# Monographs of the United States Geological Survey, Band 22

U.S. Government Printing Office, 1893

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Seite 86 - ... one division for each revolution. This form is the most trustworthy that has yet been devised, but is not altogether satisfactory, and many topographers prefer to count the revolutions of the wheel directly, using an arrangement by which a bell is rung at each revolution. An experience covering many thousands of miles of measurement has shown that as a working method of measuring distances on roads the wheel is superior to the stadia, alike as to accuracy and rapidity. A traverse man is generally...
Seite 32 - COMPARISON OF TIME. After time has been thus observed the chronometers at the two stations should be compared by telegraph. Chronometers are compared in the following manner: The chronometer at one station .being in circuit with the chronograph and recording upon it, the chronometer at the other station is switched into the general telegraphic circuit, by which it is brought to the first station and switched into the local circuit there, so that the two chronometers register upon the same chronograph,...
Seite 73 - ... greater distances than 10 miles, if it can be avoided. An error of 1' in the measurement of the angle is at this distance about 15 feet, while the uncertainty of refraction in such a length of line is necessarily great. TRAVERSE WORK. As stated...
Seite 98 - Take likewise the value of h', and find the difference. If the barometrical heights have not been previously reduced to the same temperature, or to the freezing point, apply to the difference the correction found in Table II opposite the number representing T — T'; we thus obtain the approximate difference of level, D.
Seite 41 - ... is reduced to a small fraction of the number necessary in the use of bars, while the uncertainty in regard to the temperature of the measuring apparatus is reduced to a minimum by carrying on the measurement at night or in cloudy weather. The expense of the measurement is greatly reduced since fewer men are required, the work of preparing the ground and the work of measuring are much lessened, and the rapidity of measuring is increased manyfold.
Seite 70 - ... observations. These, with the observed angles and the computed distances between the stations, form the data from which the latitudes and longitudes of the stations and the azimuths of the lines connecting them are computed. The difference in latitude between two adjoining stations is obtained from the following equation, based upon the Clarke spheroid: Township corner....
Seite 86 - The alidade consists of a brass ruler, 12 inches long, with folding sights. The edge of the ruler is graduated to facilitate platting of distances. Ordinary drawing paper backed with cloth is used for plane-table sheets, and is attached to the board by thumb tacks. When traversing is done along roads, as is commonly the case, distances are measured by counting the revolutions of a wheel, usually one of the front wheels of a buggy or buckboard. For counting the revolutions, various automatic devices...
Seite 55 - The effect of an error of collimation on the circle reading for any direction varies as the secant of the altitude of the object observed. The effect on an angle between two objects varies as the difference between the secants of their altitudes. This effect is eliminated either by reversing the telescope in its...
Seite 17 - The telescope has a focal distance of 27 inches and a clear aperture of 2.5 inches. Its magnifying power with diagonal eyepiece is 74 diameters. The length of the axis of the telescope is 16 inches. For use as a zenith telescope, the instrument is equipped with a vertical circle reading by vernier to 20 seconds, attached to which is a delicate level. In the focus of the...
Seite 20 - Before beginning to observe, the instrument should be closely collimated and drawn into the meridian. Upon the approach of the first star of the pair to the meridian, the instrument should be set for it, using the vertical circle for that purpose, and setting the spirit level upon the vertical circle as nearly level as possible. Then, as the star traverses the field of the telescope, keep the movable thread in the reticule upon it by means of the micrometer screw until it crosses the middle verticle...