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~ XXXVIIT. On the new Theory of the System of the Universe. 
By Sir Ricnarp Pues. 
Tue theory which ascribes the subordinate motions on the earth 
to its superior motions as a planet, is opposed by many persons, 
who, assuming that the motions of the planets in a system are 
nevertheless governed by gravitation, ascribe incongruity to a 
new doctrine which excludes that principle from the internal or 
local phenomena of a planet. 
The author of that theory is, however, for good and alae! 
tial reasons, of a totally different opinion. He believes in the 
perfect harmony of nature—in the exact analogy of causes and 
effects—and, wherever he sees motion, he ascribes it to other 
motion ascending i in a series ad infinitum, or to AN UNKNOWN 
causE. He therefore gives no credit whatever to the existence 
of any universal principle of causation, such as that called by 
the name of gravitation, but refers all phenomena to motion, 
primarily and proximately. 
He was not anxious at present to press this extension of his 
theory on the world, because it is less easy to demonstrate that 
distant planets move one another by impulse, than it is to show 
that loose bodies in a ship, or on the earth, are governed in their 
subordinate phenomena by the paramount motions of the ship 
or earth. Every one capable of understanding its terms must 
feel as an axiom, ¢hat the orbicular and rotary motions of the 
earth necessarily give weight to lodies, and laws to their fall, 
because the moving earth and the bodies are in contact, and par- 
taking of those common motions; but certain postulata must 
be granted before it can be proved to beings whose experience 
is confined to the subordinate phenomena of the earth, that dis- 
united planets and masses can operate on each other mecham- 
cally, and communicate motion to one another. 
The postulata required to be admitted are as under :— 
1. That all space is filled with some gaseous medium. 
In the age of Kepler and Newton, the discoveries of Priestley 
had not proved the existence of various gases. An incompressible 
fluid, so light as hydrogen, was not then known to exist.. The 
similar phenomena of the planets ; the combustion of meteors 
at great heights; the transmission of solar and planetary light, 
and the reflection of the solar light after it has been refracted 
through the atmosphere of a comet, prove, however, that some 
rare medium actually fills space; even if its existence were not 
sufficiently proved by the mechanical phenomena of the planets. 
2. The medium of space is acted upon in straight lines by 
moving bodies placed within it. 
It is difficult for men who are accustomed to see the connexion 
of 
