54 A MANUAL FOR NORTHERN WOODSMEN 



the telescope to a horizontal position; five chains north of the 

 place of observation set a stone or drive a firm peg, upon which 

 by a strongly illuminated pencil or other slender object, exactly 

 coincident with the vertical wire, mark a point and drive a tack 

 in the line of sight thus determined; then, to eliminate possible 

 errors of collimation or imperfect verticality of the motion of the 

 telescope, quickly revolve the vernier plate 180, direct the glass 

 at Polaris and repeat the observation ; if it gives a different result 

 find and mark the middle point between the two results. This 

 middle point, with the point marked by the plumb bob of the 

 transit, will define the trace of the vertical plane through Polaris 

 at its eastern or western elongation, as the case may be. 



By daylight lay off to the east or west, as the case may require, 

 the proper azimuth taken from the following table (page 56) ; the 

 instrument will then define the meridian. The needle may be 

 read then, giving the magnetic declination, east or west as the case 

 may be. Or the line may be permanently marked for reference 

 at another time or with another instrument. 



To DETERMINE A MERIDIAN WITHOUT A TELESCOPE 



Attach a plumb line to a support situated as far above the 

 ground as practicable, such as the limb of a tree, a piece of board 

 nailed or otherwise fastened to a telegraph pole, a house, barn, 

 or other building, affording a clear view north and south. 



The plumb bob may consist of some weighty material, such as 

 a brick, a piece of iron or stone, weighing four to five pounds, 

 which will hold the plumb line vertical, fully as well as one of 

 finished metal. 



Strongly illuminate the plumb line just below its support by a 

 lamp or candle, care being taken to obscure the source of light 

 from the view of the observer by a screen. 



For a peep sight, cut a slot about one-sixteenth of an inch wide 

 in a thin piece of board, or nail two strips of tin, with straight 

 edges, to a square block of woqd, so arranged that they will stand 

 vertical when the block is placed flat on its base upon a smooth 

 horizontal rest, which will be placed at a convenient height south 

 of the plumb line and firmly secured in an east and west direction, 

 in such a position that, when viewed through the peep sight, Po- 

 laris will appear about a foot below the support of the plumb line. 



The position may be practically determined by trial the night 

 preceding that set for the observation. 



About thirty minutes before the time of elongation, as obtained 

 from the table, bring the peep sight into the same line of sight with 

 the plumb line and Polaris. 



To reach elongation, the star will move off the plumb line to 

 the east for eastern elongation, or to the west for western elonga- 

 tion ; therefore by moving the peep sight in the proper direction, 

 east or west, as the case may be, keep the star on the plumb line 

 until it appears to remain stationary, thus indicating that it has 

 reached its point of elongation. 



