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FOR PRACTICAL 

 WORKERS 



A Chemical Preparation to Preserve 

 Cut Flowers 



IF a little saltpeter, or carbonate of 

 soda, is added to the water in which 

 flowers are left standing, they can be 

 kept comparatively fresh for more than 

 two weeks. Another method is to add a 

 small amount of ammonium chloride, or 

 camphor, to the water. The presence of 

 one of these substances stimulates the 

 plant cells and acts in opposition to 

 germ growth. Flowers that have wilted 

 can be revived for a time if the stems are 

 inserted in a solution of weak camphor 

 water. — Herman Neuhaus. 



Simple Construction of a Useful 

 Range Finder 



ONE of the simplest range finders ever 

 devised consists of a short tube, 

 one end closed by a cap pierced with a 

 pin-hole, the other end covered with a 

 wire screen of square meshes. 



The manipulation is as simple as the 

 construction of the instrument. With the 

 eye close to the pin-hole, look through the 

 tube at some distant object of known 



The tube with its peep hole and screen cov- 

 ered end and formula to compute distances 



length (say a distant freight car). The 

 ware mesh will stand out clearly in the 

 field of view, and the number of spaces 

 which are outlined against the object 

 may be readily counted off. (In the 

 accompanying illustration the tower is 



six spaces high.) It is evident that the 

 object is farther from the peep-hole than 

 the wire mesh, in the same ratio as the 

 length of the object is to the aggregate 

 width of screen openings which enclose it. 

 (See preceding diagram). Suppose a 50-ft. 



In looking through the range finder the 

 object is covered with the mesh screen 



freight car is covered by four spaces of a 

 20-wire-to-the-inch screen. The distance 

 to the car is obtained by multiplying the 

 length of the range finder by the ratio of 

 50 ft. to 4/20 of an inch, i. e., by the 

 ratio of 3000 to 1. If the range finder is 

 2 ft. in length, the car is two thousand 

 yards distant. 



It is plain that this type of range 

 finder is restricted to use with objects of a 

 knowTi dimension. The height of a 

 distant man may be taken as 70-in., with 

 a probable resulting error of less than 

 5 per cent. Objects of a fairly standard 

 length should be chosen. Recording to 

 fifths of a screen space is comparatively 

 easy. Even a novice may determine 

 ranges with an error not exceeding 10 per 

 cent. 



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