This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1852 Excerpt: ...vacuum barometer may be relied on for all ordinary purposes; and the following table will supply the means of ascertaining the comparative gradients of a railway by one of them. Being an extract, by permission, from the elaborate table of W. Galbraith, M.A., dedicated to Sir Thomas M. Brisbane, Bart. In this table, the ...
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1852 Excerpt: ...vacuum barometer may be relied on for all ordinary purposes; and the following table will supply the means of ascertaining the comparative gradients of a railway by one of them. Being an extract, by permission, from the elaborate table of W. Galbraith, M.A., dedicated to Sir Thomas M. Brisbane, Bart. In this table, the middle column exhibits heights in English feet, corresponding to the height of the barometer, shown in the first column, in inches, tenths, and hundredths; the proportional parts to thousandths are given in the right-hand column. Example.--It is required to find, in English feet, the difference of level between Dover and Folkstone Railway-stations AND THEIR APPLICATION. 155 by the barometer, Dover indicating 309125 inches, and Folkstone 30-000. In the table at 30-12 we find 29332 0, and in the column A at 5 we have 43; which, added to 29332-0, gives for Dover 29336-3. On referring to the 30-000 inches in the table, by which Folkstone is indicated, we find 29227-8. The one, subtracted from the other, gives the difference in feet between the two stations: --Dover.... 29336-3 Folkstone... 29227-8 Feet. 108-5 Folkestone-station, therefore, is higher than that at Dover by 108-5 feet. The above experiment was actually made while sitting in a railway-carriage, and the example will serve as a guide for taking any measurement by the barometer. The natural philosopher is enabled, by means of the Aneroid, to discover the quantity necessary for thermometrical correction. He has only to expose the instrument to the temperature of the external air, (having set the hands in coincidence, ) and afterwards place it before the fire, until the thermometer is at 100. Any variation of the hand, divided by the degrees of the thermometer, will give the quantity for ea.
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