International Correspondence Schools · Scranton, Pa. : The Colliery engineer co. · leaf 372
ing 240.5 feet, the roof gradewill be 240.5 feet + 24 feet (the height of the tunnel section)which is 264.5 feet. As the height of instrument is 259.6feet, the rod-reading for roof grade will be 2(i4.5 — 259.6 =4.9 feet. A common bulls-eye lantern is used to illuminatethe cross hairs, and a small… … Fig. 453.tion and measuring up the work. The best device is thefollowing, shown in Fig. 453. A semi-circular protractorA B oi 2L diameter from 8 to 10 feet, and made of light pine, 962 RAILROAD CONSTRUCTION. is set up at right angles to the center line of the tunnel.The diameter A B of the…
Railroad engineering
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