390 
tion 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 on- 
ward was the ascription of vibratory mo- 
tion to the atoms to explain heat. Then 
definite qualities were ascribed, definite 
mutual forces were called into play to ex- 
plain 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 propor- 
tions, and next to that we should put its 
success in explaining many of the prop- 
erties 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 representa- 
tion 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 con- 
sists of discrete particles with matter-free 
intervening spaces. 
Then Faraday’s discovery of the influ- 
ence 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 phe- 
nomena. The discovery that the velocity 
of electro-magnetic waves is the same as 
that of light waves is at least circumstan- 
tial evidence that the same medium trans- 
mits both. 
SCIENCE. 
[N. S. Vou. X. No. 247. 
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 hypothesis has not al- 
ways 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-centers sur- 
rounded by infinitely extending atmos- 
pheres of force as really an attempt to get 
rid of the dualism, and Faraday’s theory of 
point-centers 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 atoms 
are mere lociof a particular type of motion 
of this frictionless fluid. The sole differ- 
ences in the atoms are differences of posi- 
tion 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 en- 
ergy, MV’/2, is energy in and around the 
central whirls; our visible energy of posi- 
tion, 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 al] 
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 gar- 
ment of Nature, we resolve it in imagina- 
tion 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 consti- 
