Science for beginners . rectedreading is therefore in. 155. Correcting the Barometer for Altitude.—Since thebarometer shows the weight or pressure of the atmosphere, itis evident that it will read highest when at the bottom of theatmosphere. The higher up into the atmosphere we carry abarometer, the less air there is above to press upon themercury, and the lower the barometer will read. This factwas discovered soon after Galileo found that air had , a Frenchman, heard of Torricellis experiment in several years of experimenting, Pascal concluded thatthe mercury in
Science for beginners . rectedreading is therefore in. 155. Correcting the Barometer for Altitude.—Since thebarometer shows the weight or pressure of the atmosphere, itis evident that it will read highest when at the bottom of theatmosphere. The higher up into the atmosphere we carry abarometer, the less air there is above to press upon themercury, and the lower the barometer will read. This factwas discovered soon after Galileo found that air had , a Frenchman, heard of Torricellis experiment in several years of experimenting, Pascal concluded thatthe mercury in the tube would stand lower on a mountaintop than at its base. He carried a tube to the top of a hightower and noticed a slight drop in the mercury column. Hethen asked his brother-in-law, who lived near the Puy de THE USE OF WEATHER INSTRUMENTS 143 Dome, a mountain in southern France, to carry a barometerto the summit of the mountain. This Perier did on Septem-ber 19, 1648, and Pascals theory was confirmed (Fig. 105).. o-SEA LEVEL—o- Fig. 105.—Atmospheric pressure varies with altitude. A showselevation of New Orleans, (8 ft.); B, of Oklahoma, 1150 ft.; C, ofDenver, 5600 ft. Barometer readings must be corrected for altitudebefore they can be compared. The barometer is used in studying the weather. Barometerreadings at sea level are ordinarily about 30 in.; at the alti-tude of Chicago, about in.; at Denver, about 23 in.; andat the top of Pikes Peak, about 15 in. Scarcely any twoweather stations have the same elevation. Therefore, in orderto compare barometer readings with those of other weather ob-servers, all readings must be corrected for altitude as well asfor temperature. In doing this it is customary to change allreadings to what they would have been if the barometerhad been at sea level. These corrections are easily obtainedfrom Table YI. (See p. 146). Directions for Using Table VI.—The proper correction is foundfrom Table VI in a manner similar to that followe
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