. A directory for the North Atlantic Ocean, comprising instructions general and particular for its navigation. Pilot guides. 682 EEMAEKS ON THE BAROMETEB. hermetically sealed, metallic box, from which almost all the air Las been withdrawn, and which is kept from collapsing by a spring. The top of the box is corrugated. When the atmospheric pressure rises above the amotint which was recorded when the instrument was made, the top is forced inwards; and vice versa, when the pressure falls below that amount, the top is pushed outwards by the spring. These motions are transferred by a system of lev
. A directory for the North Atlantic Ocean, comprising instructions general and particular for its navigation. Pilot guides. 682 EEMAEKS ON THE BAROMETEB. hermetically sealed, metallic box, from which almost all the air Las been withdrawn, and which is kept from collapsing by a spring. The top of the box is corrugated. When the atmospheric pressure rises above the amotint which was recorded when the instrument was made, the top is forced inwards; and vice versa, when the pressure falls below that amount, the top is pushed outwards by the spring. These motions are transferred by a system of levers and springs to a pointer, which moves on a dial like that of a wheel-barometer. It is at once evident that the instrument must be graduated experimen- tally, as it cannot measure pressure absolutely, but afifords indications relatively to a mercurial Barometer, its sensibility depending, inter alia, on the quality of the metal of which the box is made. Aneroids are very sensitive, but unfortunately they do not preserve their accuracy. If a table of corrections be determined for an Aneroid, it will be found that after a time the latter has undergone some change, and that the values of the corrections will require alteration, so that re- comparison with a Standard Barometer will be necessary (see page 108). In every case of such comparison the readings of the mercurial Barometer should be reduced to 32°. A most serious objection to the scientific utility of these instruments is their liability to injury, owing to rust, or to the alteration of force in the springs used in their construction. However, for the reasons above stated, the Aneroid is especially suitable for fishermen and pilots, or seafaring persons employed in boats or small coasting vessels, in which there is not space to suspend a Barometer. For further information, on the practical use of the Barometer, reference should be made to the Section on "The Motions and Pressure of the Atmosphere," pages 108
Size: 2462px × 1015px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauth, bookcentury1900, bookdecade1910, booksubjectpilotguides
