26 PRESIDENTS ADDRESS. 
rejoined that it was a 45° shear that was needed. To which he replied, 
‘ Well, that’s all right,—a simple distortion.’ And very soon he said, 
‘And I believe it occurs, and that the Michelson experiment demon- 
strates it.’ A shortening long-ways or a lengthening cross-ways ~ 
would do what was wanted. (See Nature for June 16, 1892, p. 165.) 
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 ether of 
space. An oblate spheroid with the proper excentricity has all the 
simple geometrical properties of a stationary sphere; the excentricity 
depends in a definite way on speed, and becomes considerable as the 
velocity of light is approached. 
All this Professors Lorentz and Larmor very soon after, and quite 
independently, perceived ; though this is only one of the minor achieve- 
ments in the electrical theory of matter which we owe to our dis- 
tinguished visitor, Professor 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 repulsion between groups of alternately charged mole- 
cules. 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 diminution 
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 Z moving along x with velocity u becomes a parallelopiped with 
sides 1/k?, k, k; where 1/k*=1—u?/v?.5 
The Bisstscal theory of matter is a positive achievement, and has 
positive results. By its aid we make experiments which throw light 
upon the relation between matter and the Ether of Space. The 
Principle of Relativity, which seeks to replace it, is a principle of 
negation, a negative proposition, a statement that observation of 
certain facts can never be made, a denial of any relation between 
matter and ether, a virtual denial that the ether exists. Whereas if 
we admit the real changes that go on by reason of rapid motion, a 
5 Different modes of estimating the change give slightly different results; 
some involve a compression as well as a distortion—in fact the strain associated 
with the name of Thomas Young; the details are rather complicated and this is 
not the place to discuss them. A pure distortion, as specified in the text, is 
simplest; it appears to be in accord with all the experimental facts—including 
some careful measurements by Bucherer,—and I rather expect it to survive. 
