Popular Science Monthly 



Range-Finder to Locate Landmarks 

 and Signal Fires 



WE NATURALLY think of a range- 

 finder as that part of a gunner's 

 equipment which tells him the distance to 

 his target, thus enabling him to give the 

 proper elevation to his gun. But the 

 range-finder off the battlefield is a part of 

 the equipment of a tramping kit which 

 will tell the width of valleys and rivers and 

 the distances to landmarks and signal fires. 



until the two inside edges of the images are 

 parallel to the thin edge of the wedge. 

 When the one image-edge is in line with 

 the wedge's thin edge, the image-edge in 

 the other mirror should also be in line with 

 it. The image positions should appear as 



A range-finder suitable for the woodsman or camper to aid in locating landmarks and computing 

 their distances or the width of rivers and valleys. It is made of odds and ends of scrap 



Any boy can make his own range finder 

 from materials that might otherwise go to 

 the scrap-heap. 



The essential feature of the device is 

 shown at A. This is cut from a wedge- 

 shaped piece of wood 2 in. long, 1*4 in. 

 wide, and 3/32 in. thick. From the thick 

 end it is tapered to a very thin edge at the 

 other end. Cut away a piece }^-in. wide 

 extending from the thin end to J^ the way 

 toward the thick end. 



Two strips 2> l A in. long and J^ in. wide 

 are cut from a good quality of thin mirror, 

 and they are fastened to the prepared 

 wedge of wood with bits of beeswax. Both 

 mirrors face toward the front as shown. 



Lay the mounted mirrors face-up on the 

 floor, slipping something under one side of 

 the wedge so that the lower mirror will be 

 level. Cut from stiff white paper a piece 

 exactly 2 in. square, then hold it in a 

 horizontal position just 20 in. above the 

 thin edge of the wood wedge, peering down 

 at the mirrors through a hole punched in 

 the center of the paper square. 



Two images of the card will be seen, one 

 in each mirror. Slip the card along, keeping 

 it 20 in. from the wedge-edge, rotating it 



indicated by the shaded portions in the 

 mirrors. If, however, the images overlap, 

 then the mirror strips are too nearly 

 parallel; if they do not touch, then the 

 angle between the mirrors is too great. In 

 either case the angle between the mirrors 

 must be corrected by pressing the mirror 

 strips firmly against their beeswax pellets 



A wedge shaped piece of wood with thin mir- 

 rors attached is fastened to a baseboard 



until they fulfill the alinement test at the 

 20-in. distance. A little patience is needed. 

 When successful take a stick of red sealing 

 wax and a hot nail and wax the edges of the 



