50 
Proceedings of Royal Society of Edinburgh. [sess. 
do, that there are hundreds of competent chemists who, when once 
the mechanical explanation of, at least, some of the principles of 
their science is pointed out to them, can almost at once, I have 
little doubt, follow these principles down into all their minute 
details, and give a mechanical explanation for each and every one 
of them. 
First, then, let me try to point out what I conceive to be the 
mechanical explanation of the radiation of heat. Let my readers 
conceive two of our bubble atoms to be brought so close together 
as to touch. If they were perfectly rigid, being perfect spheres, 
they could only touch at one point ; and all round that point for a 
certain distance (depending on the size of the spheres, the distance, 
of course, being greater for the large spheres and less for the small 
ones) would be included an area from which all ether would be 
excluded, because, within that area, the space separating the two 
spheres would be narrower than the diameter of an ethereal 
particle; and seeing that these particles are incompressible, they 
must all have been squeezed out by the act of bringing the spheres 
together. But we know that our spheres are not perfectly rigid — 
far from it ; some of them are very open-grained and squeezable ; 
therefore what must happen when they are brought so close to- 
gether as to touch 1 What happens to a boy’s “sucker ” when the 
air is excluded from between it and the flat stone to which he 
presses it ? Why, it simply sticks to the stone by the pressure of 
the air above it not being counterbalanced by an equal pressure in 
the opposite direction, all air being excluded from between it and 
the stone.* So with our sphere ; the ether being excluded 
from the area round the point of contact, that point would have 
momentarily to support the pressure which was formerly supported 
by all the points within the said area ; but that single point, not 
being able to support the pressure which was formerly distributed 
amongst all the points within the area, naturally would get 
squeezed inwards, the spheres being flattened at their point of 
contact, thus bringing more and more of their surfaces together, 
and squeezing, in the process, more and more of the ether out from 
* The spheres would begin to “ attract ” one another when they were some 
little distance apart (I use the word “attract” as having a well-established 
meaning) ; in fact, this process would begin when the film of ether between 
them became so thin as not to be able to carry the full pressure. 
