1836.] 



of the Wet-bulb Hygrometer. 



423 



with the pressure. On the diagrarh this is very conspicuous in figs. 

 13, 14 ; and as the air approaches dryness, the line formed will be seen 

 amalgamating with the curvature of the former experiments. 

 Tab. IX. — Depressions under increased pressure. 



Barom. 



First Experiment. 



pres- 

 sure, 

 inches. 





Temp. Depres- Hum- 

 air, sicn. idity. 





o o 



30 



93.5 23.5 .24 



33 



— 



36 



21.5 .29 



42 



19.5 .34 



Second Experiment. 



Temp. 



Depres- 



Hum- 



air. 



sion. 



idity. 



o 



o 





93.5 



23.7 



.24 



93.6 



20.9 



.26 



93.8 



17.8 



.29 



94.3 



15.5 



.34 



Third Experiment. 



Temp. Depres- Hum- 

 air, sion. idity. 



o o 



85.0 24.0 .15 



85.2 



14.0 

 11.4 



.18 

 .21 



Fourth experiment. 



Temp. Depres-Hum- 

 air. sion. idity. 



86.4 26.8 .10 



22.8 

 20.7 



.12 

 .14 



In the last experiment the air was maintained for a long time at 

 each pressure, whence its results are perhaps entitled to greater con- 



fidence than the rest. 



The direct theoretical depressions, d x — 



P 

 would be 26°. 8, 22°.3, and 19°. 1, which corrected by the co-efficient 



before found, would become 26°. 8, 25°.6, and 24°. 7 ; these again 

 would have to be diminished for the altered humidity to 26.8, 24*5, 

 and 22.8 ; still, however, differing materially from the experiment, 

 which 1 attribute to the difficulty of keeping up a sufficient draft at 

 the high pressures, in consequence of which the humidity is not fairly 

 estimated. 



If we examine the first experiment we shall have, 



The direct geometrical depressions, 23.5 19.6 16.8 



These modified by co-efficient, .27..,-. 23.5 22.4 21.7 



Corrected to the incipient state of humidity will be, 23.5 20.0 18.1 



The observed depressions being in this case, 23.5 21.5 19.5 



nearly midway between the modified and the corrected numbers, and 

 as much above the latter as they were below them in experiment 

 4, — so it will be not unreasonable to conclude that our formula would 

 hold good for augmented depressions, if proper care were taken in 

 conducting them. 



We have now examined every case of depression that can be ex- 

 perienced in common air, and we may finally sum up this lengthy 

 investigation by uniting the members of the formula, that it may com- 

 prehend both changes of humidity and changes of atmospheric pres- 

 sure thus : — 



d= 84/'—/"+ .27 /A? 

 V " 



The latter member of the equation may be converted into a table 

 of multipliers for heights of the barometer other than 30, which will 

 leave the table I have appended to the present paper applicable to all 



•> 



