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the elements severally, and then in a second part dis- 
cuss the various regions of the earth. 
Undoubtedly as a general introduction to climatic 
studies some such textbooks as those mentioned above 
are an essential on which to build, but there remains 
still an indefinite desire for a new approach; perhaps 
this desire cannot be satisfied in any work which em- 
braces the whole world in its purview and we must be 
content to treat the regions in turn. 
The Demands of Aviation Climatology 
Fifteen or twenty years ago a new demand arose. 
Aviation was spreading. The new machine could be 
persuaded to cover longer and longer distances. Weather 
was all-important, but the machine flew out of the 
weather map—and indeed we were ignorant of how: we 
could use a weather map in the tropics even if we had 
observations with which to make one. The aviator 
clamoured for guidance for his flight and none could 
be given but the data of the climatologist. He was 
shown temperature and rainfall maps and the data 
accumulated in Knox’s Climate of the Continent of Africa 
[20]. The rude aviator said that was not what he wanted. 
He did not greatly care if it were hot or cold. He wanted 
to know about the winds, and even so he was not flying 
on the ground. He was more interested in cloud than 
rain. He did not mind getting wet; what he wanted was 
to see where he was going. The International Commis- 
sion on Air Navigation had indeed, in its wisdom, 
recommended that frequency summaries should be 
made of upper winds, of visibility, and of cloud heights. 
But as yet there were no frequencies for Africa and 
there would not be any for many years. But the rude 
aviator said he was flying to the Cape forthwith and 
he could not fly on Knox. 
Clearly a new type of climatology was needed— 
descriptive rather than statistical—a translation by 
the meteorologist of means and summaries into some- 
thing that the aviator could comprehend. In this, 
synoptic training came to the help of the climatologist. 
He was forced back onethe physical processes underly- 
ing Knox’s data and on their basis described what he 
expected the clouds and the winds would be. In this, 
the idea of air-mass characteristics was ever-present on 
the lines developed by J. Bjerknes and applied to the 
world at large by Bergeron [7], but in those days (the 
twenties) the method had been little applied in detail 
and the tropical air masses were even less comprehended 
than they are today. For the African Continent, with 
which our rude aviator was concerned, much help was 
obtained from the analysis by Brooks and Mirrlees 
[11]. In those days, when the writing of descriptive 
climatology was so little developed, some passages in 
Braak’s ‘Climate of the Netherlands Indies” [9] were an 
inspiration, particularly the one in which he described 
the scene from Mount Pangerango and the changes of 
the clouds in their regular daily variation. This recalled 
the same sequence visible from the Malayan Moun- 
tains; but, and here is the necessary caution, it was 
remembered that the sequence may break and for 
CLIMATOLOGY 
some days give place to another and different order of 
events. Why? The facile answer is ‘a change in air 
mass,” but the physical basis has not yet been explained. 
The Description of Climate by Air Masses 
During the latter part of the second decade of this 
century, air-mass analysis came to the fore under the 
lead of Bergeron [7] and Schinze [26]. The conception 
was that there are definite regions in which the air 
tends to become horizontally homogeneous. These re- 
gions are those where the surface of the earth is uni- 
form, whether land or sea, and where winds are light 
for a sufficiently long time for the properties of the 
atmosphere to reach equilibrium. These regions were 
defined as source regions. As air drifted from a source 
region over some other surface, modification took place 
and the structure and characteristics of the air mass 
changed with time. 
In 1980 Bergeron [7] propounded the use of air masses 
as a method of describing climate that would give a 
picture less static than that given by monthly normals. 
In the same year Linke and Dinies [23] formulated 
a system of designation of air masses for central 
Europe, which Dinies [12] used in 1932 to assess the 
frequency with which Germany lay under the influence 
of different air masses, denominated in eight classes, 
depending on their origin and their track. This paper 
was, it would seem, the first serious attempt to present 
the climate of a region as an entity built up from the 
characteristics of the air masses. Average values were 
obtained for temperature and humidity at the surface 
in each type of air. Frequencies of those air masses, 
given in numerous tables, are summarized in Table I. 
Dinies’ investigation was focussed on Frankfurt am 
Main. The results were of considerable interest, show- 
ing up, as would be expected, the strong contrast 
between air of tropical and polar origins, not only in 
temperature but also in humidity and cloudiness. The 
bitter polar continental air of winter stands out in 
strong contrast to the moist and mild tropical maritime 
air, a contrast stronger indeed than between any of the 
summer air masses. For comparison with Table I it 
may be mentioned that Belasco [6] has given a mean 
winter temperature of —1C for arctic air which had 
arrived at Kew Observatory via Russia and Germany. 
On the other hand he gives the mean value of tempera- 
ture in tropical air in winter as 10C. 
Dinies also surveyed the frequency with which the 
air masses penetrated to the several parts of Germany. 
He showed this by means of maps of the average num- 
ber of days on which the different air masses were over 
various places in Germany. These maps are on an 
annual basis and they show the not unexpected effect 
of penetration of maritime air from the west and south- 
west and the countersurging of continental air from the 
east, as well as the sweep of the polar and polar conti- 
nental air from the northeast. 
The object of Dinies’ treatment was to present cli- 
matology in a much more dynamic picture than had 
been possible in the past when the climatologist dealt 
