pparently hopeless desert, even without the intervention of
war and pestilence, if man allows the climate to master him. In many
cases the reports of increasing dryness really concern only the decrease
in the water supply from rivers and springs, and it is well known that a
change in the cultivation of the soil, or in the extent of the forests,
may bring about marked changes in the flow of springs and rivers without
any essential change in the actual amount of rainfall.

Lastly, a region whose normal rainfall is at best barely sufficient for
man's needs may be abandoned by its inhabitants during a few years of
deficient precipitation, and not again occupied even when, a few years
later, normal or excessive rainfall occurs.

_Periodic Oscillations of Climate: Sun-spot Period._--The discovery of a
distinct eleven-year periodicity in the magnetic phenomena of the earth
naturally led to investigations of similar periods in meteorology. The
literature on this subject has assumed large proportions. The results,
however, have not been satisfactory. The problem is difficult and
obscure. Fluctuations in temperature and rainfall, occurring in an
eleven-year period, have been made out for certain stations but the
variations are slight, and it is not yet clear that they are
sufficiently marked, uniform and persistent over large areas to make
practical application of the periodicity in forecasting possible. In
some cases the relation to sun-spot periodicity is open to debate; in
others, the results are contradictory.

W. P. Koppen has brought forward evidence of a sun-spot period in the
mean annual temperature, especially in the tropics, the maximum
temperatures coming in the years of sun-spot minima. The whole amplitude
of the variation in the mean annual temperatures, from sun-spot minimum
to sun-spot maximum, is, however, only 1.3 deg. in the tropics and a
little less than 1 deg. in the extra-tropics. More recently Nordmann
(for the years 1870-1900) has continued Koppen's investigation.

In 1872 C. Meldrum, then Director of the Meteorological Observatory at
Mauritius, first called attention to a sun-spot periodicity in rainfall
and in the frequency of tropical cyclones in the South Indian Ocean. The
latter are most numerous in years of sun-spot maxima, and decrease in
frequency with the approach of sun-spot minima. Poey found later a
similar relation in the case of the West Indian hurricanes. Meldrum's
conclusions regarding ra