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Geodetic Science 3 3 , — Home Questions Tags Users Unanswered. Recommendation for a book for geographical distance calculations [closed] Ask Question. Sayantan Roy Sayantan Roy 14 5 5 bronze badges. This starts at the begining with: I.
Well thanks a lot. I would like basic concepts to write about in terms of literature review. Sills some 3 feet underground were used for the tower, but not for the tripod.
The station mark was placed after the signal was up. The work was let by the vertical foot. The con- tractor, with 15 men and 2 teams, would frame, erect, and com- plete a signal in 2 days. Recently the Lake Survey has adopted an elevated signal and observing-stand, made of gas pipe, which has proved very satisfac- tory, and more economical than timber, on account of its portability.
The method of erection is shown in Fig. The upper portion of the instrument pyramid is put together on the ground and then erected.
The upper part of the observing stand is then put to- gether around the pyramid. Tackles are attached at the four corners as shown, and this upper portion of the stand is drawn up so that the next section can be attached underneath. Afterwards either structure can be drawn up, if the other is high enough for attaching the blocks, and an additional section attached, the workmen remaining on or near the ground. Guys are used for steadying during erection. A portable tripod and scaffold, having a floor about 12 feet high, is shown in Fig.
The tripod legs are 6 by 8 inches, 18 FIG. They are held by an inch bolt 16 inches long, and by three horizontal braces. The scaffold posts are 5 by 5 inches, 16J feet long; the horizontal braces are 7 feet long, and the diagonal ones 10 feet. The posts are interchangeable, and the braces are FIG. The posts all extend about 2 feet into the ground, and the floor is placed from 2 to 3 feet below the top. Only a few hours are required for erection after everything is in readiness. One of the most common forms in use is called the gas pipe heliotrope, Fig. A piece of 2-inch iron pipe FIG. The whole instrument is supported by a wood-screw, which can be screwed into a tripod head or other block.
It is set up directly over the station mark, or on line and a few feet in front of it, and the cross- hairs of the telescope brought on the distant observing party. This ring is maintained by gently tapping the mirror at intervals of from J to 2 minutes. The adjustment of the instrument should be tested by bring- ing the cross-hairs on an object within a few hundred feet, throw- ing the light as above, and noting if it falls as far above the object as the rings are above the cross-hairs.
The synthetic juxtaposition allowed one to highlight the evolution, considered by the author an important feature of the non-invasive way of introducing changes. Fedele R. References 1. Scott Fitzgerald , Paperback Students may also hand in their work from the field, including field notes atmospheric conditions, metadata and sketch of survey setup.
A more recent form, used on the Coast Survey, is shown in Fig. The mirror is rotated by tangent screws and the telescope can be more accurately pointed.
The Steinheil heliotrope differs from that already described in having only one mirror and no rings, making it very simple and convenient for reconnoissance work. The axis of the frame is hollow, and it contains a small lens, L, Fig. By turning this axis towards the sun a hole through the silver- ing of the mirror allows a beam of sunlight to reach the lens and be concentrated upon the white surface. It is reflected from the Eq.
Enough of these rays will be reflected from the back to give an image of the bright spot, C, and in a direction, AO, directly opposite to the reflection of sunlight from the face of the mirror.
Hence, if the eye be placed at so as to see the observ- ing party through the opening A in the direction AT, and the mirror be turned until the bright spot C is seen the axis pointing towards the sun , the sunlight will be reflected in the direction OAT to the observing party. The distance from the reflecting surface to the lens is adjust- able for focus.
When the alignment has been once secured, if there is no natural landmark in range, a pole should be set up at a distance of to feet, so that its sharp top will be on or a little below the line. The light can then be shown, and will often be seen by the observing party, on days when haze and smoke will prevent the heliotroper from seeing even the outline of the hill or mountain at the observing station.
A second mirror is usually supplied, which can be screwed up and light reflected from it to the first, if at any time the first falls in shadow or its angle of incidence becomes so great that the re- flected beam will not fill the diaphragm. Extreme accuracy in pointing is not essential, the range being about the diameter of the sun, or 32 minutes. About a 2-inch mirror is used for lines from about 20 to 60 miles, and usually in connection with pole or other signals.
For shorter lines a pasteboard or other screen with a smaller opening should be attached to the second ring. For longer lines larger mirrors are used. Thus, on the U.
Lake Survey, for the longest lines a common mirror, 9 by 12 inches, was set up, and light thrown through a circular hole in a wooden screen some 20 feet distant in the direction of the observing station, this having a diameter of from 8 to 10 inches on sides of 90 to miles. On the longest line ever observed, Mt. Lola in northern California, miles, a helio 12 inches square was used. Too much light gives, by irradiation, a diameter too large for accurate bisection, and increases the unsteadiness.
An opening suited to the distance, or one which will subtend from one-fourth to one-fifth of a second, will give in quiet air a small, bright disk easy to bisect. An intelligent and very faithful person should be picked out for the heliotroper; otherwise delay and vexation will result. If he is to occupy the station a long time, he can usually be picked up with economy in the locality; if for only a short time, it may be more economical to have one who is familiar enough with the work and with instruments to go to new stations and establish himself without assistance, when directed by the observing party.
Night Signals. Lamps with inch reflectors for short lines and the Drummond light for long ones were used on the English Ordnance Survey in the last century, while night signals have been extensively used in the recent prolongations of the Nouvelle meridienne de France by M. Perrier, and Argand lamps and heliotropes are exclusively used in India. The electric light, in the focus of a reflector 20 inches in di- ameter and 24 inches focal length, proved very successful recently on a line of miles across the Mediterranean, where, on account of fog and mist, a inch heliotrope had failed to once show dur- ing a three months' trial.
On the Coast Survey experiments were made in' with night signals Report, , App. The optical collimators used were M.
Perrier's French lamps, Fig. The large lens has a focal length of 24 inches, and a di- ameter of 8 inches. The emergent rays subtend an angle of about 1. The intensity of light, as compared with the magnesium, was about as 2 to 5.