by its reflected rays; 3. by contact with the heated surface.
A forest receiving the sun's rays, a part of them enters the intervals
between the trees, and their reflection upwards is intercepted by the
leaves and boughs. The rest fall on the trees, the leaves of which being
generally inclined towards the horizon, reflect the rays downwards. The
atmosphere here, then, receives little or no heat by reflection. Again,
these leaves having a power of keeping themselves cool by their own
transpiration, they impart no heat to the air by contact. Reflection
and contact, then, two of the three modes before-mentioned, of
communicating heat, are wanting here; and, of course, the air over
a country covered by forest must be colder than that over cultivated
grounds.
The sea being pellucid, the sun's rays penetrate it to a considerable
depth. Being also fluid, and in perpetual agitation, its parts are
constantly mixed together; so that instead of its heat being all
accumulated in its surface, as in the case of a solid, opaque body,
it is diffused through its whole mass. Its surface, therefore, is
comparatively cool, for these reasons; to which may be added that of
evaporation.
Pages:
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132