Defects and Disadvantages of the Present Form of Tripods for Field-instruments: With a Description of a New Tripod for Instantaneously Setting and Leveling Up Field Instruments

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Heller & Brightley, 1878 - Surveying - 86 pages
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Lots of fascinating information on the making and use of surveying instruments. Really good for me, anyway, as an amateur surveyor and mapmaker.

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Page 23 - PHILADELPHIA, November 7, 1876. REPORT ON AWARDS. Product.— SURVEYING AND ENGINEERING INSTRUMENTS. Name and Address of Exhibitor— HELLER & BRIGHTLY, Philadelphia. The undersigned (judges on instruments of precision), having examined the products herein described, respectfully recommend the same to the United States Centennial Commission for Award . This firm has lately become distinguished by improvements on the customary methods of constructing Surveying Instruments * * * improved details —...
Page 11 - ... the east. The times at which the needle reaches its eastern and western elongations vary with the seasons of the year (with the sun's declination), happening a little earlier in summer than in winter. The angular range between the eastern and western elongations varies also with the season of the year. The average position of the needle for the day is called the mean magnetic meridian. At about six o'clock in the evening (and for about an hour before and after), throughout the year, the position...
Page 24 - ... the Leveling Instrument of this last expert, which he declared was in perfect order and adjustment, was found, on trial by us, to be out of adjustment -^ of a foot in 300 feet, perhaps his opinion may not carry much weight. The result of four series of test levels in France, of from 45 to 140 miles, averaged a difference of...
Page 10 - If this star were precisely at the point in which the axis of the earth, prolonged, pierces the heavens, then the intersection of the vertical plane passing through it and the place, with the surface of the earth, would be the true meridian. But the star being at a distance from the pole equal to 1...
Page 11 - For reducing the direction of the needle observed at other hours to the mean magnetic meridian the following table is furnished. It gives to the nearest minute the variations of the needle from its average position during the day, for each hour in the day for the four seasons of the year. Table for reducing the observed declination to the mean declination of the day.
Page 10 - To the eye of an observer, this star is continually in motion, and is due north but twice in 23 h. 56 min. ; and is then said to be on the meridian. Now, when it departs from the meridian, it apparently moves east or west, for 5 h.
Page 10 - Tables show the times of its eastern and western elongations. The eastern elongations are put down from the beginning of April to the end of September, and the western from the beginning of October to the end of March. The western elongations in the first case, and the eastern in the second, occurring in the daytime, cannot be used. Some of the others put down in the table are also Invisible, occurring in the evening before it. is dark, or after daylight in the morning. In such case (if it be necessary...
Page 11 - ... the east which soon ceases. The needle is then said to be at its eastern elongation; its north end then begins a retrograde motion towards the west, and at about one o'clock in the afternoon reaches the point at which it is said to be at its western elongation, after which it again turns back...
Page 11 - The needle is then said to be at its eastern elongation; its north end then begins a retrograde motion towards the west, and at about one o'clock in the afternoon reaches the point at which it is said to be at its western elongation, after which it again turns back towards the east. The times at which the needle reaches its eastern and western elongations vary with the seasons of the year (with . the sun's declination), happening a little earlier in summer than in winter. The angular range between...
Page 24 - Transits) was expressed by the assistants; their objections were these, — first, an eccentricity or imperfection of graduation of two minutes, more rarely three minutes, was frequently found in the reading of the verniers of the horizontal limbs, etc. — Extract from Report of Chief of Engineers, CJ.

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