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



conclusively, that the fluctuations of the barometer in the 

 times named were not produced by alterations of temperature 

 and of vapour pressure, as they are exhibited to us by the 

 thermometer and the dew-point. 



It should be borne in mind, that it is the fall of the baro- 

 meter from ten in the morning to four in the afternoon while 

 evaporation, as shown by the wet-bulb thermometer, is active, 

 for which we have particularly to account. Temperature 

 rises while vapour augments up to ten o'clock in the morning, 

 and at the same tir. .e the barometer rises ; but after ten, though 

 the same two causes continue in operation, yet the barometer 

 falls, and continues falling until four in the afternoon. Now 

 why should the same causes be supposed to produce one effect 

 up to ten o'clock, and another, of an opposite character, for 

 six hours after that time ? This is the question that has to be 

 answered. The temperature theory, so far from accounting 

 for the occurrence of these phenomena, is directly opposed to 

 them, and utterly fails to account for the fall of the barometer 

 from ten to four o'clock. 



The alterations which took place in the subsequent twelve 

 hours present additional evidence of the inadequacy of the 

 temperature theory to account for the semi-diurnal fluctuations 

 of the barometer ; but as they are not equally palpable with 

 those already examined, it is unnecessary to go into a consi- 

 deration of them. 



In furnishing such accounts as those of the meteorology of 

 Bombay, that which is required in order more fully to eluci- 

 date the subject is, that in addition to the usual registrations 

 the temperature of the wet-bulb thermometer should be given. 

 This would enable us to trace the vapour that is thrown by 

 evaporation into the atmosphere in the hottest part of the day. 

 Could we do tW*% there seems no doubt that it would be found 

 ascending in the atmosphere until it became condensed and 

 formed cloud ; and the heat liberated by this condensation, 

 as I have elsewhere explained, is the real cause of the dimi- 

 nished pressure of the atmosphere in the locality during the 

 six hours that the barometer falls. 



In a note appended to the paper published in the Philoso- 

 phical Magazine for January 1846, Colonel Sabine gives an 

 extract from a paper received from M. Dove, which is stated 

 to have been read in the Academy at Berlin, in which it is said 

 that "at Catherinenbourg and Nertchinsk, on the mean of 

 several years, and at Barnaoul, in the years 1838 and 1840, 

 the mean diurnal barometric curve itself exhibits but one 

 maximum and one minimum in the twenty-four hours ; the 

 maximum coinciding nearly with the coldest and the minimum 



