DISTURBANCES AT BOMBAY. 139 



reaches its maximum. While, however, the land 

 breeze is thus blowing from eleven at night to 

 four in the morning, and seeming to indicate that 

 the air is becoming heavier over the land, the 

 barometer on the land at Bombay is not rising, 

 as might be expected, but on the contrary is 

 falling. Now that this fall is not attributable 

 to an increase of temperature is clear, as during 

 the time the thermometer is sinking ! And that 

 it is not due to a general diminution of atmo- 

 spheric pressure is to be presumed, because the 

 land breeze shows that that pressure is increasing 

 over the land ! What, then, is the cause of this 

 fall of the barometer ? It is, apparently, the 

 reduction, not of general atmospheric pressure, 

 but of separate vapour pressure through the 

 deposition of dew. 



From ten at night to five in the morning, the 

 period now under consideration, radiation of heat 

 cools the surface of the earth, and that part of the 

 atmosphere which is near to it, sufficiently to 

 condense a part of its vapour, without thereby 

 raising the temperature, as the cooling effect of 

 radiation is greater than the heating influence of 

 condensation of vapour, and the results are the 

 deposition of dew and the reduction of vapour 



