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been computed that if the Andromeda nebula had a density 39,900,000 
that of the sun it would have mass enough to attract the earth as strongly 
as the sun does. It attracts the earth not at all. Nor does it attract any 
other body as far as we know, many of them being much closer to it then we 
we are. 
We do not know the chemical composition of the nebulae, except that it 
see 1s to be different from every thing else in the sky. Not one has ever 
been seen to change its shape, size ot brightness. We have always assumed 
that stars result from the contraction of nebulae and this is based on the idea 
that the nebulae radiate heat. It is not at all certain that these rare gases 
shine because of their heat. A mass of gas of such extreme rarity would have 
a comparatively small amount of heat and it would seem that this ought to 
be radiated into space very rapidly, and could not be miantained without 
rapid contraction. It is quite possible that nebular matter instead of being 
the raw material of stars and planets is matter in some final form after 
having gone through its life history. We have no observational data either 
way and will probably not have any for many centuries to come. There 
does not seem to be any very good reasonifor believing that matter is not 
being created now as much as it ever was nor for thinking that it must always 
endure in some of the forms we now know. 
We think of space as infinite in extent. Whether or not matter, in the 
forms we know, is to be found in all parts of space, we do not know. That 
is to Say we are not yet sure whether the universe is finite or infinite. There 
are some reasons for thinking that the system of the stars is as infinite as 
space itself, but it may also be possible that what we call matter is some mani- 
festation peculiar to this part of space. The mere appearance or disappear- 
ance of matter in space would in itself be no more remarkable than the 
precipitation and evaporation of water would be if we knew nothing of the 
atmosphere, and perhaps not as remarkable as the production of water 
from two invisible and unknown gases would seem to people who know nothing 
of chemistry. 
The most probable source of information it seems to me, will be the 
researches of the physicists and chemists on the real nature of matter. When 
they shall have told us what matter really is, what all of its possible forms 
may be and what all the sources of energy are, then we may be able to state 
with certainty what the life history of a star is, what relation the nebulae 
have to other bodies, and what in reality has been the past history of our 
planet and other planets. 
