348 MR. S. A. HILL OH THE WINDS OF NORTHERN INDIA, AND THEIR 
North-Western 
Central India 
Himalava. 
' 
and Ilajpu’ana. 
O 
O 
Sea-level to 1000 feet . 
4T1 
2-84 
1000 „ 2000 „ . . . 
3-96 
325 
2000 „ 3000 „ . . . 
379 
3-66 
3000 „ 4000 „ . . . 
3-61 
4-06 
When allowance is made for the decrease of diurnal range on ascending, these 
o o 7 
rates become, for the maxima— 
North-Western 
Central India 
Himalaya. 
and Raj putana. 
Sea-level to 1000 feet . 
O 
6-5 
6-2 
1000 „ 2000 „ . . . 
5-0 
61 
2000 „ 3000 „ . . . 
4-0 
6-0 
3000 „ 4000 „ . . . 
35 
5-8 
Such very rapid rates for Central India are partly confirmed by observations made 
during the present year (1886) in a tower at Allahabad, which for April and May 
give initial rates of decrement of 40° and 37'5° per thousand feet respectively at the 
time of diurnal maximum. 
According to the law of decrement deduced from the last Table, the topsy-turvy 
movements described by Chambers would, at the hottest time of the day, ascend the 
slopes of the North-Western Himalaya to an elevation of some 2600 feet; while, over 
the mountain tops of Central India and Rajputana, they would rise to above 11,000 
feet, if the same law of temperature decrement held good.* 
The heights thus computed, of course, have no pretension to exactness ; in fact, the 
former is undoubtedly too low, for the temperature decreases much less rapidly on a 
broad mountain zone heated by the sun than it does in the free atmosphere. They 
suffice, however, to show that about midday, in the hot season, convective currents are 
very active up to an altitude of several thousand feet over the drier part of Northern 
and Central India. It is probable, therefore, that the wind direction anomalies, which 
are so striking at this season, may be explained by the descent, from a considerable 
height, of atmospheric strata which retain, for a time, the velocity acquired by them 
under the pressure differences prevailing at the level from which they descend. 
* The temperature of tlie Himalayan slope may be represented by tlie formula t = T — 7'5 7t 
+ 1-0 7r - 0-08 fc®, while according to the ultimate law of convection t = T — 5’46 7t; T being’ the sea- 
level temperature and h the height expressed in thousands of feet. Equating these, we get h — 2560 feet. 
For Central India and Raj putana, the formula best expressing the results in the Table is t — T — 6’3 h 
+ O'l h", from which we find the height, where the temperature would be the same as that given by the 
law of convective equilibrium, to be 11,330 feet. 
