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1 877.] Probable Origin and Age of the Sun. 
they get their existence ? It is just as easy to conceive that 
they always existed in motion as to conceive that they always 
existed at rest. In fadf, this is the only way in which energy 
can remain in a body without dissipation into Space. Under 
other forms a certain amount of the energy is constantly being 
transformed into heat which never can be re-transformed 
back again, but is dissipated into Space as radiant heat. But 
a body moving in void stellar space will, unless a collision 
takes place, retain its energy in the form of motion untrans- 
formed for ever. 
It will perhaps be urged as an objection that we have no 
experience of bodies moving in space with velocities ap- 
proaching to anything like 400 or 600 miles per second. A 
little consideration will, however, show that this is an ob- 
jection which can hardly be admitted, as we are not in a 
position to be able to perceive bodies moving with such 
velocities. No body moving at the rate of 400 miles per 
second could remain as a member of our solar system. 
Beyond our system, the only bodies visible to us are the 
nebulae and fixed stars, and they are visible because they are 
luminous. But the fixed stars are beyond doubt suns simi- 
lar to our own ; and if we assume that the energy in the 
form of heat and light possessed by our sun has been derived 
from Motion in Space, we are hardly warranted in denyingthat 
the light and heat possessed by the stars were derived from 
another source. It is true that the motion of the stars in 
relation to one another, or in relation to our system (and 
this is the only motion known to us), is but trifling in com- 
parison to what we even witness in our solar system. But 
this is what we ought, d priori, to expedt ; for if their light 
and heat were derived from Motion in Space, like that of our 
sun, then, like the sun, they must have lost their motion. In 
fadt, they are suns, and visible because they have lost their 
motion . Had not the masses of which these suns were 
composed lost their motion they would have been non- 
luminous, and of course totally invisible to us. In short, 
we only see in stellar space those bodies which, by coming 
into collision, have lost their motion, for it is the lost motion 
which renders them luminous and visible.* 
* When the Foregoing theory of the origin of the sun’s heat was advanced, 
in 1868, I was not aware that a paper on the Physical Constitution of the 
Sun arid Stars ” had been read before the Royal Society by Mr. G. Johnstone 
§toriey, iri which he suggested that the heat possessed by the stars may have 
"been derived from collisions with one another. “ If two stars,” he says, 
should be brought by their proper motion very close, one of three things would 
happen Either they would pass quite clear of one another, in which case 
they would recede to the same immense distance asunder from which they had 
come 5 or they would become so entangled with one another as to emerge 
VOL. VII. (N.S.) £ 
