the Vapour Atmosphere at Bombay. 251 



increasing in quantity and accumulating in the atmosphere ; 

 and as far as that matter influenced the atmosphere, it must 

 have increased its weight. The aggregate pressure of aqueous 

 matter did not cease to increase at ten o'clock in the morning, 

 when the barometer began to fall; that fall was produced by 

 a new cause which then came into operation in the locality, 

 namely, the expanding and displacing power of liberated 

 lieat. 



It will probably be asked whether cloud forms near to, or 

 over Bombay, after ten o'clock, and increases till four, as 

 assumed ? and to this inquiry I cannot give an answer that is 

 likely to be quite satisfactory, not having full information on 

 the subject. Dr. Buist, in his introductory remarks, does not 

 particularly notice the formation of clouds within that portion 

 of the day. In the hourly-observation tables there is a column 

 for describing the appearance of clouds ; and the entries in 

 that column show that the cumulus, the cirro-cumulus, and 

 the cirro-stratus were often formed, but they are not de- 

 scribed in such a way as would justify me in adducing them 

 as proofs of the agency here ascribed to them, althou^^h they 

 do furnish rather strong presumptive evidence on the subject. 



Clouds ibrm pretty freely from ten in the morning till four 

 in the afternoon, whilst from ten at night to four in the morn- 

 ing the atmosphere is represented as being generally clear : 

 and taking the accounts given of the clouds during the two 

 periods, we are fully authorized to say that they formed and 

 remained suspended in the air during the former period, and 

 were dissolved before the arrival of the latter period ; showing 

 that there were daily formation of cloud by condensation of 

 vapour, and daily dissipation of those clouds by evaporation. 



But in addition to the daily formation of visible clouds, there 

 are indications that condensation takes place, but only to such 

 an extent as to produce a haziness or misty appearance in the 

 sky; and if this process is carried on until a considerable 

 height is attained, it must warm the atmospheric mass and 

 lighten it. Indeed, at the commencement of the process of 

 gradual condensation, the cloud that is thereby formed is not 

 seen ; as it is only when a suflicient stratum of floating glo- 

 bules of water is produced that the cloud becomes visible. 

 The first slight falling of the barometer before rain is probably 

 caused in this way. 



Judging from analogous cases, it may be presumed that 

 palpable dfiily clouds at Bombay were first formed near the 

 high ground to the cast of that place, as such clouds in other 

 similar places generally foruj near to, or against the sides of 

 hills. Our old navianlors have described such formations in 



