Elements of surveying by Davies Charles 1798-1876

Author:Davies, Charles, 1798-1876. [from old catalog]
Language: eng
Format: epub
Tags: Surveying, Navigation
Publisher: New York, A. S. Barnes & company
Published: 1866-03-25T05:00:00+00:00

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ELEMENTS OF SURVEYING. [BOOK 11

a oeciion. The sections of a township are numbered fix)in 1 to 86, beginning at the north-east angle, and each con* tains 640 acres

The diagram exhibits the 86 sections of a township^

To describe a section accurately, we say, section number 5, in township number 4 north, in range 8d west of a known meridian; the one, for example, drawn6through the mouth of White river. The description fixes precisely the place of the section. Go to the 8d range of \ownships, west of the known meridian, find township number 4 north,' in this range, and lastly, section number 6 of that township. The corners of the flections should be marked by permanent corner-posts, or by lines blazed on trees.

& The sections are divided into half sections, quarter sections, and even into eighths of sections. The following table shows the contents of a township, and its 8ubdivi« dons:

1 township = 86 sections = 23040 acres.

1 section = 640 acres.

I section = 820 acres.

I section = 160 acres.

I section = 80 acres.

VARIATION OF THE NEEDLE.

7. The angle which the magnetic meridian makes with the true meridian, at any place on the surface of the earth, is called the variation of the needle at that place, and is east or west, according as. the north end of the needle lies on the east or west side of the true meridian.

8. The variation is different at different places, and even at the same place it does not remain constant for any length of time. The variation is ascertained by comparing the magnetic, with the true meridian.

9. If we suppose a line to be traced through those pomts on the surface of the earth, where the needle points directly north, such a line is called the line of no variation. At all places lying on the east of this line, the variation of the needle is west; at all places lying on the west of it, the variation is east.

10. The public is much indebted to Professor Loomis, for the valuable results of many observations and much scientific research, on the dip and variation of the needle, contained in the 89th and 42d volumes of Silliman's Journal.

The variation at each place was ascertained for the year 1840; and by a comparison of previous observations and the application of known formulas, the annual motion, or change in variation, at each place, was also ascertained, and both are contained in the tables which follow.

11. If the annual motion was correctly found, and continues uniform, the variation at any subsequent period can be ascertained by simply multiplying the annual motion by the number of years, and adding the product, in the algebraic sense, to the variation in 1840. It will be observed that all variations west are designated by the plus sign ; and all variations east, by the minus sign. The annual motions being all west, have all the plus sign.

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