Nearly all the heat of the sun passes through glass without hinderance;
but take heat from white-hot platinum and only seventy-six per cent.
of it goes through glass, twenty-four per cent. being so constituted
that it cannot pass with facility. Of heat from copper at 752°
only six per cent. can go through glass, the other ninety-four per
cent. being absorbed by it.

The heat of the sun beam goes through glass without [Page 34] any
hinderance whatever. It streams into the room as freely as if there
were no glass there. But what if the furnace or stove heat went
through glass with equal facility? We might as well try to heat our
rooms with the window-panes all out, and the blast of winter
sweeping through them.

The heat of the sun, by its intense vibrations, comes to the earth
dowered with a power which pierces the miles of our atmosphere,
but if our air were as pervious to the heat of the earth, this
heat would flyaway every night, and our temperature would go down
to 200° below zero. This heat comes with the light, and then,
dissociated from it, the number of its vibrations lessened, it is
robbed of its power to get away, and remains to work its beneficent
ends for our good.

Worlds that are so distant as to receive only 1/1000 of the heat
we enjoy, may have atmospheres that retain it all. Indeed it is
probable that Mars, that receives but one-quarter as much heat
as the earth, has a temperature as high as ours. The poet drew on
his imagination when he wrote: