242 
WAT ORE 
[JANUARY IO, 190, 
hemispheres unite, and 
there is no longer a division at the equator. This is 
the great summer monsoon of southern Asia, which 
in the whole world has nothing to compare with it. 
In this, as in succeeding pressure charts, it is seen 
that in many places the winds recorded are in opposi- 
tion to the distribution of pressure (local disturb- 
ances?). In the January chart we miss the north- 
west monsoon over the Malay Archipelago (it is found 
North Australia), although at Batavia, for ex- 
ample, west, north-west, and north winds prevail in 
January with a frequency of more than 80 per cent., 
and similarly also prevail in strength. 
Plates xi.-xxiii. exhibit the distribution of mean 
pressure and the winds for each month and the year 
at 8 a.m., the hour of observation for the telegrams 
for the Daily Weather Report. Besides these there 
are two smaller charts showing the pressure and 
wind at 10 a.m. and also at 4 p.m., that is, at the 
hours of the daily extremes. In the quiet, cool- 
weather season the winds experienced undergo 
changes of direction in accordance with the distribu- 
tion of pressure. In the Ganges valley, in May, at 
4 p-m., they appear to blow against the gradient, 
that is,.from the lower to the higher pressure, the 
problem of the mnor’-westers, which had already 
occupied the attention of Blanford. 
Plates xxiv.-xxxvi. show the mean pressure and 
the winds for the day, the smaller charts the actual 
diurnal range of pressure, and the range reduced to 
sea-level, monthly and annual. From January to 
May, in southern India, the daily range of pressure 
is as much as o-r5 inch to 0.17 inch; during and 
after the rainy season it diminishes to 0.13 inch or 
0-12 inch. These great daily amplitudes justify the 
representation of the mean daily distribution of pres- 
sure. In Plates xi.-xxxvi. the monthly and annual 
isobars are drawn at intervals of 0.05 inch, an interval 
which would be ample for Europe, but for a tropical 
region it appears to be too large. The pressure 
gradient which sets the great south-west monsoon in 
motion does not amount to so much as 0.02 inch per 
degree. We see, therefore, upon some charts— 
February, March, October, and November—only two 
to four isobars over the whole of the extensive region, 
and sometimes it is not very clear as to the local 
decrease of pressure, especially over the Bay towards 
the east. This could have been easily remedied by 
specially noting the mean pressure at the Nicobars, 
Andamans, and on the coast of Burma. 
As to the origin of the most interesting pheno- 
menon in the meteorology of India—the bursting of 
the monsoon—the charts which lie before us cannot 
afford sufficient explanation, for the origin lies outside 
the limits of the charts, far southward in the Indian 
Ocean, not over the Indian land region, as Sir John 
Eliot pointed out (Quarterly Journal of the Royal 
Meteorological Society, January, 1896). The gradual 
advance of the southern and western sea breezes in 
the mighty south-west monsoon we see in the charts 
for February and March to June. The south-west 
monsoon reaches Ceylon about the middle of May, 
NO. 1941, VOL. 75] 
the southern and northern 
over 
and arrives at Bombay about the middle of June. So 
gradual does the advance seem from April to May 
and from May to June that it is scarcely noticeable 
in the charts; but we do, however, find an indication. 
On the May and June charts we see a higher pressure 
advancing south and south-west, while in 
northern India pressure is decreasing. A pressure 
wave spreads over India from May to June. This is 
clearly shown in the following pressure changes from 
month to month :— 
from 
Changes from 
Apa Mey May-June June-July 
oth n. 
Zanzibar 6128S. .. +0°066... +0°069 ... +0°0I19 
Colombo ... 654.N.... —o'014. +0°009... +0'016 
Trivandrum 8 30 N. ... —0°007 ... +0°003 ... +0'009 
Mooltan 30 12 N. ... ~O°840)... —Ot147) 28 OOO 
Dera Ismail Khan 32 ON. ... —O°145... -O' 161 ... —O'013 
From May to June southern facia is flooded with 
masses of air from the ocean by the south-west mon- 
soon, while over north-west India pressure continues 
to give way. 
Plates xxxvii.-xlix. contain the monthly and anuual 
mean temperatures over India, the isotherms being 
drawn for differences of 0°-5 F., and are, therefore, 
of an especial distinctness. The smaller charts give 
the lines of equal mean monthly and annual maximum 
and minimum temperatures. The succeeding plates, 
l.-Ixii., are also devoted to temperature, the large 
ones showing the lines of equal diurnal range, the 
small ones the lines of equal absolute maximum and 
minimum values, monthly and annual. The whole 
of these plates, therefore, afford a very complete pic- 
ture of the temperature of India. From the iso- 
thermal charts we can easily follow the warming of 
the Indian land area from south to north-west. In 
February the warm centre, 82°.5, lies under 16° -N. 
(mean); in March, 87°-5, under about 17° N. (the 
middle of the peninsula); in April, 929.5, under 
21° N.; in May the centre, 95°, embraces the whole 
of western India, reaching from 18° to 279 N. In 
June it takes up a position towards the north-west, 
in the Punjab—the Mooltan region—with 97°-5, one 
of the highest monthly temperatures in the world. 
In July the cooling sets in, 95°, and in August it is 
go°, whilst on the Malabar coast, under the influence 
of the rains, the temperature is already down to 77° 
(in 12° to 16° N.). In the northern Punjab, where 
the heat centre lay in June, the temperature sinks to 
55° (down to 52°-5) in January. There also are to 
be found the absolute extremes of the whole of India : 
125° in June and 30° to 25° in January. The daily 
range of temperature varies between 10° on the 
southern coasts and 32°-5 in the north-west. The 
rainy season brings to ne whole country a great 
decrease of the daily range of temperature, from 30° 
and 32°.5 to 15° in Central India. 
Plates Ixiii._Ixxv. show the distribution, monthly 
and annual, of the mean daily relative humidity, the 
two smaller charts on each sheet the distribution at 
8 a.m. and 4 p.m. In the Central Provinces in April 
the atmospheric humidity decreases to 30 per cent. 
in the daily means, and to 20 per cent. at 4 p-m., 
whilst on the coast it is 70 per cent., and in Upper 
