1836.] 



of the Wet-bulb Hygrometer. 



419 



Temp. 



Hyg. 



Temp, of 



wet-bulb, under a 



pressure of 



of air. 

 o 



tens. .0. 22.5 15. 7-5 6.0 5.5 5.0 in. 





o 





o 



o 









84.0 



.18 



61.0 





56-0 



48- 









84.7 



.18 



.. 



, . 



51-0 



. . 









84.4 



.18 



62.0 



57.0 



50-3 



32.0 









87.8 



.18 



64.3 



55.0 



49-0 



35.0 









88.5 



.75 



81.3 



76.4 



69.0 



48.0 





32.0 





92.1 



.12 



64.? 



60.1 



52.9 



31.0 



24.0 



20.0 



18.0 



91.0 



.00 



58.3 



54.4 



48.7 



30.0 



20.4 



18.5 





91.0 



.03? 



, , 



65. 



53.9 



. . 



25.7 



20.0 





93.2 



.05 



79.1 



75.1 



59. f 



. . 



. . 







1 92.0 



.01 



59.5 



63.2 



56.3 



38.5 



• • 



26.4 



20.0 



Tab. VII. — Depressions under diminished pressure. 



1. Expt. with air pump, air 



dried by Sul. Ac. 1.48, 



2. Ditto, corks fitted closer, 



3. Brass tube, better fitted, 



4. Ditto, careful expt 



5. Common air, in Mint vac. 



tube ; dew-point 79°.5, 



6. Partially dried, hair-hyg. 



in balloon av. 34, 



7. Nearly dry air ; hyg. 1°,. 

 1\. Partly dried ; hyg. 12 ? . 



8. Hygrom. variable, av. 29. 



9. Dry air ; hyg. 2°, 



The last experiment is evidently affected with some accidental 

 error, since the depression is less at 22.5 inches than at 30. I ima- 

 gine the external air was admitted through an unobserved leakage of 

 the tube, or a drop of water may have fallen in the tube, and thus 

 moistened the air before it reached the wet-bulb. 



I now detached the gasometer and balloon, and admitted the air of 

 the room directly into the tube at stopcock k (fig. 8) keeping up a pro- 

 longed current at intervals of every two inches of pressure from 30.0 

 upwards to 5 inches, and then descending in the same manner : taking 

 care to wet the thermometer from time to time as its water evaporat- 

 ed. In ascending the scale I regulated the pressures in the barome- 

 ter-gage principally by manoeuvring the stopcock (k') next to the 

 vacuum pipe, the orifice at k remaining constant : whereas in de- 

 scending, I allowed k' to remain untouched while I brought the 

 gage to the desired point by gradually opening the outer stop- 

 cock k. 



The effect of this will be understood on viewing the apparatus : the 



current of air was considerably stronger in the last case than in the 



first, and in consequence the depressions are somewhat greater. To 



this it must be added, that in the ascending scale the depressions 



will tend to lag below their fall amount, while in descending they will 



err in an opposite sense ; all of which is well exhibited in dotted curves 



numbered 10, 11 of diagram 10. The mean of the two series (marked 



by a plain line on the diagram) may be assumed as a good foundation 



for the analysis we have proposed. 



Experiments 10 and 11, on depressions under diminished pressure. 

 Temperature of the room 92°. 2 ; dew-point 74°. 8 = centesimal tension .58 

 Hair-hygrometer, 79 = ditto .57 



3 h 2 



