AMERICAN JOURNAL OF SCIENCE. 
[THIRD SERIES.] 
[Read before the National Academy of Sciences, New York, Oct. 28, 1879.] 
Mean pressure of the Atmosphere over the United States at differ- 
ent seasons of the year. 
With serious difficulties, a part of which have resulted from the 
mode in which the barometric observations at the mountain 
stations of the United States Signal Service are reduced to the 
evel of the sea. The method of reduction consists in addin 
4 constant quantity to the observations at each station; an 
the same constant is adhered to throughout the entire year. 
That this mode of reduction is erroneous appears from a com- 
Parison of the observations on Mt. Washington with the obser- 
vations at neighboring stations near the level of the sea. In 
the following table, column 2d shows the mean height of the 
barometer on Mt. ashington (reduced to sea-level by the 
Signal Service method) for each month of the year according to 
the observations of six years (1871-7). Column 3d shows the 
mean of the observations at Burlington, Vt., and Portland, Me. 
(also reduced to sea-level) for the same period; and column 4th 
Am, Jour. Sct.—Turrp a Vou. XIX.—No. 110, Fes., 1880. 
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