nd minima, and a
marine climate, therefore, has a cool spring and a warm autumn, the
seasonal changes being but slight. Characteristic, also, of marine
climates is a prevailingly higher relative humidity, a larger amount of
cloudiness, and a heavier rainfall than is found over continental
interiors. All of these features have their explanation in the abundant
evaporation from the ocean surfaces. In the middle latitudes the oceans
have distinctly rainy winters, while over the continental interiors the
colder months have a minimum of precipitation. Ocean air is cleaner and
purer than land air, and is generally in more active motion.

_Continental Climate._--Continental climate is severe. The annual
temperature ranges increase, as a whole, with increasing distance from
the oceans. The coldest and warmest months are usually January and July,
the times of maximum and minimum temperatures being less retarded than
in the case of marine climates. The greater seasonal contrasts in
temperature over the continents than over the oceans are furthered by
the less cloudiness over the former. Diurnal and annual changes of
nearly all the elements of climate are greater over continents than over
oceans; and this holds true of irregular as well as of regular
variations. Fig. 3 illustrates the annual march of temperature in marine
and continental climates. Bagdad, in Asia Minor (Bd.), and Funchal on
the island of Madeira (M.) are representative continental and marine
stations for a low latitude. Nerchinsk in eastern Siberia (N.) and
Valentia in south-western Ireland (V.) are good examples of continental
and marine climates of higher latitudes in the northern hemisphere. The
data for these and the following curves were taken from Hann's _Lehrbuch
der Meteorologie_ (1901).

Owing to the distance from the chief source of supply of water
vapour--the oceans--the air over the larger land areas is naturally
drier and dustier than that over the oceans. Yet even in the arid
continental interiors in summer the absolute vapour content is
surprisingly large, and in the hottest months the percentages of
relative humidity may reach 20% or 30%. At the low temperatures which
prevail in the winter of the higher latitudes the absolute humidity is
very low, but, owing to the cold, the air is often damp. Cloudiness, as
a rule, decreases inland, and with this lower relative humidity, more
abundant sunshine and higher temperature, the evaporating power of a
c