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To find the Elongation of this Star in any Latitude, its Declination must be known ; that is, its distance North of the Equator. This being found, institute the following Proportion :

As Co-Sine of the Latitude ; Is to Radius ; So is Co-Sine of the Declination ; to Sine of the Elongation.

From a Table in Blunt's Practical Navigator it appears that the Declination of the North Star, January 1, 1800, was 88° 14' 32", and increasing at the rate of_19.69 Seconds annually. Consequently, January 1, 1805, the Declination will be 88° 16' 10", and the Co-Declination or Polar distance will be 1° 43' 50."

According to the above Proportion, the Elongation, January 1, 1805, in Lat. 41° 30' will be 2° 18' 39", and in Lạt. 42° it will be 2° 1944".

The following Table shows the Elongation in several different Latitudes for five years successively. It is calculated for the first of January in each year; and in using it, if the time when the Elongation is required, be past the middle of the year, take it for the beginning of the next year.

A Table showing the Elongation of the North Star.

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13.9° 30'2014' 35" 20 14' 10" 2° 13' 44" 2° 13' 19" 2° 12' 53"

40

2 15 34 12 15

8 12 14 43 12 14 17 12 13 52

40 30 12 16 34 12 16

8 12 15 42 12 15 17 12 14 51

41

2 17 36 2 17 10 2 16 4.4 2 16 18 2 15 52

41 30 2 18 39 2 18 13 12 17 47 12 17 20 2 16 54

42

2 19 44 2 19 18 12 18 51 12 18 25 2 17 58

42 50 12 20 51 2 20 24 12 19 58 12 19 31 2 19

5

43

2 22

0 12 21 33 12 21

6 12 20 40 2 20 13

43 30 12 23 10 12 22 43 12 22 16 12 21 49 2 21 22

The Elongation for the Latitude of the observation being calculated, or taken from the above Table, proceed to find its range, according to the following directions :

Take a pole 18 or 20 feet in length ; to the end of it fasten a small line ; raise it to an elevation of 45° or 50°; and support it by two crotches of a suitable height to keep it firm in its place. At the end of the line, near the ground, fasten a weight of half a pound or more, which should swing in water to prevent the air from moving the line. Southward of the line, fix a Compass sight, or other piece of metal or wood, with a narrow, perpendicwiar aperture at a convenient height from the ground, say about 2

distance East or West at pleasure. Let an assistant hold a light either NE. or NW. of the Line, nearly as high as the range from the sight to the North Star, in such a position that the line may be plainly seen ; then, (the three Stars above mentioned being parallel or nearly so with the Horizon) move the sight-vane East or West, until through the aperture, the line is seen to cut the Star ; and continue to observe, at short intervals, till the Star is seen at its greatest Elongation. Let a lighted candle be placed in an exact range with the sight-vane and line at the distance of 20 Rods or more, which should stand perpendicularly, be made fast, extinguished and left till morning. Then the sight-vane, the line and the candle will be the range of Elongation, which observe accurately with a Compass; and if the Elongation be East and the Variation West, the former must be subtracted from the latter ; but if they are both West they must be added, and their difference or sum will be the true Variation.

Of the ATTRACTIOn of the NEEDLE.

IT
T is well known that any Iron substance has an influence uponi

the magnetic Needle, attracting it one way or the other from the point where it would settle were there no such attraction. A Surveyor should therefore be careful to see that no Iron is near the Compass when taking a Bearing. But as the Earth in certain spots contains, near its surface, Iron or other minerals which attract the Needle, it will frequently happen that it will point wrong. To ascertain whether this is the case, the Surveyor, at each station, should take a back view of the one last left ; and if he finds that the Compass does not reverse truly, he may be sure, provided the Compass be accurately graduated and placed horizontally, that he either made a mistake at the last station, or that in one or the other of the stations, the Needle was attracted from the true point. When he finds a place where he suspects there is an attraction he should go a few rods backward or forward, and see whether the Needle points differently. In this way he may prevent making mistakes in his Field notes, by putting down a wrong course. To take back sights is particularly necessary in running long Lines, and laying out new Lands; where the Needle is the only thing to guide the Surveyor.

By practice and experience a knowledge will be acquired on this subject, and with regard to many other things in Surveying, which cannot be taught by Books ; and after all the directions which can be written the Practitioner will frequently find occasion

To find the Elongation of this Star in any Latitude, its Declination must be known ; that is, its distance North of the Equator. This being found, institute the following Proportion :

As Co-Sine of the Latitude ; Is to Radius ; So is Co-Sine of the Declination ; to Sine of the Elongation.

From a Table in Blunt's Practical Navigator it appears that the Declination of the North Star, January 1, 1800, was 88° 14' 32", and increasing at the rate of 19.69 Seconds annually. Consequently, January 1, 1805, the Declination will be 88° 16' 10", and the Co-Declination or Polar distance will be 1° 43' 50."

According to the above Proportion, the Elongation, January 1, 1805, in Lat. 41° 30' will be 2° 18' 39", and in Lạt. 42° it will be 2° 19' 44".

The following Table shows the Elongation in several different Latitudes for five years successively. It is calculated for the first of January in each year; and in using it, if the time when the Elongation is required, be past the middle of the year, take it for the beginning of the next year.

