1901 - 2 .] Mr J. Fraser on Constitution of Matter and Ether. 39 
quantities of ether upon which the motion was impressed. The 
expansion would continue until all the particles worked their way 
out to the surface by centrifugal tendency, and afterwards would 
still continue to expand until this tendency and the pressure of the 
ether exactly balanced one another.* 
I said they would work their way out to the surface of the 
bubble because of the greater centrifugal tendency of the inner 
particles, owing to their narrower orbits in that position, and which 
orbits at the surface would, of course, be equalised. In this way 
bubbles of various sizes and degrees of consistency might be 
formed. For instance, a bubble — or atom, as I shall call it after 
this — might consist of 16 or any other number of times the number 
of units as another, and yet not have a greater surface area than 
the latter, the constituents of the atom of least mass in proportion 
to size having a correspondingly greater motion. Their motions 
must be so rapid as to preclude the possibility of any of the 
particles of the medium ever penetrating the surfaces of the atoms. 
To illustrate the possibility of this, suppose a stone to be thrown 
at a wheel in very rapid rotation, the stone could not penetrate 
between the spokes if the velocity of the wheel were great enough, 
for, before the stone could penetrate more than a small distance, 
some one or other of the spokes would be certain to intercept it. 
The particles must move rapidly enough to cover the space 
between them over and over again, in every direction normal to 
the surface of the atom, and to be, as it were, everywhere at once, 
in order to prevent penetration. That this motion must be far 
greater than the motion of the in-pressing particles of the medium 
may be realised by referring to the speed of a planet round the sun, 
as compared with the distance it would fall towards him in the 
* It will, no doubt, be observed that this is a position of unstable equili- 
brium, which the slightest disturbance would overthrow. How, then, are we 
to save the situation ? It is saved already. For, as pointed out above, the 
particles would be more bombarded on their fronts than on their rears, so 
that although, by falling in towards the centre, they would regain their former 
speed, their orbits, if ever they were circular, would never be so again, but 
always elliptical, and no bubble could ever be in so expanded a state as it 
would be possible for it to be if this excess of bombardment on the fronts of 
the particles over the rears did not exist. In short, owing to this excess of 
bombardment on their fronts, no bubble could ever expand to the stage of 
unstable equilibrium. 
