scheme of the sub-climates for the lowlands, with their names. Four climates which do not occur at sealevel are here lacking (C7, E3, E4, F).

The verti

FIG. 14. VERTICAL DISTRIBUTION OF CLIMATES

cal distribution of these climates, much simplified, is shown in Fig 14. The descent of the climatic strata from equator to higher latitudes is shown on the right for the continental, and on the left for the marine type, as far as about latitude 57°. Climates C1 to C4, and D1 and D2, have large temperature ranges, and are therefore lacking at the equator and on the ocean; while C5 to C7, and D3, have small ranges, and are not found on the continents in higher latitudes. The general control of pressure, winds, and ocean currents over the climatic types is shown in the two following ideal diagrams, in which the two vertical lines indicate the west and east coasts of the ideal continent, and the area included reaches to the middle of the ad

expression which combines the effect of rainfall and evaporating power. r=rain probability of rainiest month.

1 C7, High savanna climate; E3, Yak, or Pamir climate; E4, Chamois or high alpine climate; F, perpetual frost, without life.

jacent ideal oceans. The line 0°-0° is the equator (Figs. 15 and 16). The short arrows give the wind direction 500-1000 metres above the surface; calms are represented by the sign o; the long broken arrows

FIG. 15. PRESSURE AND WINDS IN JANUARY

indicate the prevailing surface ocean currents. At a a there is a rise of cold water from beneath the surface of the ocean. The curving lines are sea-level isobars; the lower pressures are shaded. The letters and

boundaries, drawn in short, slanting lines in Fig. 16 indicate the climatic districts of Fig. 11. Fig. 15 is similar to Fig. 16, as far as these climatic districts are

concerned.

Therefore the letters and boundaries

are omitted. Fig. 17 shows the geographical distribution of the climatic types and sub-types.

Ravenstein's Hygrothermal Types. Recognising

the importance of relative humidity as a climatic factor in its influence upon life, upon agriculture and upon industry, and basing his grouping of climates upon certain relations between temperature and relative humidity, Ravenstein proposes a subdivision of the earth's surface into sixteen hygrothermal climatic types. The general characteristics and examples of these types are as follows:

1. Hot (73° and over) and very damp (humidity 81% or more): Batavia, Cameroons, Mombasa.

2. Hot and moderately damp (66-80%): Havana, Calcutta.

3. Hot and dry (51-65%): Bagdad, Lahore, Khartum.

4. Hot and very dry (50% or less): Disa, Wadi Halfa, Kuka.

5. Warm (58° to 72°) and very damp: Walfish Bay, Arica.

6. Warm and moderately damp: Lisbon, Rome, Damascus, Tokio, New Orleans.

7. Warm and dry: Cairo, Algiers, Kimberley. 8. Warm and very dry: Mexico, Teheran.

9. Cool (33° to 57°) and very damp: Greenwich, Cochabamba.

10. Cool and moderately damp: Vienna, Melbourne, Toronto, Chicago.

11. Cool and dry: Tashkent, Simla, Cheyenne. 12. Cool and very dry: Yarkand, Denver.

13. Cold (32° or less) and very damp: Ben Nevis, Sagastyr, Godthaab.