SAVING LABOR IN MEASURING HEIGHTS 



A New Principle Applied to the Hypsomcter 



By S. B. Detwilrr 



Those who have used the standard hypsometers are aware that 

 severe eye and neck strain accompany their use, especially in the 

 type of instruments with small sighting apertures. There is little 

 inconvenience in sighting a gun because of well-constructed 

 sights and the elimination of annoying unsteadiness caused by 

 weight poorly distributed. If the principle used in sighting a 

 gun is applied to the hypsometer, valuable time and nervous 

 energy will be saved. 



The easiest sighting surface for a hypsometer is a straight- 

 edge. The difficulty occasioned by unsteadiness in holding the 

 instrument may be overcome by dividing the sighting surface into 

 a fixed part and a movable or adjustable part. The fixed sight 

 maye be merely a flat brass strip, or it may be the top of a sight- 

 ing board (Fig. 1) such as an army sketching case or a tally 

 board. The adjustable arm is a strip of light brass, or a rod, 

 which is pivoted to the fixed sighting surface at the end nearest 

 the eye of the operator, and is held parallel to the edge of the 

 fixed surface by a spring which may be released at will. The 

 adjustable arm is counter-balanced back of the pivot, so that the 

 arm balances evenly on the pivot when the spring is released. A 

 heavily weighted pendulum is suspended from the same pivot as 

 the movable arm, and attached to it is an arc of sheet brass which 

 is slotted so as to move freely through a thumb screw fastened 

 to the adjustable arm about 2 inches from the pivot. With the 

 fixed and adjustable sighting surfaces held parallel and the thumb 

 screw free, the instrument is sighted at the base of the tree. 

 After the weighted pendulum has swung forward and is at rest, 

 perpendicularly, the thumb screw is tightened to bind the arc of 

 the pendulum to the adjustable arm, and the spring holding the 

 end of the arm is released (Fig. 2). No matter how much the 

 sighting board may be moved after this operation, so long as the 

 operator remains in the same position, the adjustable arm re- 

 mains sighted on the base of the tree, being held thus by the 

 action of the weighted pendulum. 



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