----+
|Altitude of sun | O | 5 | 10 | 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 |
| |deg.|deg.|deg.|deg.|deg.|deg.|deg.|deg.|deg.|deg.|deg.|
| | | | | | | | | | | | |
|Relative lengths | | | | | | | | | | | |
| of path through | | | | | | | | | | | |
| the atmosphere |44.7|10.8|5.7 |2.92|2.00|1.56|1.31|1.15|1.06|1.02|1.00|
| | | | | | | | | | | | |
|Intensity of | | | | | | | | | | | |
| radiation on a | | | | | | | | | | | |
| surface normal | | | | | | | | | | | |
| to the rays | 0.0|0.15|0.31|0.51|0.62|0.68|0.72|0.75|0.76|0.77|0.78|
| | | | | | | | | | | | |
|Intensity of | | | | | | | | | | | |
| radiation on | | | | | | | | | | | |
| a horizontal | | | | | | | | | | | |
| surface | 0.0|0.01|0.05|0.17|0.31|0.44|0.55|0.65|0.72|0.76|0.78|
+------------------+----+----+----+----+----+----+----+----+----+----+----+

_Physical Climate._--The distribution of insolation explains many of the
large facts of temperature distribution, for example, the decrease of
temperature from equator to poles; the double maximum of temperature on
and near the equator; the increasing seasonal contrasts with increasing
latitude, &c. But the regular distribution of solar climate between
equator and poles which would exist on a homogeneous earth, whereby
similar conditions prevail along each latitude circle, is very much
modified by the unequal distribution of land and water; by differences
of altitude; by air and ocean currents, by varying conditions of
cloudiness, and so on. Hence the climates met with along the same
latitude circle are no longer alike. Solar climate is greatly modified
by atmospheric conditions and by the surface features of the earth. The
uniform arrangement of solar climatic belts, arranged latitudinally, is
interfered with, and what is known as _physical climate_ results.
According to the dominant control we have solar, continental and marine,
and mountain climates. In the first-named, latitude is the essential; in
the second a