The elements of physiological physics The elements of physiological physics: an outline of the elementary facts, principles, and methods of physics; and their applications in physiology elementsofphysio00mgre Year: 1884 278 PHYSIOLOGICAL PHYSICS. [Chap. xxm. means of the float and thread move the wheel, which has attached to it a hand travelling over a dial, and indicating the variations. In the aneroid barometers mercury columns are discarded, and a metallic box, partly exhausted of air, is employed. Variations of pressure cause movements of the top of the box, which are transmitted to lever
The elements of physiological physics The elements of physiological physics: an outline of the elementary facts, principles, and methods of physics; and their applications in physiology elementsofphysio00mgre Year: 1884 278 PHYSIOLOGICAL PHYSICS. [Chap. xxm. means of the float and thread move the wheel, which has attached to it a hand travelling over a dial, and indicating the variations. In the aneroid barometers mercury columns are discarded, and a metallic box, partly exhausted of air, is employed. Variations of pressure cause movements of the top of the box, which are transmitted to levers, and move an indicator. The position of the indicator is determined for different pressures by means of the mercury column, and these positions are then marked on a dial over which the indicator moves. Effects of atmospheric pressure.—It has been seen that into a tube from which the air is ex- hausted, and in which the atmospheric pressure, there- fore, is reduced to zero, a column of mercury will rise to 30 inches, and a column of water to 34 feet. Other fluids will also rise to a height in the inverse ratio of their density. It is obvious that there is thus afforded a means of raising water or other liquid from a low level to a higher one. It is equally obvious that there is a limit to the height to which the liquid can be raised by exhaustion of the air ; that, in fact, it will rise only to the height sufficient to produce a downward pressure equal to the upward pressure of the atmosphere, a height which, as already said, varies with the density of the liquid. The suction pump is an application of these facts. It consists essentially of a barrel or cylinder fitted with a piston (Fig. 120). The lower part of the barrel is Fi<* 120.— continued into a tube which dips into the fraction water to be pumped. When the piston is pulled from the lower end of the barrel to the upper, the space it leaves below is devoid of air, and the water rises in the tube, filling the barre
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