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a section.

The sections of a township are numbered from

1 to 36, beginning at the north-east angle, and each contains 640 acres.

The diagram exhibits the 36 sections of a township.

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To describe a section accurately, we say, section number 5, in township number 4 north, in range 3d west of a known meridian; the one, for example, drawn through the mouth of White river. The description fixes precisely the place of the section. Go to the 3d range of townships, west of the known meridian, find township number 4 north, in this range, and lastly, section number 5 of that town. ship. The corners of the sections should be marked by permanent corner-posts, or by lines blazed on trees.

6. 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 subdivisions:

1 township 36 sections=23040 acres.

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= 640 acres.

section=320 acres.
section = 160 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 points 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 39th 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 ob served that all variations west are designated by the plus sign; and all variations east, by the minus sign. The an

12. Our first object will be to mark the line, as it was in 1840, of no variation. For this purpose we shall make a table of places lying near this line.

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At the point whose latitude is 40° 53', longitude 80° 13', the variation of the needle was nothing in the year 1840, and the direction of the line of no variation, traced north, was N 24° 35' west. The line of no variation, prolonged, passed a little to the east at Cleveland, in Ohiothe variation there being 19 minutes east. Detroit lay still further to the west of this line, the variation there being 1° 56' east; and Mackinaw still further to the west, as the variation at that place was 2° 08′ east.

The course of the line of no variation, prolonged southerly, was S 24° 35′ E. Marietta, in Ohio, was west of this line the variation there being 1° 24′ east. Charlottesville, in Virginia, was a little to the east of it-the variation there being 19' west; whilst Charleston, in South Carolina, was on the west, the variation there being 2° 44' east.

From these results, it will be easy to see about where the line of no variation is traced in our own country.

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