Practical geodesy : comprising chain surveying and the use of surveying instruments, levelling and tracing of contours, together with sanitary surveys of towns, trigonometrical, colonial, mining and maritime surveying / by J. Butler Williams.

Williams, J. Butler (James Butler), Sir.

Date:: 1855

Credit: Practical geodesy : comprising chain surveying and the use of surveying instruments, levelling and tracing of contours, together with sanitary surveys of towns, trigonometrical, colonial, mining and maritime surveying / by J. Butler Williams. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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$however, that when one of these stations, thus appearing in the line, is very distant, there is no certainty of its extreme projection or lowest point being seen. This additional element of error may be avoided by having an observer on the look out at the mast-head, to give notice of the exact instant when he sees both the points in a line. The angles, measured are entered in the field-book, precisely in the same manner as those we have before described ; the soundings and the reckoning, and other re- marks, are entered in the field-book according to the form annexed. Time. Knots. FatUoms. Courses. Winds. Soundings. A.M. Fathoms. 2 At Anclior. W. 15 8 1 C) s.s.w. W. 4 2 s. 20 5 2 S. by W. 2.31 6 3 4 S.S.W. 20 7 2 s.w. N.W. 18i- 8 ] 1 E. by N. Tacked, 22| 9 1 4 E. W. 27 10 1 6 S.W. Tacked. 21 11 3 S.W. 19 12 3 S.W. 16i Remarks. Weighed, and stood to A. Measuring Distances by Sound. Sound, as a means of ascertaining great distances approximately, is not to be neglected. Its velocity, as ascertained by the latest experiments,* may be assumed at 1089, or in round numbers 1090 feet per second of time ; a watch, therefore, by which an observer can measure with accuracy fractions of seconds, will enable him to determine * Phil. Trans., 1824. Dr.'Moll's Account of the Experiments on the Velocity of Sound. . ^/^/^' ^^^^J^ \$