438 Forestry Quarterly 



This principle may be applied to topographic mapping by the 

 use of a metal ruler of any convenient size, suspended at one 

 end on a pivot of small diameter. The instrument constructed 

 by the writer (Fig. 1) is of sheet brass, 1/16 inch thick, 1 inch 

 wide and 1 foot long, but a smaller size will be more convenient. 

 The pivot must be centered so that a line drawn lengthwise 

 through the center of the brass strip is a plumb line when the 

 ruler hangs free on its pivot. A pivot specially constructed on the 

 principle of a hub and axle will insure freedom of movement 

 and accuracy. One end of the pivot is tempered and sharpened 

 to a pin point, so that it will hold the instrument when driven 

 into the face of a sketching board. The pivot must permit the 

 ruler to swing freely parallel to the face of the board, but should 

 not allow much movement at right angles to it. The pivot end of 

 the ruler should be rounded or pointed so that the pin point may 

 be inserted exactly at the desired spot. The ruler is divided 

 lengthwise by a narrow slot sawed through the middle from the 

 pivot to within an inch of the opposite end. The edges of the 

 slot are bevelled on the face of the ruler and at the bottom of the 

 slot they are smooth and straight. The slot should be about 1/16 

 inch wide, so that a well-sharpened pencil point will easily reach 

 to the face of the sketching board beneath the ruler and move 

 freely in drawing a straight line the length of the slot. 



The top of the pivot may be a slotted sight on the order of a 

 compass sight, or a brass post with or without a ring sight. In 

 any case, the upper part of the pivot acts as a handle to drive 

 the pin point into the sketching board. The pivot point should 

 have a shoulder of about 1/32 inch to keep the ruler from being 

 jammed too tightly against the board. At the opposite end of 

 the slot another slotted sight or sighting pin is provided, so that 

 the ruler may be used as an alidade, similar to that used with a 

 traverse board, when the sketching board is held horizontally. 

 This feature of the profile alidade will make the use of the army 

 sketching board much more convenient and accurate. A scale 

 should be marked on the edge of the slot of the profile alidade. 



To use this instrument for obtaining grades and elevations, 

 the sketching board must have a straight edgt for a sighting 

 surface. Cross-section paper is fastened to the board so that the 

 lines are exactly parallel and perpendicular to the sighting edge. 

 A line is then drawn perpendicular to the sighting edge for 



