PRESIDENTS ADDRESS. 25 
Visibility depends on radiation, on differential radiation. | We must 
have differences to appeal to our senses; they are not constructed for 
uniformity. _ 
It is the extreme omnipresence and uniformity and universal agency 
of the ether of space that makes it so difficult to observe. To observe 
anything you must have differences. If all actions at a distance are 
conducted at the same rate through the ether, the travel of none of 
them can be observed. Find something not conveyed by the ether 
and there is a chance. But then every physical action is trans- 
mitted by the ether, and in every case by means of its transverse or 
radiation-like activity. 
Except perhaps Gravitation. That may give us a clue some day, 
but at present we have not been able to detect its speed of transmission 
at all. No plan has been devised for measuring it. Nothing short 
of the creation or destruction of matter seems likely to serve: creation 
or destruction of the gravitational unit, whether it be an atom or an 
electron or whatever it is. Most likely the unit of weight is an electron, 
just as the unit of mass is. 
The so-called non-Newtonian Mechanics, with mass and shape 
a function of velocity, is an immediate consequence of the electrical 
theory of matter. The dependence of inertia and shape on speed is 
a genuine discovery and, I believe, a physical fact. The Frinciple 
of Relativity would reduce it to a conventional fiction. It would 
seek to replace this real change in matter by imaginary changes in 
time. But surely we must admit that Space and Time are essentially 
unchangeable: they are not at the disposal even of mathematicians; 
though it is true that Pope Gregory, or a Daylight-saving Bill, can 
play with our units, can turn the 3rd of October in any one year 
into the 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 recon- 
ciling the then new Michelson experiment with the theory of astrono- 
mical aberration and with other known facts, that he made his brilliant 
surmise :—‘ Perhaps the stone slab was affected by the motion.’ I 
* 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 horrible inconvenience of upsetting all engage- 
ments and shortening a single year by eleven days could be avoided. 
