# Circular, Volume 3, Part 4

U.S. Government Printing Office, 1909 - Meteorology

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Page 16 - ... correction for capacity.'' (See par. 24.) Tffl Kn. i KI, 'i. — Tueli barometer cistern I 19. Contracted barometer scale. — As the correction for capacity in barometers with fixed cisterns remains the same so long as the quantity of mercury within the barometer and the inside area of tube and cistern are unchanged, it will not be necessary to apply a capacity correction to every reading made, provided we use on the barometer a scale having all its divisions shortened by just the proper amount...
Page 14 - Now, since we imagine these scales to represent inches and tenths, then figure 5 will read, 30.15 inches. 13. Estimation of fractions on a vernier. — In many cases it will happen that no single line on the vernier will be exactly coincident with a scale line, but that one line will be a little above while the next line on the vernier will be a little below the corresponding scale lines. In the case shown in figure...
Page 14 - In figs. 7 and 8 are shown verniers applied to a barometer scale having 20 parts to the inch. In this case 24 parts on the scale are divided into 25 parts on the vernier. By the principle already explained in paragraph 12, the value of the subdivisions effected by such a vernier, or, as it is most frequently expressed, the least count of the vernier, will be ^ of jV = TVT of an inch.
Page 14 - ... 4, the first line above the zero on the vernier is one-tenth part of the space, the next line two-tenths, the next three-tenths, etc., distant from the line next above on the scale. When, therefore, we find the vernier in such a position as shown in figure...
Page 13 - ... the other, and from this circumstance the position of the zero line of the vernier in reference to the scale can be very accurately determined, as will be readily understood from a study of the following figures and explanation...
Page 78 - ... barometer, cistern uppermost, into the leather case. 147. On steamboats or railroads the barometer, if hung up in any manner, should be secured against striking or pounding the side of the room or car. In wheeled vehicles the barometer should be carried by hand, supported by a strap over the shoulder, or held upright between the legs. It should not be allowed to rest on the floor, as a severe jolt may break the tube. On stage routes, when impracticable to carry it by hand, hang the barometer...
Page 78 - The wood shoulabe neatly cut away, if necessary, but only sufficiently to receive these projecting parts. Insert the barometer, cistern uppermost, into the leather case. 147. On steamboats or railroads the barometer, if hung up in any manner, should be secured against striking or pounding the side of the room or car. In wheeled vehicles the barometer should be carried by hand, supported by a strap over the shoulder, or held upright between the legs. It should not be allowed to rest on the floor,...
Page 10 - barometers^ Weather Bureau pattern. — In order that the height of the mercurial column may represent accurately the true pressure of the air, and in order to detect the comparatively small changes of pressure from day to day, many refinements are necessary in the construction of the instrument and great precision of measurement is required. An excellent form of the mercurial barometer, satisfying the requirements just stated, was devised by Fortin, and is now very widely used the world over. The...
Page 10 - ... top and inclosed in a thin metal tube, through which large openings are cut on opposite sides, exposing to view the glass tube and mercurial column. The graduated scale is formed at one side of this opening, and a short tube or sleeve, also graduated (shown at C, figs.
Page 10 - ... pounds, which, multiplied by 30, gives the ordinary sea-level pressure of the air to be 14.718 pounds per square inch. This quantity is frequently used by engineers and is called a pressure of one atmosphere. In the main, it is nothing more than the weight of an air column having a sectional area of one square inch and extending vertically to the upper limits of the atmosphere. For meteorological purposes the force exerted by this weight is to be expressed in terms of millibars, a millibar being...