ible vapor. This is especially true on a warm day; the same process
takes place in the air that is going on at the level of a body of water
or at the surface of moist earth.

As before stated, condensation always takes place when a body of
moisture-laden air comes in contact with cold. When the steam escapes
from a boiler, even on the hottest day, it is hotter than the
surrounding air; the first effect is condensation, and then evaporation
takes place the same as it would at the surface of the earth when the
condensed particles of moisture are separated into the invisible atoms
that accompany evaporation.

In settled, dry weather as the sun approaches the zenith, the earth
becomes intensely heated, and there is an ascending column of air partly
laden with moisture; but not to the same extent as earlier in the
season. Condensation takes place and clouds are formed, but as there is
not sufficient moisture to carry them to the point of a further
condensation,--which would result in precipitation,--as the sun lowers
in the west and the heated air becomes more evenly distributed this
condensed vapor is reabsorbed into the air as invisible moisture by a
process allied to that of evaporation. This condition of things would
extend to a much longer period than it does in our latitude if it were
not for the gradual changing of the seasons, which finally destroys the
balance in the dynamics of cloud-land and allows the cold--that has been
held back for the time--in the great northern zone to get the upper
hand. Then we have what is termed in common parlance a change in the
weather, or, more properly in this case, a change in the season.

We have already spoken of the cloud called cumulus (which means heap)
and of its performance during the dry season of summer. There is another
form of cloud that is seen at this season of the year called cirrus (a
curl). It takes the form of a curl at its ends. This cloud usually has a
threaded shape and sometimes takes the form of a feather, and frequently
forms are seen that remind you of frost pictures on a window pane. These
clouds float very high in the atmosphere, away above the tops of the
highest mountains, from six to eight miles above the level of the sea.
They are formed only at a season of the year when the atmospheric
conditions are most uniform. At certain times of the day and night the
moisture will rise to this height before it condenses and when it does
condense it immediately f