416 



Experimental Researches on the Depressions [July, 



July and 

 August 



r 1823 80.5 



1824 85.6 



1825 86.9 



1826 84.4 



78.2 

 82.1 

 81.3 

 80.8 



2.3 

 3.5 



4.6 

 3.6 



2.3 

 2.6 

 4.4 

 3.6 



Means 84.4 80.6 3.8 



Decem- 

 ber and 

 January, 



ri823 

 1824 

 1825 

 1826 



60.1 

 61.8 

 63.5 

 63.8 



55.7 

 56.6 

 58.3 

 54.9 



4.4 



5.2 

 5.2 

 8.9 



3.2 0.107 



2.3 

 4.0 

 5.6 

 3.1 



Means 62.3 

 The f 



whole 

 twelve 

 months, 



1823 76.4 



1824 80.0 



1825 80.0 



56.3 



68.1 

 71.2 

 71.1 



6.0 



8.3 

 8.8 

 8.9 



2.5 



per. an. 



65.6 

 60.5 

 67.1 



0.085 



Means 78.9 70.1 



8.7 



64.4 

 5.37 



0.179 



f d*f> 



dxf 



34 



1.020 3.88 0.114 



0.462 2.77 0.681 



0.729 6.34 0.186 



permonth 



I have, as yet, had no opportunity of applying the principle ascer- 

 tained from this table, to the circumstances of other places*. 

 § 3. — -Influence of the Barometer on the Wet-bulb depression. 

 All philosophers agree in rating the influence of atmospheric pres- 

 sure on depression as inversely proportional to the height of the 

 barometer ; so that when the depression under a pressure of 30 



inches is known, it may immediately found for any other pressure by 



30 

 multiplying d into — > p being the observed height of the barometer. 



That the evaporation increases with diminution of pressure nearly 

 in the above ratio, has been proved by various experiments ; and it 

 might confidently be anticipated, from the necessary connection be- 

 tween the evaporation and the refrigeration, (as exemplified in the 

 concluding table of my last section,) that the same law would prevail 

 in the depressions : but the only two experiments directed to this 

 point that I am acquainted with, lead to an opposite conclusion. 

 These were cited in my former paper : but as they are not accessible to 

 many readers, I will here repeat them. Mr. Daniell's experiment 

 will be found in Jour. Roy. Inst. XVII., and Mr. Anderson's in 

 Brewster's Cyclopedia, Art. Hygrometry. 



Barometric 

 pressure. 



30.4 



15.2 



7.6 



3.8 



1.9 



.9 



.5 



* The tables now published by the astronomer at Madras will afford good 

 data ; but his mode of measurement must be first known, as his evaporations 

 seem double of my own. 





Evaporation 



Depression 



Incre- 



Depression 



Incre- 



itio. 



in grains by 



of wet-bulb 



ment. 



of wet-bulb 



ment. 





Daniell. 



by Daniell. 





by Anderson. 





1 



1.24 



9 







5 







5 



2.97 



12 



+3 



9 



+* 



* 



5.68 



15 



+3 



13 



+4 



i 



9-12 



18 



+3 



18 



+5 



1 6 



15.92 



21 



+3 







1 



T5 



29.33 



24.5 



+3.5 







1 



6 4 



50.74 



26 



+ 1.5 







