W. Crookes—Lines of Molecular Pressure. 225 
m 
cules, Prof. Stokes has pointed out that it would have to 
increase as the square of the velocity, in order that the deflec 
tion should be as great at high as at low velocities. 
Comparing the free molecules to cannon-balls, the magnetic 
pull to the earth’s gravitation, and the electrical excitation of 
the negative pole to the explosion of the powder in the gun, 
the trajectory will be flat when no gravitation acts, and curved 
when under the influence of gravitation. It is also much 
curved when the ball passes through a dense resisting medium ; 
it is less curved when the resisting medium gets rarer; and, as 
already shown, intensifying the induction spark, equivalent to 
increasing the charge of powder, gives greater initial velocity, 
and therefore flattens the trajectory. The parallelism is still 
closer if we compare the evolution of light seen when the shot 
strikes the target, with the phosphorescence on the glass screen 
from molecular impacts. 
