Jaxuaky 10, 1907 | 
NATURE 243 
Assam 80 per cent. On the west coast during the 
rainy season it is 90 per cent.; in the Punjab 50 per 
cent. to 60 per cent. In similar manner Plates Ixxvi.— 
Ixxxvili. show the mean distribution of 
vapour, monthly and annual, and at 8 a.m. and 
4 p-m., the changes are mostly the reverse of those 
of relative humidity. The mean vapour pressure 
reaches inch 0-95 inch on the and 
over the Bay of Bengal in May, while in January it 
is only 0-40 inch over the land. The rainy season 
brings to the whole peninsula a high vapour pressure, 
but on account of the decrease of temperature it is 
generally not higher than 0.85 inch; only in the 
lower and middle Ganges valley is it 0-95 inch. The 
daily variations of the relative as well as of the 
absolute humidity are very great in the dry season. 
The charts exhibiting the distribution of humidity 
are followed by Plates Ixxxix.-ci., showing the mean 
daily cloud distribution. Here also we find smaller 
charts representing the cloudiness at 8 a.m. and 
4 p-m. Such an exhaustive picture of cloudiness as 
we have presented to us in these Indian charts did 
not hitherto exist for any part of the world. The 
difference in the cloudiness in various parts of India 
in the several seasons is very great. In the middle 
Indus valley we find a mean cloudiness of 1.5, in 
Upper Assam of 6.0—these are the extremes in the 
annual means. In June the Punjab has still only 
1.0, the Malabar coast and Assam 8.0, in western 
Bengal even g-0. In October the minimum, o.5, lies 
in the Punjab, the maximum, 8.0, in southern Deccan. 
The technical finish of these maps especially 
beautiful and impressive. 
We now come to the concluding series, Plates cii.— 
eXx., representing the rainfall conditions. The prin- 
cipal charts, monthly and annual, show the rainfall 
distribution by means of isohyets;' the smaller ones 
give the lines of equal mean number of rainy days 
and the storm tracks for 1876-1901. Until now no 
monthly rainfall charts for India had been in exist- 
ence. H. Blanford had added to his great work on 
the rainfall of India (‘‘ Memoirs,’’ vol. iii.) merely 
an annual chart. The principal areas of rainfall in 
India—the Malabar coast and the Khasi Hills of 
Assam, with from 200 inches to 450 inches of rain 
annually—are generally well known; but what we re- 
gard as the most extensive rain region is the Malabar 
coast rather than the Khasi Hills, as is especially evi- 
dent from the June and July charts. On the Malabar 
coast in July we find a long area with 50 inches of 
rain, whereas the Khasi Hills have only the isohyet of 
20 inches (Cherrapunjee omitted). In June both regions 
have isohyets of 30 inches. The driest region is in the 
lower Indus valley (round the hottest place in India 
Jacobabad), with an annual total of only 5 inches. 
The mean values of the number of rainy days lie 
between the limits of to on the lower Indus, 125 on 
aqueous 
0-90 to coasts 
is 
the Malabar coast (Cochin) and in Assam, and 200 
in the south-west part of Ceylon. The isohyets are 
also drawn for the seasons—for January and 
February, March to May, June to October, and 
November and December (the main annual Indian 
seasons), and also for the combined results for 
NO. 1941, VOL. 75] 
December to April and for May to November. The 
smaller charts show the number of rainy days, and 
for January, May, July, and October the midday 
isobars at an elevation of 10,000 feet. On the chart 
for January and February appear the welcome rains 
of and north-western, India, 
northern, especially 
shown by isohyets of from 2 inches to 5 inches; on 
the March to May chart the spring rains in Assam, 
from 20 inches to 30 inches, and on the west coast of 
Ceylon, 20 inches, are particularly noticeable. 
Of special interest are fifteen smaller charts giving 
In 
we 
the storm and cyclone tracks (period 1876-1901). 
the winter half of the year, the cool 
find the storm tracks (paths of the 
in north India, mostly north of 24° N. First, in 
November there two, thirteen 
storms in the direction from the lower Indus towards 
the Ganges delta. In January there more 
than thirty northward of 24° N., while there are 
only four southward to 20° N. In February they 
still remain in northern latitudes; we see two main 
paths with twenty-five tracks—in March not more 
than twelve. This seems to be the end of the period 
of winter storms in north India. On the April chart 
we already find the tracks of four great cyclones over 
the Bay of Bengal, the Arabian Sea, and from the 
latter two advancing towards north-western India. 
To the cyclone tracks are attached the dates, so that 
the direction and velocity can be ascertained, but with 
the storm tracks we miss an indication of the direc- 
tion of movement of the depressions (say by means of 
an arrow). We certainly know that in the winter 
half-year in northern India these tracks are generally 
directed from west to east, but as we proceed through 
the year there are doubtful cases, as the summer de- 
pressions from the Bay up to the Ganges valley and 
westward towards Central India. In May, and again 
in October and November, we find numerous tracks 
over the Bay; in November also over the Arabian 
Sea. In this month two cyclones crossed the penin- 
sula, and, therefore, the Ghats, from the Bay to the 
Arabian Sea (between 12° and 14° N.)—rare cases. 
In December only one great cyclone moved up the 
Bay from south to north, and some smaller ones from 
east to west. During the rainy season (June to 
September) the upper north-west corner of the Bay 
becomes the birthplace of numerous depressions, 
which pass into the country. In September this 
“area of cyclonic storm generation ’’ extends further 
south to 15° N., and also goes further into the Bay. 
These are the storms which carry the rains of the 
Ganges valley upwards and over Central India. 
During the months of June to August it appears that 
even on the land depressions are developed which go 
westward (direction of movement wanting) as far as 
the Indus. Three.small charts show these land- 
formed storm tracks (period 1886-1900). 
We now conclude our cursory examination of the 
very richly-stored volume of charts lying before us, 
for which science as well as practice, so long as they 
have to depend upon climatic factors, are indebted 
to the Indian Government. Sir John Eliot, the 
author of this work, has produced a worthy monu- 
season, 
depressions) 
are in December 
are 
” 
