DISTURBANCES AT BOMBAY. 131 



posed to produce them, and into the nature of 

 this cause we ought to enquire. 



The combined influence of temperature, as 

 shewn by the thermometer, and of variable 

 vapour pressure, as ascertained by the dew point, 

 have been supposed sufficient to account for both 

 the daily changes of the wind and of the baro- 

 meter. But I have shewn, in a paper published 

 in the " Philosophical Magazine" for December, 

 1845, that the dew point is not a correct measure 

 of the quantities of aqueous matter that exist in 

 the atmosphere during the different periods of the 

 day ; although there can be no doubt that those 

 quantities do vary, and, in many parts of the 

 world, probably to a greater extent than has been 

 hitherto imagined, though the aqueous matter is 

 not always in the form of vapour. 



Alternating sea and land breezes are, doubt- 

 less, effects of the disturbance of the equilibrium 

 of atmospheric pressure. The air passes from the 

 place where the pressure is greater towards the 

 part where it is less, and this passage of the air 

 constitutes the wind. In the important account 

 of the Meteorology of Bombay, furnished to the 

 British Association at Cambridge, by Colonel 



