e equally distributed over it, it would melt, in the
course of a year, a stratum of ice 46 feet thick, though it covered
the whole globe, and as a consequence the amount of unradiated heat
would render it uninhabitable.

The relative position of the sun affects temperature, rather than its
distance. In winter the earth is three millions of miles nearer the
sun than in summer, but the oblique rays of the former season reach us
in less quantity than the more direct The distribution of land and
water, the nature of the soil, the indentation of bays, the elevation
of land above the sea-level, insularity, etc., all, as we have already
suggested, have a modifying influence on temperature.

The atmosphere possesses also a reflecting and refracting power,
arising from its varying density, and, perhaps, in the latter case,
somewhat from its lenticular outline.

But for this property we should have no twilight. The sun, instead of
sending up his beams while 18 deg. below the visible horizon, would come
upon us out of an intense darkness, pass over our sky a brazen
inglorious orb, and set in an instant amid unwelcome night.

Reflection is the rebound of the rays of light or heat from an
opposing surface at the same angle as that at which they fall upon it.
These are called angles of incidence and reflection, and are equal.

Refraction is the bending of a ray passing obliquely from a rarer into
a denser medium. This may be observed when a rod is placed slantingly
in a vessel of clear water; the part immersed will appear bent or
broken. This is ordinary refraction. Terrestrial refraction is the
same thing, occurring whenever there is a difference of density in the
aerial strata.

The atmosphere absorbs some portion of the light which it receives. It
is not all reflected or refracted or even penetrative.

Objects seen under various degrees of light, either convected or
retarded by different media, appear near or distant, distinct or
confused. Thus, we are often surprised at the apparent nearness and
brightness of an opposite shore or neighboring island, in some
conditions of the air, while at other times they seem distant and lie
in shadowy obscurity.

The looming up of a vessel on the water is another common instance of
the principle of refraction.

It has been noticed by almost every one, that, during the warm and
moist nights of summer, the moon, as she rises above the horizon,
appears much larger than when at the zenit