‘TRANSACTIONS OF SECTION A. 619 
facts, inexplicable in that they are like nothing else. But imagine matter to con- 
sist of a crowd of separate particles with interspaces. Contraction and expansion 
are then merely a drawing in and a widening out of the crowd. Solution is merely 
the mingling of two crowds, and evaporation merely a dispersal from the outskirts. 
The most evident properties of matter are then similar to what may be observed 
in any public meeting. 
For ages the molecular hypothesis hardly went further than this. The first 
step onward was the ascription of vibratory motion to the atoms to explain heat. 
Then definite qualities were ascribed, definite mutual forces were called into play 
to explain elasticity and other properties or qualities of matter. But I imagine its 
first really great achievement was its success in explaining the law of combining 
proportions, and next to that we should put its success in explaining many of the 
properties of gases, 
While light was regarded as corpuscular—in fact molecular—and while direct 
action at a distance presented no difficulty, the molecular hypothesis served as the 
one foundation for the mechanical representation of phenomena. But when it was 
shown that infinitely the best account of the phenomena of light could be given 
on the supposition that it consisted of waves, something was needed, as Lord 
Salisbury has said, to wave, both in the interstellar and in the intermolecular 
spaces. So the hypothesis of an ether was developed, a necessary complement of 
that form of the molecular hypothesis in which matter consists of discrete particles 
with matter-free intervening spaces. 
Then Faraday’s discovery of the influence of the dielectric medium in electric 
actions led to the general abandonment of the idea of action at a distance, and the 
ether was called in to aid matter in the explanation of electric and magnetic 
phenomena. The discovery that the velocity of electro-magnetic waves is the same 
as that of light waves is at least circumstantial evidence that the same medium 
transmits both. 
I suppose we all hope that some time we shall succeed in attributing to this 
medium such further qualities that it will be able to enlarge its scope and take in 
the work of gravitation. 
The mechanical Cy nee has not always taken this dualistic form of material 
atoms and molecules, floating in a quite distinct ether. I think we may regard 
Boscovich’s theory of point-centres surrounded by infinitely extending atmospheres 
of force as really an attempt to get rid of the dualism, and Faraday’s theory of 
point-centres with radiating lines of force is only Boscovich’s theory in another 
form. But Lord Kelvin’s vortex-atom theory gives us a simplification more easily 
thought of. Here all space is filled with continuous fluid—shall we say a fluid 
ether ?—and the atomsare mere loci of a particular type of motion of this frictionless 
fluid. The sole differences in the atoms are differences of position and motion. 
Where there are whirls, we call the fluid matter ; where there are no whirls, we call 
it ether. All energy is energy of motion. Our visible kinetic energy, MV7/2, is 
energy in and round the central whirls; our visible energy of position, our potential 
energy, is energy of motion in the outlying regions. 
A similar simplification is given by Dr. Larmor’s hypothesis, in which, again, all 
space is filled with continuous substance all of one kind, but this time solid rather 
than fluid. The atoms are loci of strain instead of whirls, and the ether is that 
which is strained. ; 
So, as we watch the weaving of the garment of Nature, we resolve it in 
imagination into threads of ether spangled over with beads of matter. We look 
still closer, and the beads of matter vanish; they are mere knots and loops in the 
threads of ether. 
The question now faces us—How are we to regard these hypotheses as to the 
constitution of matter and the connecting ether? How are we to look upon the 
explanations they afford? Are we to put atoms and ether on an equal footing 
with the phenomena observed by our senses, as truths to be investigated for their 
own sake? Or are they mere tools in the search for truth, liable to be worn out or 
superseded ? 
That matter is grained in structure is hardly more than the expression of the 
