i 
acl i eae 
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Feb, 1, 1883] 
NATURE 
329 
as it is split up by dissociation ; and, instead of each nascent 
radicle or atom taking with it neutral ether, one takes a certain 
definite quantity of positive, the other the same amount of 
negative, electricity. In the liquid state the atoms are capable of 
locomotion; and a continuous shearing force applied to the 
ether in such liquids causes a continual procession of the matter 
and associated electricity, the positive one way, and the negative 
the other, and thus all the phenomena of electrolysis.. 
What I say about electricity, however, is not to be taken 
without salt, you will not regard it as recognised truth, but as a 
tentative belief of your lecturer’s which may be found to be 
more or less, and possibly more rather than les:, out of accord- 
ance with facts. I can only say that it hangs phenomena to- 
gether, and that it has been forced upon my belief in various 
ways. 
Now what about the free ether of space, is it a conductor of 
electricity? There are certain facts which suggest that it is, and 
Edlund has suggested that it is an almost perfect conductor, 
When a sun-spot or other disturbance breaks out on the sun, 
accompanied as it is, no doubt, by violent electric storms, the 
electric condition of the earth is affected, and we have aurorz 
and magnetic disturbances. Is this by induction through space? 
or can it be due to conduction and the arrival of some micro- 
scopic portion of a derived current travelling our way ? 
For my part I cannot think the ether a conductor. Maxwell 
has shown that conductors must be opaque, and ether is 
nothing if not transparent; one is driven, then, to conclude that 
what we call conduction does not go on except in the presence 
of ordinary matter—in other words, perhaps, that it is a pheno- 
mena more connected with bound ether than with free. 
But now, looking back to Fresnel’s hypothesis of the extra 
density of the ether inside gross matter, and also to the fact that 
it must be regarded as incompressible, the question naturally 
arises how can it be densified by matter or anything else? 
Perhaps it is not; perhaps matter only strains the ether towards 
itself, thus slackening its tension, as it were, inside bodies, not pro- 
ducing any real increase of density ; and this is roughly McCullagh’s 
form of the undulatory theory. In this form gravitation may be 
held to be partially explained ; for two bodies straining at the 
ether in this way will tend to pull themselves together. In fact 
Newton himself pointed out that gravitation could be produced 
if only matter exerted this kind of strain on all pervading ether, 
the tension varying as the inverse distance. 
He did not follow the idea up, however, because he had then no 
other facts to confirm him in his impression of the existence of 
such an ethe , or to inform him concerning its properties. We 
now not only feel sure that an ether exists, but we know some- 
thing of its properties ; and we also have learnt from light and 
from electricity, that some such action between matter and ether 
actually occurs, though how or why it occurs we do not yet 
know. Iamtherefore compelled to believe that this is certainly 
the direction in which an ultimate explanation of gravitation and 
of cohesion is to be looked for. 
In thinking over the Fresnel and McCullagh forms of the 
undulatory theory, with a view to the reconciliation between 
them which appears necessary and imminent, one naturally asks, 
is there any such clear distinction to be drawn between ether 
and matter as we have hitherto tacitly assumed? may they not 
be different modifications, or even manifestations, of the same 
thing? 
Again, when we speak of atoms vibrating, how can they 
vibrate ? of what are their parts composed ? 
And now we come to one of the most remarkable and sug- 
gestive speculations of modern times—a speculation based on this 
experimental fact, that the elasticity of a solid may be accounted 
for by the motion of a fluid ; that a fluid in motion may possess 
rigidity. 
I said that rigidity was precisely what no fluid possessed ; at 
rest this is true; in motion it is not true. 
Consider a perfectly flexible india-rubber O-shaped tube full 
of water ; nothing is more flaccid and limp. But set the water 
rapidly circulating, and it becomes at once stiff; it will stand on 
end for a time without support; kinks in it take force to make, 
and are more or less permanent. A practicable form of this 
experiment is the well-known one of a flexible chain over a 
pulley, which becomes stiff as soon as it is set in rapid motion, 
This is called a vortex filament, and a vortex is a thing built 
up of a number of such filaments. If they are arranged parallel 
to one another about a straight axis or core, we have a vortex 
cylinder such as is easily produced by stirring a vessel of water, 
or by pulling the plug out of a wash-hand basin ; or such as are 
made in the air on a large scale in America, and telegraphed 
over here, when they are called ‘‘ cyclones,” or ‘ depressions.” 
