19, 4 Reinking and Groff: Siamese Seedless Pummelo 895 
The temperature of Siam, though the country lies entirely within the 
northern tropic, is considerably effected by peculiar local conditions and 
therefore varies very perceptibly in different localities. On the plains of 
Central Siam, between the months of February or March and October, 
the sea wind blows from the south or southwest almost continuously, 
mitigating the heat of the days and rendering the nights comparatively 
cool. During this period, which comprises the hot and the rainy seasons, the 
temperature rarely raises above 98° fahr. or falls below 79° fahr. From 
the end of October to February, the so-called cold season, the wind blows 
from the northeast when the maximum temperature may reach 92° fahr. 
and the minimum fall as low as 54° fahr. Formerly the climate of Bangkok 
city was very similar to that of the surrounding plains but during the 
past few years a change has become noticeable. Sir John Bowring in 
his book on Siam, gives statistics of the temperature of Bangkok over 
the period 1840 to 1847, during which the maximum temperature regis- 
tered was 97° fahr. and the minimum 54° fahr. Observations of a 
much later date give results very similar to the above but the statistics 
of the last ten years or so show an almost continual increase in the average 
daily range and at the present time, while the minimum temperature remains 
much as it used to be, the maximum reaches 105° or 106° fahr. each year 
during the hot weather and 100° fahr. during almost every month of the 
other seasons. The causes of this climatic change have not hitherto 
been explained but it is possible that they may be found in increase of 
population, in the substitution of bricks and tiles for timber and thatch as 
house building materials, or in the draining of marshes in and around 
the city. 
In Central, Northern, and Eastern Siam there are three distinct sea- 
sons, the hot weather, the rains, and the cold weather. The first extends 
from February, or March to May, the second from June to October, and 
the third covers the remaining four months of the year. When the 
northeast winds blow strong, the cold weather is very marked and, though 
the actual temperature is not below the average summer heat of Europe, 
causes some inconvenience to the people of the country. At times, however, 
the seasonal winds fail and when this happens the cold weather is 
scarcely to be distinguished from the hot. ; 
The statistical yearbook of the Kingdom of Siam for 1919 ° 
gives the following monthly meteorological reports, Tables 1, 2, 
and 3, on the mean temperature, the mean daily range, and the 
mean solar radiation, for ten years, from 1909 to 1918. These 
reports for Bangkok will give some indication of the temperature 
in the Nakorn Chaisri region, even though this region is some- 
what removed. 
* Statistical year book of the Kingdom of Siam, 1919. Fourth number. 
Published by the Department of Commerce and Statistics. Ministry of 
Finance. English Edition. December, 1919. 
