44.6- REPORT—1904. 
pressure and other conditions are slowly established in Southern Asia, which 
directly contribute to the advance of the monsoon winds over the Indian seas, 
but which in no way assist the preliminary burst across the equator, the first stage 
towards the establishment of the south-west monsoon circulation. 
This preliminary period is the hot-weather season, lasting from about the 
middle of March to the middle of June (on the average in Northern India), 
During this period temperature increases rapidly until the last week in May or 
first week of June, when maximum day temperatures ranging between 120° and 
125° are usually recorded in the driest and hottest interior districts of Northern 
and Central India. Pressure decreases part passu in the heated land areas of 
Southern Asia, which become areas of low pressure and indraught relative to the 
neighbouring seas. The indraught only extends to a comparatively short distance 
landwards and seawards from the coasts, more especially in the larger sea area, 
the Arabian Sea, over the centre of which light variable or northerly winds obtain 
even immediately before the advance of the monsoon currents. In the interior of 
Northern and in Central India exceedingly dry and hot westerly winds prevail 
with great steadiness. 
The weather in India during this period depends almost entirely upon local 
thermal actions and contrasts of temperature and humidity conditions. Skies are 
generally free from cloud, but the air is more or less charged with dust and is 
excessively dry (humidities of 1 to 5 being of occasional occurrence in North- 
western India). 
The characteristic features of the dry season are hence most strikingly exhibited 
immediately before the advent of the wet monsoon. There is no gradual change 
over the greater part of India from one to the other such as would occur if the 
furnace, or Central Asia hot area, theory were correct. Over small isolated 
portions of India, including Tenasserim, Arakan, Lower Burma, Assam, Bengal, 
and Malabar, thunderstorms giving more or less heavy downpours occur in 
increasing frequency during the period. The rainfall is considerable to large in 
amount in these areas, and is of much agricultural value in some districts—e.g., in 
Assam for the tea crop. In those areas the transition to the rainy season is much 
less abrupt and spasmodic, the chief differences being that the rainfall in the wet 
season is more general and frequent, larger in amount, and rarely accompanies 
thunderstorms. 
The transformation from the hot weather to the rains is usually effected between 
the 1st and 15th of June. It commences in the equatorial belt with a consider- 
able increase of pressure and air movement accompanying a strong rush of 
southerly winds, the continuation of south-east trade winds, across the equator. 
If the burst be sufficiently strong the rush is continued northwards over the 
Indian seas as a wave of disturbance, squally weather, heavy rain, and much 
violent electric discharge or action, invading areas characterised previously by 
light and variable winds and fine weather. The disturbance usually increases 
with its northward advance, and frequently, when it reaches lat. 12° to 16° N., it 
concentrates into a cyclonic storm. Such a storm almost invariably marks the 
commencement of the monsoon in the Bay of Bengal, and in about two out of 
five years in the Arabian Sea. The advancing humid currents in the rear of these 
initial cyclonic storms or waves of disturbance march over the sea areas in a few 
days, and thence cross the coasts towards which they are determined by the low- 
pressure regions in the land areas of Southern Asia, where they produce an almost 
complete reversal or transformation of the weather conditions, the result of which 
is that moderately high temperature and small diurnal range of temperature, great 
humidity frequently approaching saturation, much cloud, and frequent rain obtain 
for the next three months over the greater part of India, until, in fact, the middle 
or end of September. 
The reverse change—viz., the withdrawal of the humid south-west currents— 
then commences, and is a slow process, requiring usually from two to three months 
for its completion. 
This is due to a gradual decrease of strength, and hence to a fairly continuous 
contraction of the field of the current, and also of its elevation or thickness. The 
