352 



Popular Science Monthly 



Surveyors climbing to the top of a precipi- 

 tous cliff in Alaska to take observations 



Risking Lives for the Sake of Pre- 

 cision in Government Surveys 



ONE of the most difficult and exacting 

 tasks of an extensive land survey 

 made by the United States Coast and 

 Geodetic Survey, is the selection of points 

 from which observations may be taken. In 

 heavily wooded country it is necessary to 

 climb the tallest trees or to raise poles 

 taller than the trees, from which the distant 

 horizon can be seen and such observations 

 made as may be practicable. In 

 mountainous country such as Alaska 

 the surveyors have to face death 

 for the sake of precision, 

 climbing the highest peaks in 

 order to obtain an unob- 

 structed view of the hori- 

 zon. 



Why risk one's neck to 

 make a simple survey " 

 Because when great pre- 

 cision is desired it is im- 

 possible with chain or 

 tape to survey a region 

 in which there are bays, 

 rivers, mountains and 

 other natural obstruc- 



tions. To overcome these difficulties the? 

 method called "triangulation" is employed. 

 It rests upon the simple proposition taught 

 in every school that if one side and the 

 angles of a triangle are known the remain- 

 ing sides can be computed. It is to obtain 

 the first side of a triangle, or base line, that 

 the surveyors climb the highest trees and 

 mountains. So painstaking is their work 

 that in a survey of one hundred miles the 

 error is often less than five feet. 



The accompanying photograph shows a 

 Government surveying engineer climbing a 

 steep cliff in Alaska, prior to establishing 

 a base line. On his back he carries the 

 necessary surveying instruments. On the 

 top of the cliff stands a companion engineer 

 who undoubtedly scaled' the cliff without 

 assistance. The feat is made safer' for the 

 second man because of the rope which has 

 been lowered to guide him in his ascent of 

 the nearly perpendicular^ surface. 



If he is to measure a great distance from 

 the top of the cliff the only instruments the 

 engineer will use will be heliotropes (not 

 helioscopes) by day and powerful lights by 

 night. The heliotrope is a small mirror so 

 arranged that it reflects the sunlight in a 

 long line toward the observer. 



Keeping School Desks Presentable 

 with Cardboard Covers 



A 



The cardboard cover keeps the 

 school desks always presentable 



JANITOR of a school in 

 Pasadena, Cal., has found 

 way to keep the desks in 

 his classrooms looking 

 bright and presentable 

 without subjecting them to 

 frequent planing and var- 

 nishing. He slips over the 

 desk tops a pressed-card- 

 board cover, which he calls 

 an envelope. The enve- 

 lopes are made to conform 

 with the general shape of 

 the desk tops, and the 

 outer edges are bent down 

 and back and riveted, so 

 that the cover will slip on 

 over the desk top and will 

 remain in position after it 

 has been adjusted. 



There is a groove in- 

 dented at the top of the 

 cover to receiye pencils and 

 pens, and a circular open- 

 ing is provided through 

 which the inkwell shows. 



