248 Mr. T. Hopkins on the Hourly Alterations of 



Table of the Mean Hourly state of the following instruments, '« 

 and of the force of evaporation for the four winter months 

 of 1843. 



By examining this table we may see that evaporation at four 

 in the morning is 6°*5, from which it rises, until at ten o'clock 

 it is 9"'3, being an increase of 2°"8; and during this time the 

 barometer is admitted to be raised to the height that it attains, 

 29*928 inches, through the pressure of the vapour that has 

 been recently produced by evaporation and thrown into the 

 atmosphere. 



From ten to twelve o'clock, evaporation, as measured by the 

 difference between the two thermometers, increases up to 1 1'^'S, 

 being a further rise of 2°; but at the same time the barometer, 

 instead of rising higher, as might be expected, falls no less 

 than •044, as by that hour it sinks to 29"884 inches. 



Evaporation becomes rather less active after twelve o'clock ; 

 but it still shows great force, and continues to exhibit it till 

 four o'clock, at which time it is 9°-l, being only -2 less than 

 it was at ten in the morning. Yet during the whole of the 

 time from ten in the morning to four in the afternoon, when 

 evaporation was so energetic, the barometer was falling, and 

 sunk no less than -llS. What then became of the vapour 



