iction against the air they are raised to incandescence and caused
to emit light and heat. At certain seasons of the year they shower
down upon us in great numbers. In Boston 240,000 of them were
observed in nine hours. There is no reason to suppose that the
planetary system is limited to 'vast masses of enormous weight;' there
is, on the contrary, reason to believe that space is stocked with
smaller masses, which obey the same laws as the larger ones. That
lenticular envelope which surrounds the sun, and which is known to
astronomers as the Zodiacal light, is probably a crowd of meteors; and
moving as they do in a resisting medium, they must continually
approach the sun. Falling into it, they would produce enormous heat,
and this would constitute a source from which the annual loss of heat
might be made good. The sun, according to this hypothesis, would
continually grow larger; but how much larger? Were our moon to fall
into the sun, it would develope an amount of heat sufficient to cover
one or two years' loss; and were our earth to fall into the sun a
century's loss would be made good. Still, our moon and our earth, if
distributed over the surface of the sun, would utterly vanish from
perception. Indeed, the quantity of matter competent to produce the
required effect would, during the range of history, cause no
appreciable augmentation in the sun's magnitude. The augmentation of
the sun's attractive force would be more sensible. However this
hypothesis may fare as a representant of what is going on in nature,
it certainly shows how a sun _might_ be formed and maintained on known
thermo-dynamic principles.

Our earth moves in its orbit with a velocity of 68,040 miles an hour.
Were this motion stopped, an amount of heat would be developed
sufficient to raise the temperature of a globe of lead of the same
size as the earth 384,000 degrees of the centigrade thermometer. It
has been prophesied that 'the elements shall melt with fervent heat.'
The earth's own motion embraces the conditions of fulfilment; stop
that motion, and the greater part, if not the whole, of our planet
would be reduced to vapour. If the earth fell into the sun, the
amount of heat developed by the shock would be equal to that developed
by the combustion of a mass of solid coal 6435 times the earth in
size.

There is one other consideration connected with the permanence of our
present terrestrial conditions, which is well worthy of our a