Book Description

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1916 edition. Excerpt: ...standard datum for geodetic operations in Canada and Mexico, it became a matter of international importance, and consequently its designation was changed by the Survey in 1913 to that of the " North American datum." Plans are now under way for carrying the primary triangulation of the United States and Canada to the Yukon, and the prediction is here made that eventually the 50 miles which separate Alaska from Siberia will be spanned and a junction be effected with the great systems of Asia, Europe, and Africa. Then, with the extension from Mexico through Central and South America, the data will be available for a " world datum," and the final word will l1ave been said in the geodetic work of the earth. BASE-LINE MEASUREMENTS Closely related to, and forming an integral part of the triangulation executed by the Coast and Geodetic Survey, is the measurement of the base lines for controlling the lengths in triangulation. In this work the Survey has furnished much of interest and of value to the geodesist. Ever has it kept keenly before it the necessity for refined measurements, and many valuable devices to accomplish this desired result have been added by members of the force. BASE BARS The Duplex bars, invented by Assistant William Eimbeck and constructed by E. G. Fischer, are probably the best form of base bars ever devised, and gave a very high degree of precision; but they were soon replaced by the tape as a form of base apparatus. The only bar used in the United States, and probably in the world, which gives entire satisfaction, so far as accuracy is concerned, is the iced bar, designed by President R. S. Woodward, of the Carnegie Institution, when an assistant in the Survey. Owing to the great cost per kilometer...