1901 - 2 .] Mr J. Fraser on Constitution of Matter and Ether. 37 
direction, in great circles, all round the bubble, to preserve it 
unbroken to all eternity, or so long as the pressure lasted. 
Now, the first thought to strike one on conceiving an idea of 
this kind is, how is it possible for motion to be conserved under the 
above circumstances 1 And to answer this satisfactorily, one 
must disabuse one’s mind of the idea of ordinary ponderable bodies 
being engaged in the operation. The bodies engaged are ideal 
ones — none the less real for all that — ideally smooth, ideally 
globular, and infinitely hard or rigid, so that motion can be 
transferred from one to another instantaneously without any loss, 
which is the same as saying that they are perfectly elastic. 
Another thing which must not be forgotten is, that they move 
in pure empty space ; for they only come into contact with the 
particles of the medium at their outer surfaces, and these are per- 
fectly smooth, and those contacts are only momentary, for the 
particles of the medium can never be at rest, but are incessantly 
bombarding the revolving particles in a direction at right angles 
to their orbits, just as the planets are acted upon by the sun’s 
gravity. 
But an objection will arise — and perhaps this is the best place 
to deal with it — that, owing to the composition of the velocities of 
the bombarding and revolving particles, or the particles of the 
medium and of the bubble, the revolving particles would sustain 
more impingements on their fronts than on their rears — that is, 
that the impingements of the particles of the medium on those 
of the bubble would, instead of being strictly at right angles, be 
directed more on the front, and thus motion would be lost. This 
objection, if it could be sustained, would, apparently at least, 
prove fatal to the theory. But, happily, it cannot be sustained, as 
I shall show. It is a well known fact to astronomers, that should a 
planet moving in a circular or other orbit meet with any obstruc- 
tion to its motion, that the obstruction, instead of slowing down 
the motion, would ultimately hasten it ; and that after being in 
perihelion, it would return to that part of its orbit where it was 
obstructed, to go through the same course again if it were no 
further obstructed, but if it were, each return to the perihelion 
after obstruction would be at shorter and shorter intervals, and a 
less and less distance from the sun, till at last it would graze his 
