richness or barrenness of a country, but also its very shape; the
rate at which the hills are destroyed and washed into the lowland;
the rate at which the seaboard is being removed by the action of
waves--all these are branches of study which is becoming more and
more important.

And even in the study of animals and their effects on the
vegetation, questions of really deep interest will arise. You will
find that certain plants and trees cannot thrive in a district,
while others can, because the former are browsed down by cattle, or
their seeds eaten by birds, and the latter are not; that certain
seeds are carried in the coats of animals, or wafted abroad by
winds--others are not; certain trees destroyed wholesale by insects,
while others are not; that in a hundred ways the animal and
vegetable life of a district act and react upon each other, and that
the climate, the average temperature, the maximum and minimum
temperatures, the rainfall, act on them, and in the case of the
vegetation, are reacted on again by them. The diminution of
rainfall by the destruction of forests, its increase by replanting
them, and the effect of both on the healthiness or unhealthiness of
a place--as in the case of the Mauritius, where a once healthy
island has become pestilential, seemingly from the clearing away of
the vegetation on the banks of streams--all this, though to study it
deeply requires a fair knowledge of meteorology, and even of a
science or two more, is surely well worth the attention of any
educated man who is put in charge of the health and lives of human
beings.

You will surely agree with me that the habit of mind required for
such a study as this, is the very same as is required for successful