1871. ] Proceedings of the Asiatic Society. 15 
tions to the truth, but in order to press on the attention of members 
of the Society the importance of observations of this kind in India. 
He mentioned the part which, according to a very generally re- 
ceived theory, the presence of vapour had in effecting the double 
maximum, and pointed out that this country seemed to afford 
extraordinary opportunity for the complete investigation of this 
subject. 
Col. the Hon’ble R. Strachey begged to differ altogether from 
the views put forward by the President, and characterized the 
doctrine which attributes the daily oscillations of the barometric 
pressure solely to the influence of vapour in the atmosphere as a 
dogma. The actual tension of vapour at any place does not represent 
the portion of the total atmospheric pressure, due to the pressure of 
the vapour, and the difference between the total pressure and the 
vapour tension is not the pressure of the dry air. The very nu- 
merous barometric and hygrometric observations which he (Col. 
Strachey) had made in the plains of India and in the Himalayas, 
up to elevations of between 18 and 19000 feet, speak entirely 
against this view—which he thought had first been put forward by 
General Sabine,—inasmuch as the same fiuctuations in the total pres- 
sure, which are to be observed in the plains, are equally marked at 
high elevations in Tibet, where there is extremely little moisture 
in the atmosphere. Col. Strachey referred to a paper which he 
had published on the subject some years ago in the Proceedings 
of the Royal Society on the distribution of vapour in the atmos- 
phere, in which the data for the above conclusions of his were given 
at length. He said that the day maximum and minimum are un- 
questionably connected with the heating of the air by sun, and can 
be explained by the dispersion of the air over that part of the 
earth’s surface where the temperature is highest, and its accumula- 
tion to the east and west of the most heated area. That this is 
the true cause of the phenomenon is also indicated by the fact, 
proved by observation, that the time of day maximum and mini- 
mum change according to the hour at which the sun rises and sets 
in different localities. The explanation of the nocturnal maxima 
and minima is more difficult, but they are probably secondary results 
of the diurnal changes of temperature. 
