 7 rays will, unless the intensity is exceedingly great, be 
very widely separated ; as these units possess momentum as well as 
energy they will have all the properties of material particles, 
except that they cannot move at any other speed than that of 
light. Thus we can readily understand why many of the pro- 
perties of the 7 rays resemble those of uncharged particles 
moving with high velocities. 
