of
transferable inventions. Little has been done in a systematic way on
this topic, but the rapidity with which a really important change in
equipment and organization passes from camp to camp, and revolutionizes
not only armies but states, when it is a question of survival or defeat,
has its illustration in many phases of warfare, and ranks among the
great levellers of national or regional pride.

The recorded movements of peoples in historic times, and the previous
movements inferred from language, and other symptoms, indicate a
long-established distribution of what might be described in
meteorological phrase as _man-pressure_; certain regions being
characterized either always or repeatedly by high man-pressure, and an
outward flow of men into the cyclonic areas or vortexes of low
man-pressure in the human covering (or biosphere) of the planet. Typical
high-pressure regions are the Arabian peninsula with its repeated crises
of Semitic eruption, and the great Eurasian grasslands. Typical regions
of low man-pressure, and repeated irruption, are the South European
peninsulas. Occasionally a region plays both parts, alternately
accepting inhabitants, and unloading them on to other lands; examples
are the Hungarian plain, Scandinavia, and Britain. Others again can
hardly be said to have a population of their own at all, but are simple
avenues of transmission, like Western Switzerland and the Hellespont
Region. I am speaking now, of course, about ancient times. The causes of
these recurrent movements are not clearly made out; but the movements
themselves, and the fact that they are of regional recurrence, are
matters of history.

Conspicuous among such movements are the westward drift from Asia into
peninsular Europe, in its three parallel columns, through tundra,
forest, and steppe; and the southward drifts, subsidiary to this, from
East Central Europe into the Balkan lands and round the head of the
Adriatic. The course of these drifts is laid out in detail, as we have
seen, by the physique of the regions; and therewith is determined the
kind of life which each set of folk must be living if it is to survive
the journey.

And here we come at once upon a new factor making strongly for a more
general uniformity of culture within peninsular Europe than its physical
character would at all prepare us to expect. For although individual men
often respond very rapidly to fresh surroundings, and can change their
mode of life al