. The principles of physics. Try to pull the piston out again. Why do younot succeed? Hold the apparatus invarious positions, so that Jhe atmospheremay press down, laterally, and up,against the piston. Do you discoverany difference in the pressure which itreceives from different directions 1 . HOW ATMOSPHERIC PEESSURE IS MEASURED. 157 130. How atmospheric pressure is measured. Experiment 5 (preliminary).-Take a U-shaped glass tube (Fig. 125)half fill it with water, close one ^ = i^ end with a thumb, and tilt thetube so that the water will runinto the closed arm and fill it;then restore it to i
. The principles of physics. Try to pull the piston out again. Why do younot succeed? Hold the apparatus invarious positions, so that Jhe atmospheremay press down, laterally, and up,against the piston. Do you discoverany difference in the pressure which itreceives from different directions 1 . HOW ATMOSPHERIC PEESSURE IS MEASURED. 157 130. How atmospheric pressure is measured. Experiment 5 (preliminary).-Take a U-shaped glass tube (Fig. 125)half fill it with water, close one ^ = i^ end with a thumb, and tilt thetube so that the water will runinto the closed arm and fill it;then restore it to its original ver-tical position. Why does not thewater settle to the same level inboth arms ?. Fig. 125. Mg. 126 represents a U-shaped glass tube closed at oneend, 34 inches in hight, and with a bore of1 square inch section. The closed arm hav-ing been filled with mercury, the tube isplaced with its open end upward, as in thecut. The mercury in the closed arm sinksabout 2 inches to A, and rises 2 inches inthe open arm to C ; but the surface A is 30inches higher than the surface C. This canbe accounted for only by the atmosphericpressure. The column of mercury B A, con-taining 30 cubic inches, is an exact coun-terpoise for a column of air of the samediameter extending from C to the upperlimit of the atmospheric ocean, — an un-known hight. The weight of the 30 cubic inches of mer-cury in the column B A is about the weight of a column of air of 1 square-inch section,extending from the surface of the sea to the upper limit ofthe atmosphere, is about pounds. But in fluids gravitycauses equal pressure in all directions. Hence, at the levelof the sea, all bodi
Size: 2366px × 1056px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectphysics, bookyear1895
