RECORD AND DISCUSSION OF ATMOSPHERIC PRESSURE. lU 



ing, each fall uf snow. If snow fell for less than three consecutive hours, I have 

 taken no notice of it in this investigation. The mean result from 563 hours of 

 comparison, gave only a diflierence of 0.006 inch, hy which quantity the barometer 

 is lower during the fiill of snow than otherwise. 



Variabilifi/ of Atmospheric Pressure icith the Direction of the Wind. — The connec- 

 tion of the atmospheric weight with the direction of the wind requires, in oi'der to 

 find its average effect, a great number of observations, particularly on account of 

 the irregular oscillations of the barometer in the winter months. The following 

 results are derived from a comparison of the barometric readings at the hours 6 

 A. M., noon, G P. M., and midnight, for each day, with the respective mean monthly 

 reading during 17 months of observations. These difference were then arranged 

 according to the directions of the wind. The result is as follows (+ indicating 



f above | ,, n 



-^ } the mean) : — 



(. below J 



Magnetic direction. Inch. 



N —0.022 



N. E. . . . +0.072] On account of the comparatively small number of observations for 



E. . . . . — 0. lOOi these direction.s, they may be combined : E. N. E. — 0.044 in. 

 S. E. . . . 0.000 



S +0.038 



S.W. . . . +0.045 



W —0.0.31 



N. W. . . . —0.0.31 



From 1050 comparisons of calms and ijarometric readings, the latter -were found 0.005 inch above 

 their mean value. 



It is only during S. and S. W. (magnetic) winds that the barometer rises above 

 the mean value; during all other winds it is dejiressed. 



Relation of the Atmospheric Pressure to each Wind and to the Temperature of the 

 same. — To show this dependence, it is best to put the relation of the atmospheric 

 pressure, as well as that of the temperature, to the winds, in an analytical form. 

 In my discussion of the obsei'ved temperatures at Van Rensselaer Harbor, a table 

 was made out showing the dependence of the temperature on the direction of the 

 wind. If we deduct the mean elevation of temperature by the winds from each 

 separately, we obtain the following table of the effect of each wind on the tem- 

 perature (+ indicating an < . > of temperature) : — 



(. depression J 



Magnetic direction. 



N. 



N. E. 

 E. 

 S. E. 



+ 0°.6 

 +0.4 

 + 0.1 

 —1.4 



Counting from the north (or belonging to a (magnetic) north wind) round by 

 E. to 360°, we obtain, by using Bessel's formula, 



r= +1°. 02 sin (0 + 286°); 

 or, for the true directions, 



T= +1°. 02 sin (0 + 34°); 



and similarly, from the barometric relation to the winds, 



B= +0.01Sin. sin (0 + 354°). 



