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



This table commences at four o'clock in the morning, that 

 hour being generally one of the turning-points in the semi- 

 diurnal movements of the barometer. From four to ten that 

 instrument rises from 29*778 to 29852 inches. Now this 

 rise, on the temperature theory, must be considered to have 

 been produced either by a reduction of temperature, as mea- 

 sured by the thermometer near the surface of the earth, or by 

 an increase of the pressure of aqueous vapour, as ascertained 

 by the dew-point; or by both those influences acting together, 

 and producing the rise of the barometer, as a general result. 



We find, however, that during the first two hours, that is 

 from four to six o'clock, the thermometer fell from 78 c *9 to 

 78°*4, being a fall of *5 ; and the tendency of this fall most 

 undoubtedly was to produce a rise of the barometer ; but at 

 the same time the pressure of vapour, as indicated by the 

 dew-point, declined so much as from *761 to "750, or "Oil. 

 Now this comparatively large reduction of vapour pressure is 

 evidently the greater of the two disturbing forces, and the re- 

 sult of the action of both the forces, according to the theory, 

 ought to be a fall of the barometer. But instead of falling the 

 barometer rose during the two hours from 29*778 to 29*805, 

 or *027 ; showing that the movement of that instrument in 

 this time was the reverse of what would have occurred if the 

 temperature theory was true. 



From six to ten o'clock, the remainder of the first period of 

 six hours, the barometer continued rising, and passed from 

 29*805 to 29*852, making a rise in these four hours of '047, 

 whilst the thermometer rose from 7S n, 4 to 81° # 8, or 3°*4, and 

 the dew-point increased from *750 to *771, or *021. Thus of 

 the whole six hours we find that, during the first two, 

 a fall of temperature of . . *5 f* produced a rise of "j ^ 

 and a fall of the dew-point of *0ll\ the barometer ofj 

 which would appear to prove, and as far as the facts given go, 

 do prove, that the small fall of temperature had the greater 

 influence on atmospheric pressure, as the barometer rose *027 

 while both influences were in operation. 



But in the following four hours, from six to ten o'clock, a 

 rise of the thermometer of 3°*4 and a rise of the dew-point of 

 •021, were accompanied by a rise of the barometer of *047 ; or 

 put into tabular form, say that 



a rise of temperature of 3 0, 4 fproduced a rise of~1 . ? 



and of the dew-point of *021 \_ the barometer of J 

 that is between four and six o'clock, when the fall of the dew- 

 point is great compared with the fall of temperature, and the 

 two acting together ought to produce a fall of the barometer, 

 that instrument rises ! But between six and ten the tempera- 