The depression is visible enough in the middle of revolving water. 
These vortices are wonderfully permanent things, and last a long 
tme, though they sometimes break up unexpectedly. 
Vortices need not have straight cores, though they may have 
cores of various ring forms, the simplest being a circle. ‘To 
make a vortex ring, we must take a plane disk of the fluid, and 
ata certain instant give to every atom in the disk a ‘certain 
velocity forward, graduating the velocity according to its dis- 
tance from the edze of the disk. We kave as yet no means of 
doing this in a frictionless fluid, bnt with a fluid such as 
air and water it happens to be easy ; we have only to knock a 
little of the fluid suddenly out of a box through a sharp-edged 
hole, and the friction of the edges of the hole does what we 
want. The central portion travels rapidly forward, and returns 
round outside the core, rolling back towards the hole. But the 
impetus sends the whole forward, and none really returns ; it 
rolls on its outer circumference as a wheel rolls along a road. In 
a perfect fluid it need not so roll forward, as there would be no 
friction, but in air or water a vortex-ring has always a definite 
forward velocity, just as a locomotive driving-wheel has when it 
does not slip on the rails. 
We have in these rings a real mass of air moving bodily for- 
ward, and it impinges on a face or a gas flame with some force. 
It is differentiated from the rest of the atmosphere by reason of 
its peculiar rotational motion, 
The cores of these rings are elastic—they possess rigidity ; 
the circular is their stable form, and if this is altered, they 
oscillate about it. Thus when two vortex rings impinge or even 
approach fairly near one another, they visibly deflect each other, 
aud also cause each other to vibrate. 
The theory of the impact or interference of vortex rings whose 
paths cross, but which do not come very near together has been 
quite recently worked out by Mr. J. J. Thomson. It is quite 
possible to make the rings vibrate without any impact, by ser- 
rating the opening out of which they are knocked. The simplest 
serration of a circle turns it into an ellipse, and here you have 
an elliptic ring oscillating from a tall to a squat ellipse and back 
again. Here is a four-waved opening, and the vibrations are by 
this very well shown. A six-waved opening makes the vibra- 
tions almost too small to be perceived at a distance but still they 
are sometime; distinct. 
The rings vibrate very much like a bell vibrates, perhaps very 
much like an atom vibrates, They have rigidity, although com- 
posed of fluid ; they are composed of fluid in motion. These 
vortices, are imperfect they increase in size, and decrease in 
energy ; in a perfect fluid they would not do this, they would then 
be permnent and indestructible, but then also you would not be 
able to make them. 
Now does not the idea strike you that atoms of matter may be 
vortices like these—vortices in a perfect fluid, vortices in the 
ether. This is Sir William Thomson’s theory of matter. It is 
not yet proved to be true, but is it not highly beautiful? a theory 
abaut which one may almost dare to say that it deserves to be 
true. The atoms of matter according to it are not so much 
foreign particles imbedded in the all-pervading ether as portions 
of it differentiated off from the rest by reason of their vortex 
motion, thus becoming virtually solid particles, yet with no 
transition of substance ; atoms indestructible and not able to be 
manufactured, not mere hard rigid specks, but each composed 
of whirling ether; elastic, capable of definite vibration, of free 
movement, of collision, ‘The crispations or crimpings of these 
rings illustrate the kind of way in which we may suppose an 
atom to vibrate. ‘They appear to have all the properties of 
atoms except one, viz. gravitation; and before the theory can 
be accepted, I think it must account for gravitation, This 
fundamental property of matter cannot be left over to be 
explained by an artificial battery of ultra-mundane corpuscles. 
We cannot go back to mere impact of hard bodies after having 
allowed ourselves a continuous medium, Vortex atoms must be 
shown to gravitate, 
But then remember how small a force gravitation is. Ask any 
educated man whether two pound-masses of lead attract each other, 
and he will reply no. He is wrong, of course, but the force is 
exceedingly small. Yet it is the aggregate attraction of trillions 
upon trillions of atoms ; the s/ighéest effect of each upon the ether 
would be sufficient to account for gravitation ; and no one can 