A Table showing the Elongation of the North Stær. Latitud. 1805 1806

1

1807 1808 1809 13 90 30' 2° 14' 35" 214' 10" 2° 13' 44" 2° 13' 19" 20 12' 53"

40

2 15 34 12 15

8 12 14 43 12 14 17 12 13 52

40 30 12 16 34 12 16

8 12 15 42 12 15 17 2 14 51

41

2 17 36 12 17 10 12 16 44 12 16 18 12 15 52

41 30 2 18 39 2 18 13 12 17 47 12 17 20 2 16 54

42

12 19 44 2 19 18 12 18 51 12 18 25 2 17 58

[blocks in formation]

43 30 2 23 10 12 22 43 12 22 16 12 21 49 2 21 22

The Elongation for the Latitude of the observation being calculated, or taken from the above Table, proceed to find its range, according to the following directions :

Take a pole 18 or 20 feet in length ; to the end of it fasten a small line; raise it to an elevation of 45° or 50°; and support it by two crotches of a suitable height to keep it firm in its place. At the end of the line, near the ground, fasten a weight of half a pound or more, which should swing in water to prevent the air from moving the line. Southward of the line, fix a Compass sight, or other piece of metal or wood, with a narrow, perpendicular aperture at a convenient height from the ground, say about 2

be

distance East or West at pleasure. Let an assistant hold a light either NE. or NW. of the Line, nearly as high as the range from the sight to the North Star, in such a position that the line may plainly seen ; then, (the three Stars above mentioned being parallel or nearly so with the Horizon) move the sight-vane East or West, until through the aperture, the line is seen to cut the Star; and continue to observe, at short intervals, till the Star is seen at its greatest Elongation. Let a lighted candle be placed in an exact range with the sight-vane and line at the distance of 20 Rods or more, which should stand perpendicularly, be made fast, extinguished and left till morning. Then the sight-vane, the line and the candle will be the range of Elongation, which observe accurately with a Compass; and if the Elongation be East and the Variation West, the former must be subtracted from the latter ; but if they are both West they must be added, and their difference or sum will be the true Variation.

Of the ATTRACTIon of the NEEDLE.

IT,

T is well known that any Iron substance has an influence upon

the magnetic Needle, attracting it one way or the other from the point where it would settle were there no such attraction. A Surveyor should therefore be careful to see that no Iron is near the Compass when taking a Bearing. But as the Earth in certain spots contains, near its surface, Iron or other minerals which attract the Needle, it will frequently happen that it will point wrong. To ascertain whether this is the case, the Surveyor, at each station, should take a back view of the one last left ; and if he finds that the Compass does not reverse truly, he may be sure, provided the Compass be accurately graduated and placed horizontally, that he either made a mistake at the last station, or that in one or the other of the stations, the Needle was attracted from the true point. When he finds a place where he suspects there is an attraction he should go a few rods backward or forward, and see whether the Needle points differently. In this way he may prevent making mistakes in his Field notes, by putting down a wrong course. To take back sights is particularly necessary in running long Lines, and laying out new Lands; where the Needle is the only thing to guide the Surveyor.

By practice and experience a knowledge will be acquired on this subject, and with regard to many other things in Surveying, which cannot be taught by Books ; and after all the directions which can be written the Practitioner will frequently find occasion

To find the Elongation of this Star in any Latitude, its Declination must be known ; that is, its distance North of the Equator. This being found, institute the following Proportion:

As Co-Sine of the Latitude ; Is to Radius ; So is Co-Sine of the Declination ; to Sine of the Elongation.

From a Table in Blunt's Practical Navigator it appears that the Declination of the North Star, January 1, 1800, was 88° 14' 32", and increasing at the rate of_19.69 Seconds annually. Consequently, January 1, 1805, the Declination will be 88° 16' 10", and the Co-Declination or Polar distance will be 1° 43' 50."

According to the above Proportion, the Elongation, January 1, 1805, in Lat. 41° 30' will be 2° 18' 39", and in Lạt. 42° it will be 2° 19' 44".

The following Table shows the Elongation in several different Latitudes for five years successively. It is calculated for the first of January in each year; and in using it, if the time when the Elongation is required, be past the middle of the year, take it for the beginning of the next year.

A Table showing the Elongation of the North Star. Latitud., 1805 1806 1 1807

1809 39° 30' 2° 14' 35" 2° 14' 10" 2° 13' 44" 2° 13' 19" 2° 12' 53"

1808

40

2 15 34 12 15

8 12 14 43 12 14 17 12 13 52

40 30 12 16 34 12 16

8 12 15 42 12 15 17 12 14 51

41

2 17 36 2 17 10 2 16 4.4 12 16 18 12 15 52

41 30 12 18 39 2 18 13 12 17 47 12 17 20 2 16 54

42

2 19 44 2 19 18 12 18 51 12 18 25 2 17 58

[blocks in formation]

43 30 2 23 10 2 22 43 2 22 16 12 21 49 2 21 22

The Elongation for the Latitude of the observation being calculated, or taken from the above Table, proceed to find its range, according to the following directions :

Take a pole 18 or 20 feet in length ; to the end of it fasten a small line; raise it to an elevation of 45° or 50°; and support it by two crotches of a suitable height to keep it firm in its place. At the end of the line, near the ground, fasten a weight of half a pound or more, which should swing in water to prevent the air from moving the line. Southward of the line, fix a Compass sight, or other piece of metal or wood, with a narrow, perpendiculur aperture at a convenient height from the ground, say about 2

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