. The climate and weather of Baltimore . .19 .18 .21 .12 .11 .08 .08 .08 .13 .10 .16 .17 Average for the year inches. Average amplitude inches. Table V shows the average sea-level barometric pressure for each day of theyear. The period of observation covers the 30 years from 1871-1900. Thedaily mean is based on three readings of the mercurial barometer at about 7 a. m., 3 p. m. and 11 p. m., from 1871 to June 1888, and on two readings at 8 a. m. and 8 p. m., from July 1888 to 1900. The correction for diurnal var-iation has not been applied, but th
. The climate and weather of Baltimore . .19 .18 .21 .12 .11 .08 .08 .08 .13 .10 .16 .17 Average for the year inches. Average amplitude inches. Table V shows the average sea-level barometric pressure for each day of theyear. The period of observation covers the 30 years from 1871-1900. Thedaily mean is based on three readings of the mercurial barometer at about 7 a. m., 3 p. m. and 11 p. m., from 1871 to June 1888, and on two readings at 8 a. m. and 8 p. m., from July 1888 to 1900. The correction for diurnal var-iation has not been applied, but this is extremely small for the observationsmade at 7 a. m., 3 p. m., and 11 p. m., and about -f .01 inch for the series ofreadings at 8 a. m. and 8 p. m. The number should be added to eachof the figures in the body of the table. The monthly range of the mean dailypressure is indicated in the last line of the table. The figures of this tableare also represented graphically in curve D of Plate 3. 46 THE CLIMATE OF BALTIMORE 1871 1875. Fig. 7.— Variations in the Mean Montlily Pressure (Expressed as Departures fromthe Normal Values for the Month, ia Thousandths of an Inch of Mercury). SeeTable VII. MARYLAND WEATHER SERVICE 47 during the summer months when it is generally less than inch,and greatest in the winter months, when it rises to inch, and, occa-sionally, to inch. To what extent these irregular interdiurnalvariations would be eliminated in a longer series of observations is amatter of conjecture. To a marked extent at least they are probablypersistent and due to a periodic recurrence of certain types of weatherat certain seasons of the year. Of special interest is the comparatively rapid rise in pressure fromAugust to September, and the arrested upward movement in October,more clearly shown in Fig. 6, constructed from monthly averages, thanin the serrated curve of daily means. The barometric waves of short period vary greatly in length and arenot genera
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