ATMOSPHERIC PRESSURE. 



22] 



10 Mt 2 4 G 8 10 N 2 4 6 8 10 

 April 17. 



30.4 

 .3 



1 1 1 1 1 1 1 /'I 1 1 1 1 1 



•'' 1- 



/ \ y a- 



.2 

 .1 



\/ / .4- 



30.0 



29.9 



.8 





1/ b'" 



5 8 





WIND N.E. K WIND 5. W. 



1 1 1 1 1 1 1 1 1 1 1 1 1 



Note on Atmospheric Moisture. 



An attempt was made to obtain the vapor pressure by means of hygrometric observations between 

 February 24 and April 16 ; wet bulb thermometer No. 1644 (covered with a thin coating of ice) was 

 read once or three times a day. Comparing it with No. 3, I find its index correction, from nine 

 comparisons during snow fall, = — 1°.8 at the temperature — 15° Fah. The observations, however, 

 were found too rough, the greatest precision being required at these low temperatures wheu the 

 relative humidity can be determined only approximately, though the numerical amount of vapor 

 pressure (hardly exceeding 0™.02) may be well ascertained. 



The dependence of the atmospheric moisture on the direction of the wind was found by means of 

 tabulation of 128 cases of snow or rain with the direction of the wind. 



During precipitation it blew 56 times from the S. W. ; it was calm 45 times ; and there were but 

 18 entries, mostly in summer, with N. E. wind; "T with S. E., and 2 with W. wind. S. W. is 

 therefore the rainy quarter, as might have been expected, and calms, generally, appear to favor 

 precipitation. 



I 



