A treatise on the aneroid, a newly invented portable barometer. With a short historical notice on barometers in general, their construction and use / [Edward John Dent].

  • Edward John Dent
Date:
1849
Catalogue details

Licence: Public Domain Mark

Credit: A treatise on the aneroid, a newly invented portable barometer. With a short historical notice on barometers in general, their construction and use / [Edward John Dent]. Source: Wellcome Collection.

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    No. 1, is made with a capillary tube, about twenty-seven inches long, and represented at No. 2, as removed from its case. The lower part of this tube scarcely exceeds the thirtieth part of an inch in diameter, but it terminates at the top A in a larger bore, four or five inches long, and nearly three-tenths of an inch in diameter. From the ivory plate D, parallel with this tube, the navigator reads off the scale, perhaps not knowing that only a small capillary tube extends the whole length downwards to the cistern C, since this tube of diminished bore is concealed from his view by the outer case. This capillary tube, which was intended to counteract the disturbing effect of the ship’s motion, is attended with a serious evil; it renders the rise and fall of the mercury in the upper part of the instrument so sluggish, that it does not show any increase or decrease of the column, under an interval of five minutes or more. For example, if you incline the barometer to a nearly horizontal position, until the mercury has risen in the upper part, and then restore it to its vertical position, you will perceive that an interval of several minutes will occur before its original indication is shown. Such are the defects of an instrument which the navigator so frequently consults for his guidance, while he is often, perhaps, unconscious of its labouring under the imperfections to which the foregoing remarks have shown that it is essentially liable. Surely, then, it is a desideratum of the utmost consequence that the barometer for shipboard should be improved. The next instrument to be described is that which is known at the present time by the name of a Sym- piesometer. This was also the invention of the great Dr. Hooke, and preceded his ingenious Wheel Barometer. It consists of two parts. The one (A B) No. 1, is a common spirit thermometer ; the other, No. 2, (C D), a tube filled with air from C to E, and from thence, to the
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