. Barometers and the measurement of atmospheric pressure. A pamphlet of information respecting the theory and construction of barometers in general. Barometers; Meteorological instruments. 22 a small wheel or drum on the axis ff, upon which is mounted the hand as seen. At h is shown a small spiral steel spring, like the hair- spring of a watch, which serves to take up the slack in the loose con- nections of the numerous joints, levers, and links. At r is shown, also, a small counterpoise weight attached to the bell-crank lever to aid in securing a more stable position of the index when the bar
. Barometers and the measurement of atmospheric pressure. A pamphlet of information respecting the theory and construction of barometers in general. Barometers; Meteorological instruments. 22 a small wheel or drum on the axis ff, upon which is mounted the hand as seen. At h is shown a small spiral steel spring, like the hair- spring of a watch, which serves to take up the slack in the loose con- nections of the numerous joints, levers, and links. At r is shown, also, a small counterpoise weight attached to the bell-crank lever to aid in securing a more stable position of the index when the barometer is placed in different positions; that is, whether the dial is horizontal, or vertical, or turned to one side or the other. The point of attachment of the link m to the bell-crank lever is sometimes adjustable so that the movements of the hand can be made to correspond to the value of the scale graduations. The steel spring R is also slightly adjustable by means of a screw from the underside threaded into the part N. This permits adjusting the hand to any particular point of the scale to give correct read- ings. 48. Effects of temyeror- ture.—The steel spring and the feebler elastic re- action of the composition metal of the vacuum chamber are appreciably weakened by increase of temperature, so that in some cases a rise of the pressure may seem to oc- 3ur which is really caused by the weakening of-the spring. In some cases ef- forts are made to com- pensate for this by leav- ing a small quantity of air in the vacuum cham- ber, which when heated increases its pressure upward and tends to offset the weakening effect upon the springs. A better plan is to make the lever I of two differ- ent metals, viz, brass and iron, firmly brazed together. The differ- ential expansion of these two metals with temperature changes pro- duces flexure in the lever. By filing and adjusting the bimetallic bar, the flexure due to temperature can be made very nearly to balance the effect of tem
Size: 1318px × 1897px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookpublisherwashingtonu, booksubjectbarometers
