Mr. T. Hopkins on the Meteorology of Bombay. 473 



with the hottest hours of the day." But the Colonel after- 

 wards shows from other accounts, that there is a very small 

 morning maximum in the locality named, which occurs between 

 the hours of eight and eleven a.m. This he attributes to the 

 pressure of additional aqueous vapour, and he seems to think, 

 such a fact confirmatory of the correctness of his views. If 

 however an increase of vapour up to eleven o'clock could 

 raise the barometer, why should not that instrument rise fur- 

 ther after that hour? Had we a registration of the wet and 

 dry-bulb thermometers and of the dew-point, it is to be pre- 

 sumed that proof would be furnished that evaporation was 

 more active after eleven than it had been before that hour, 

 and that there was no decline of the dew-point until a much 

 later period of the day. The vapour that must be presumed 

 to have passed into the atmosphere in the hottest part of the 

 day, must either have added to the previous pressure on the 

 barometer and raised it, or it must have been condensed, and 

 warmed the higher part of the atmosphere. As it did not 

 produce the former effect, in the absence of information we 

 may assume that it produced the latter. 



In the extract given from M. Dove's communication we 

 have no account of the daily range of the barometer, or of the 

 extent of its fall during the day, though that is the most inter- 

 esting fact to be ascertained; this is to be regretted. If a 

 sun-heated surface is the cause of the atmosphere becoming 

 so much lighter in the day than it is in the night, the atmo- 

 sphere at the places named by M. Dove ought to be rendered 

 much lighter every day than it was in the previous night, 

 seeing that the temperature of the day is raised greatly above 

 that of the night ; the daily range of the barometer should 

 consequently, on the Colonel's theory, be extensive. Is it so? 

 If it is not, it is so far evidence against the tht^y. 



It is stated in the Russian account that in the places pointed 

 out there is one maximum and one minimum, the maximum 

 nearly coinciding with the coldest, and the minimum with the 

 hottest hours of the day. And the conclusion drawn seems to 

 be, that alteration of surface temperature is the sole cause of 

 the movement of the barometer : hence the desirableness of 

 showing the extent of that movement. If it be great, it will 

 so far show that the heating of the surface of the earth by the 

 sun could materially diminish atmospheric pressure. But if 

 the daily movement of the barometer is found to be small, it 

 will present presumptive evidence that daily surface-heating 

 has no important local effect on the weight of the atmosphere. 

 A full account of the registrations in this part of the world 



Phil. Mao-. S. 3. Vol. 29. No. 196. Dec. 1846. 2 K 



