Leveling: barometric, trigonometric and spirit (Google eBook)

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D. Van Nostrand, 1887 - Leveling - 145 pages
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Page 11 - B by means of four large screws P and the ring R ; on the ring R screws the cap S, which covers the lower parts of the cistern, and supports at the end of the adjusting screw O.
Page 11 - ... up of a glass cylinder F, which allows the surface of the mercury q to be seen, and a top plate G, through the neck of which the barometer tube / passes, and to which it is fastened by a piece of kid leather, making a strong but flexible joint.
Page 19 - The instrument can then be hung up and readjusted. The tube and its contents having been undisturbed, the instrument should read the same as before. If a little mercury has been lost during the operation, and there is none at hand to replace it, no serious harm has been done; but if much is lost, the open end of the tube may become exposed in inverting the instrument, in which case air may enter.
Page 17 - If the cistern should become dirty it can be cleaned with safety, and without changing, in the slightest degree, the zero of the instrument. Everything used in the operation must be clean and dry. Avoid blowing upon any of the parts, as the moisture from the breath is injurious. The instrument being placed upright, the cistern uppermost, unscrew and take ofi the brass casing which incloses the wooden and leather part of the cistern. This wooden part (which has th...
Page 37 - The laws of the distribution and transmission of moisture through the atmosphere are too little known, and its amount, especially in mountain regions, is too variable, and depends too much upon local winds and local condensation, to allow a reasonable hope of obtaining the mean humidity of the layer of air between the two stations by means of hygrometrical observations taken at each of them.
Page 80 - ... correspond to inches of the ordinary barometer column, the inches being divided into tenths, and the tenths usually into four parts. At the back of the instrument is a little screw which presses against one end of the exhausted box...
Page 9 - F, which allows the surface of the mercury to be seen, and a top plate G, through the neck of which the barometer- tube t passes, and to which it is fastened by a piece of kid leather, making a strong but flexible joint. To this plate, also, is attached a small ivory point h, the extremity of which marks the commencement or zero of the scale above. The lower part, containing the mercury, in which the end of the barometer tube t...
Page 83 - ... place it in position for observing, as does the mercurial barometer, and being at all times in condition for immediate and direct reading, as is a watch. It is inferior, however, as a hypsometric instrument to the mercurial barometer, chiefly because it is subject to the following sources of error: 1. The elasticity of the corrugated top of the vacuum chamber is affected by rapid changes in pressure. 2. Its readings are affected by changes in temperature which it is impossible to readily compensate....
Page 91 - When water is heated, the elastic force of the vapor produced from ii. gradually increases until it becomes equal to the incumbent weight of the atmosphere. Then, the pressure of the atmosphere being overcome, the steam escapes rapidly in large bubbles, and the water boils.
Page 13 - Then reverse the tube over a basin, when, by slightly relieving the pressure against the end, the weight of the column of mercury will force some out, forming a vacuum above, which ought not to exceed one-half an inch. Closing up again tightly, let this vacuum bubble traverse the length of the tube on the several sides, when it will absorb those minute portions of air, now greatly expanded from removed atmospheric pressure, that were not drawn at the first gathering. The perfect freedom from air...

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