SIMPLE BAROMETERS.

Auckland Star, Volume XXIII, Issue 102, 30 April 1892, Page 3 (Supplement)

SIMPLE BAROMETERS.

Air and Water Barometers More or liesS Useful ami of Scientific Interest. A barometer is an instrument designed to measure the weight or pressure of tho atmosphere as it varies from time to time. Popular Science News explains, however, that for many purposes it .s not necessary to measure the actual pressure of air, but only the variations of pressing, and for tills there are several simple devices. It it; evident that if a quantity of air is sealed up in a vessel, the pressure of the inner and outer air ou the sides of the vessel will be equal as long as the pressure of tho

A CUT.IOtTS OLD BAROMETER. outer atmosphere remains unchanged. But if the atmospheric pressure increases, there will be an inward pressure upon the outer sides of the vessel. If, on the contrary, tho atmospheric pressure diminishes, tho pressure on the vessel is from within ontr ward. A simple way of making these changes of pressure visible isshewuiu acurious old. barometer which, with ethers noted hereafter, was originally illustrated in La Nature. It consists of an ornamental glass flask with a single opening in the side, to. which is attached a glass tube bent ujv. ward at a right angle. The flask is filled! with water to a poinb above the opening, t , us making it air tight, and the varying pressure, between the outer <md inner air is indicated by the rise and fall of tho level of the water in the tube. Popular Science Xcws also describes tha apparatus shown at the left hand of the second illustration. It is made from an ordinary bottle, provided with a well fitting stopper, preferably of rubber, though, cork will answer if previously soaked ra. melted parafiine. The stopper is perforated, and a glass tube, about a yard in length and open at both ends, is passed through it to the bottom of the botfcls. Before putting the apparatus together the bottle is filled about one-quarter full of water and the tube almost entirely full. If the upper end of the tube is kept closed by the finger the water will not run out, even when it is inverted, and when arranged as shown in the illustration, tha column of water should stand a tew inches below the top of the tube, and will rise and fall according as the pressure of the atmosphere diminishes or increases. That is, when the ordinary mercurial barometer rises this water barometer will fall, and vice versa. An objection to these barometers is thai they are more sensitive to changes of tern-, perature than of pressure, and on a warm day the column of water will rise in tha tube, notwithstanding increased atmospheric pressure. At A and B is represented an improved form of air barometer. It consists of a* glass tube, on one end of which is blown a glass bulb, the other end being left open,

but slightly narrowed by heating in a flame. A small quantity of mercury is ror troduced into the tube to serve as an in-: dcx. When the barometer is in the posi-v tion A, the pressure on the air in the bulb equals the outside atmospheric pressure, plus the weight of the mercury; when ib is reversed, as in 13, it equals the outside pressure, minus the weight of the raercury. By suspending the instrument successively in the two positions tind reading the different heights of the mercury on the scale, the atmospheric pressure may be calculated by a set of tables which acccoa- 1 pany the instrument.