a . NATURE 
[SEPTEMBER II, I913 
14th, or can make the sun South sometimes at eleven 
o’clock sometimes at twelve.* 
But the changes of dimension and mass due to 
velocity are not conventions but realities; so I urge, 
on the basis of the electrical theory of matter. The 
Fitzgerald-Lorentz hypothesis I have an affection for. 
I was present at its birth. Indeed, I assisted at its 
birth; for it was in my study at 21 Waverley Road, 
Liverpool, with Fitzgerald in an armchair, and while 
I was enlarging on the difficulty of reconciling the 
then new Michelson experiment with the theory of 
astronomical aberration and with other known facts, 
that he made his brilliant surmise :—‘‘ Perhaps the 
stone slab was affected by the motion.’’ I rejoined 
that it was a 45° shear that was needed. To which 
he replied, ‘‘ Well, that’s all right—a simple distor- 
tion.” And very soon he said, ‘‘And I believe it 
oceurs, and that the Michelson experiment demon- 
strates it.’’ A shortening long-ways, or a lengthen- 
ing cross-ways would do what was wanted. 
And is such a hypothesis gratuitous? Not at all: 
in the light of the electrical theory of matter such an 
effect ought to occur. The amount required by the 
experiment, and given by the theory, is equivalent to 
a shrinkage of the earth’s diameter by rather less 
than three inches, in the line of its orbital motion 
through the zther of space. An oblate spheroid with 
the proper eccentricity has all the simple geometrical 
properties of a stationary sphere; the eccentricity de- 
pends in a definite way on speed, and becomes con- 
siderable as the velocity of light is approached. 
All this Profs. Lorentz and Larmor very soon after, 
and quite independently, perceived; though this is 
only one of the minor achievements in the electrical 
theory of matter which we owe to our distinguished 
visitor Prof. H. A. Lorentz. 
The key of the position, to my mind, is the nature 
of cohesion. I regard cohesion as residual chemical 
affinity, a balance of electrical attraction over repul- 
sion between groups of alternately charged molecules. 
Lateral electrical attraction is diminished by motion; 
so is lateral electric repulsion. In cohesion both are 
active, and they nearly balance. At anything but 
molecular distance they quite balance, but at molecular 
distance attraction predominates. It is the diminu- 
tion of the predominant partner that will be felt. 
Hence while longitudinal cohesion, or cohesion in the 
direction of motion, remains unchanged, lateral 
cohesion is less; so there will be distortion, and a 
unit cube x, y, 2 moving along x with velocity u 
becomes a parallelopiped with sides 1/k?, k, k; where 
1/k®=1—u?/v?.® 
The electrical theory of matter is a positive achieve- 
ment, and has positive results. By its aid we make 
experiments which throw light upon the relation 
between matter and the zther of space. The prin- 
ciple of relativity, which seeks to replace it, is a 
principle of negation, a negative proposition, a state- 
ment that observation of certain facts can never be 
made, a denial of any relation between matter and 
zether, a virtual denial that the zther exists. Whereas 
if we admit the real changes that go on by reason 
of rapid motion, a whole field is open for discovery ; 
it is even possible to investigate the changes in shape 
of an electron—appallingly minute though it is—as it 
approaches the speed of light; and properties belong- 
5 In the historical case of governmental interference with the calendar, no 
wonder the populace rebelled. Surely someone might have explained to the 
authorities that dropping leap year for the greater part of a century would 
do all that was wanted, and that the borrible inconvenience of upsetting all 
engagements and shortening a single year by eleven days could he avoided, 
6 Different modes of estimating the change give slightly different results ; 
some involve a compression as well as a distortion—in fact the strain asso- 
ciated with the name of Thomas Young ; the details are rather complicated 
and this is not the place to discuss them pure shear, of magnitude 
specified in the text, is simplest, it is in accord with all the experimental 
facts—including some careful measurements by Bucherer—and I rather 
expect it to survive. | 
NO. 2289, VOL. 92] 
ing to the zther of space, evasive though it be, can- 
not lag far behind. 
Speaking as a physicist, I must claim the zther as 
peculiarly our own domain. The study of molecules 
we share with the chemist, and matter in its various 
forms is investigated by all men of science, but a 
study of the zther of space belongs to physics only. 
I am not alone in feeling the fascination of this por- 
tentous entity. Its curiously elusive and intangible 
character, combined with its universal and unifying 
permeance, its apparently infinite extent, its definite 
and perfect properties, make the zther the most 
interesting, as it is by far the largest and most funda- 
mental, ingredient in the material cosmos. 
As Sir J. J. Thomson said at Winnipeg— 
“The zether is not a fantastic creation of the specu- 
lative philosopher; it is as essential to us as the air 
we breathe. . . . The study of this all-pervading sub- 
stance is perhaps the most fascinating and important 
duty of the physicist.” 
Matter it is not, but material it is; it belongs to 
the material universe, and is to be investigated by 
ordinary methods, But to say this is by no means 
to deny that it may have mental and spiritual func- 
. tions to subserve in some other order of existence, as 
. matter has in this. 
The zther of space is at least the great engine of 
continuity. It may be much more, for without it 
there could hardly be a material universe at all. 
Certainly, however, it is essential to continuity; it is 
the one all-permeating substance that binds the whole 
of the particles of matter together. It is the uniting 
and binding medium without which, if matter could 
exist at all, it could exist only as chaotic and isolated 
fragments: and it is the universal medium of com- 
munication between worlds and particles. And yet it 
is possible for people to deny its existence, because it 
is unrelated to any of our senses, except sight—and 
to that only in an indirect and not easily recognised 
fashion. 
To illustrate the thorough way in which we may be 
unable to detect what is around us unless it has some 
link or bond which enables it to make appeal, let me 
make another quotation from Sir J. J. Thomson’s 
address at Winnipeg in 1909. He is leading up to 
the fact that even single atoms, provided they are 
fully electrified with the proper atomic charge, can be 
detected by certain delicate instruments—their field of 
force bringing them within our ken—whereas a whole _ 
crowd of unelectrified ones would escape observation. - 
“The smallest quantity of unelectrified matter ever 
detected is probably that of neon, one of the inert 
gases of the atmosphere. Prof. Strutt has shown that 
the amount of neon in 1/20 of a cubic centimetre of 
the air at ordinary pressures can be detected by the 
spectroscope; Sir William Ramsay estimates that the 
neon in the air only amounts to one part of neon in 
100,000 parts of air, so that the neon in 1/20 of a 
cubic centimetre of air would only occupy at atmo- 
spheric pressure a volume of half a millionth of a 
cubic centimetre. When stated in this form the quan- 
tity seems exceedingly small, but in this small volume 
there are about ten million million molecules. Now 
the population of the earth is estimated at about 
fifteen hundred millions, so that the smallest number 
of molecules of neon we can identify is about 7000 
times the population of the earth. In other words, 
if we had no better test for the existence of a man 
than we have for that of an unelectrified molecule we. 
should come to the conclusion that the earth is un- 
inhabited.” 
The parable is a striking one, for on these lines it 
might legitimately be contended that we have no 
right to say positively that even space is uninhabited. 
All we can safely say is that we have no means of 
