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A RETROSPECT OF WIRELESS COMMUNICATION. 555 
theory agreed to a sufficient approximation, and the theory is then said to be complete. 
Iam only taking this as a typical instance of the way in which mathematics is applied 
to physics, to secure in this instance a trivial result. Of course, a mathematician 
might have taken the whole into account at first, and then the theory would have 
been complete from the beginning, and there would have been nothing to correct 
afterwards. 
That was the kind of way in which Newton proceeded. When he gave his theory 
of astronomy based upon gravitation he at first took the heavenly bodies first as 
particles, then as spheres, and thus arrived at a first approximation to the theory 
of their motions. But he knew that the earth itself could not be a sphere, because 
it was spinning on its axis; it must be an oblate spheroid. That had never been 
observed, but Newton predicted that it was so, and proceeded to trace the remote 
consequences of the shape of the earth. He found that it accounted for the precession 
of the Equinoxes, which had been known as an empirical fact to the Ancients. 
Copernicus had said that precession must represent a conical motion of the earth’s 
axis; but no one knew any cause for such a conical motion. Newton with his extra- 
ordinary genius perceived that a conical motion, very slow, and taking thousands of 
years for its revolution, would be the exact result following from the pull of gravitation 
on an oblate spheroid. A spheroid would not act as if all its mass were concentrated 
at its centre ; it would be more complicated than that. He was not deterred by the 
complications, but worked them out and completed his theory. 
Another thing that had been ignored in the first view of astronomy was the size 
and plasticity of the bodies; they were treated as particles or rigid bodies, and this 
gave the first approximation. But, obviously, the earth is not a particle but a body of 
considerable size, so that some parts of it are appreciably nearer the sun or the moon 
than are the parts at the Antipodes. Newton took the size into account, and thus 
was able to show that anything yielding or mobile on the surface of the earth, like 
the ocean, would have a motion distinct from the rest of the earth to a slight extent, 
and would go through an oscillation periodically. This oscillation of the water on 
the earth he perceived would account for a phenomenon that had been known from 
antiquity, but had never been explained, namely, the Tides. He completed his theory 
by working out the tides in all their main detail, leaving it to others to show how great 
an effect tidal phenomena had had on the evolution of the universe. 
This has been recently extended and applied by Sir James Jeans to the production 
of a solar system. He has shown mathematically that if a visiting sun entered our 
neighbourhood, coming within a reasonable distance of our sun, it would excite tides 
upon the sun, which might increase to such an extent as to throw out an explosion or 
protuberance. The history of this he followed up, and showed that it would presently 
aggregate into round bodies revolving round the earth, the bigger ones in the middle 
of the protuberance, the smaller ones at either end, and thus provide the sun with 
a system of planets, on one of which we happen to live. Well, that is a further develop- 
ment of tidal theory, taking into account all the possibilities, or at any rate such of 
them as a genius is able to consider relative, and giving an idea which at present seems 
likely to hold against adverse criticism about the origin or creation of the earth and 
_ other planets. This again is a digression, and I do not see how the theory is to be 
verified by experiment. All this development could not be done by one man; the 
genius who made it possible is Isaac Newton. The further developments of his theory 
were left to posterity. 
So it was also with Clerk Maxwell. He wrote down some equations which expressed 
what Faraday had long brooded over as the electric field, regarding it as distinct 
from matter and existing in the ether of space around the charged body. He also 
wrote down another set of equations expressing the magnetic field surrounding a 
current. And then he began to combine these, so as to see what an electromagnetic 
field would be like, that is to say, a field which combined an electric displacement with 
a magnetic whirl. Do not suppose that this was an easy thing to do, but Maxwell 
did it, and found (possibly to his surprise, possibly to a satisfaction of his instinct in 
that direction), that the equation he now got, a differential equation of the second 
order, was one that was familiar to him and to other mathematicians, namely, the 
equation to a wave ; that is, a disturbance periodic in space and time, which advanced 
through space at a certain rate. This rate was expressed by an electric and a magnetic 
constant of the ether, which were immeasurable ; no one knows to this day how to 
measure them. But the rate of propagation of the electromagnetic wave did not 
