1836.] 



of the Wet-bulb Hygrometer. 



409 



Tab. III. — Comparison of various formula for the depression of the wet-bulb 

 thermometer in a current of dry air, with the results of experiment. 



<o 



u 





a 

 .2 



CO 

 go 

 <u 

 In 



a. 



CD 



•o 

 u 



V 



to 



XI 



o 





Calculated 



depression for Bar. 30 i 



aches. 





■4J J; 

 ° £ 



| o 

 ns a 



»" « 



<u •- 



s 3 



° S3 



M 



3 X 



t- XI 



V 4 



03 



a 



es 



CI 



CO 



*t« 



> 



u 

 u 



GO 



X 



o 



<6 



"3 



a . 



i- v 



GO 



to °> 



"*> c 



a 



u 



to ^ 



"b •"- 



CCJ ■* 

 W <N 



m o 



3 i 



CO p 



© 



CO 



P t~ 



a« 



u " 



•s* 



CI 



to — • 

 "p,° 



Sri 



"5 a 



P- 



Herbert's formula 

 D 1-23 3 =i56.s/> 

 (nearly.) 



cs r> 

 "3 >> 



a"S 

 s S 



CO ^ 



a SS 



5 II 



5 « 



"p 



a 



1m 



1" 



o 



u 



Cl, 

 O 



ra 



a! 



to ^ 



It H 



s-s« 



fa 



a 



o 



o a 

 S 2 



<*« > 

 o >- 



U 

 t- CO 



2-° 



w 



< 



ti 



D 





D 



o 



D 



D 



D 



D 



D 





a 

 30 







20.8 



9.2 



G. 



H.7 



9.2 



8.6 



11.0 





10.8 



10.6 





40 



27.3 



12.7 



G. 



14.9 



13.1 



12.4 



13.5 





14.0 



13.6 





50 { 



33.9 

 33.0 



16.1 

 17.0 



G. i 

 A. f 



18.6 



16.4 



16.4 



16.7 



•• 



17.6 



17.1 



+0.1 



60 { 



40.1 

 38.4 



19.9 

 21.6 



G. "I 

 A. / 



22.9 



20.6 



20.7 



20.0 



23.4 



21.8 



21.3 



—0.3 



'»{ 



46.0 

 44.9 



23.7 

 25.7 



?:} 



27.6 



24.9 



25.2 



24.1 



28.1 



26.4 



25.9 



+0.2 



80 



. . 



30.6 



p. 



32.7 



29.7 



29.9 



28.4 



33.2 



31.3 



30.8 



+0.2 



90 





, 



35.5 



p. 



38.2 



34.6 



34.7 



33.1 



38.4 



36.5 



36.0 



+0.5 



100 





. 



40.8 



p. 



44.0 



40.0 



39.7 



38.2 



44.0 



42.2 



41.6 



+0.8 



110 





. 



47.8 



s. 



50.0 



46.0 



44.9 



43.5 



49. C 



48.3 



47.6 



—0.2 ? 



120 





. 



54.1 



s. 



56.4 



52.0 



50.2 



49.2 



56.0 



54.5 



53.9 



—0.2 ? 



130 





, 



60.9 



s. 



63.1 



58.6 



55.6 



55.1 



62.2 



61.1 



60.5 



—0-4 ? 



140 





, # 



68.2 



s. 



70.0 



65.5 



61.0 



61.3 



. . 



68.0 



67.3 



—0.9 ? 



150 





t , 



74.8 



c. 



.. 



72.4 



66.7 



, . 



. . 



75.1 



74.3 



—0.5 



160 





t m 



81.3 



H. 





79.4 



72.5 



. . 





82.3 



81.5 



+0.2 



170 



80.0 



90.0 



P. 





87.0 



78.2 



79.8 



90.4 



89.6 



88.9 



—0.1 



ISO 



80.4 



99.6? 



P. 





94.6 



84.2 



.. 





97.2 



96.5 



-3.1? 



190 



85.0 



105.0 



P. 



107.0 



102.0 



91.2 



98. 



102.0 



105.0 



104.3 



—0.7 



200 



. , 



, , 



, , 



. . 



109.5 



96.4 



, . 



. . 



112.0 



111.1 





210 



, . 



. , 



, , 



. . 





102.4 



, , 





120.0 



118. 





? 



1 



45.0 



.. 



P. 



627. 



625 





105. 



308. 



487. 



567. 



552. 





[The letters in column 4 denote, G. Gay Lussac ; A. Apjohn ; P. Prinsep ; 

 S. experiments tried at Benares, by suspending the wet-bulb thermometer in a half 

 filled bottle of sulphuric acid ; these have been augmented 10 percent, on insertion : — 

 C and H. Carbonic acid and Hydrogen gas heated in the steam pipe.] 



The last line may be looked upon, in some measure, as the test line 

 of the various formulae : for, the hot current of air from the furnace, we 

 have seen, barely melted lead and boiled mercury ; its temperature, 

 therefore, could not much exceed 660 Farh. Let us see what it would be 

 according to the principal formula? depending upon the aqueous tension 

 at V, which, when t' = 145° is 6.53 inches by Dalton. 



Leslie's formula gives 6.53 X 96 + 145 = 772* 

 Gat Lussac's (retaining/) 6.53 x 95.7 + 145 = 770 

 (omitting— /' in divisor) 6.53 X 782 + 145 = 655 

 Hudson's formula gives 487 + 1 145 = 632 



Apjohn's, 6.53 X 87 + 145 = 702 



Formula deduced from my expts. 6.53 X 84 + 145 = 697 

 Anderson's, Herbert's, and my former formulae are too much at 

 variance at this high point to be worthy of quotation. The rest 



3 G 



