24-6 Mr. T. Hopkins on the Hourly Alterations of 



the reasons therein contained, and his determination to adopt 

 the name of Neptune. Prof. Gauss and Prof. Encke have 

 also, as I understand, adopted this name. I have only to add 

 that it is my intention (and I am permitted to say, the inten- 

 tion of INIr. Adams also) to follow the example set by these 

 eminent astronomers. 



Cambridge Observatory, 

 March 22, 1847. 



XL. On the Hourly Alterations of the Vapour Atmosphere at 



Bombay, By Thomas Hopkins, Esq.* 



[With a Plate.] 



I HAVE already availed myself of the observations made 

 at Bombay under the superintendence of Dr. Buist, 

 through a paper on the meteorology of that place by Colonel 

 Sabine, on which I made some remarks that were inserted in 

 the Philosophical Magazine for December 184'6. But since 

 those remarks were written I have had ti'ansmitted to me, 

 through the kindness of Colonel Sykes, a lithographed copy 

 of the observations themselves, in which are to be found im- 

 portant facts connected with the hourly production of aqueous 

 vapour at Bombay, and its apparent influence on the move- 

 ments of the barometer. 



In addition to the hourly registrations of other meteorolo- 

 gical instruments. Dr. Buist has furnished columns of the 

 heights of the wet- and dry-bulb thermometers, showing the 

 hourly depi'ession of the wet below the dry thermometer for 

 each month of the year 1843. From these columns, it appears 

 that the wet was depressed below the dry instrument, to a cer- 

 tain extent varying both with the time of the day and the 

 season of the year. The depression was the least in the wet 

 season and the greatest in the dry one; and, with reference to 

 tlie diurnal changes, the depression was generally, but not 

 uniformly, the least about sun-rise and the greatest near to 

 mid-day. These depressions of the wet below the dry ther- 

 mometer are known to be results of the cooling power of eva- 

 poration of water on the bulb of the wet instrument ; and the 

 cooling thus produced is proportioned to the extent of eva- 

 poration of water that takes place ; being small when the eva- 

 poration is little, and great when it is much. Thus the regis- 

 tration of the wet-bulb thermometer not only furnishes us 

 with means of determining how far evaporation kept down the 

 temperature of the thermometer exposed to its influence, but 



* Coinnuinicated by the Author. 



