CHAPTER XIX 



MISCELLANEOUS 



Distortion of Printed Charts — Sailing Directions— Observations on Under- 

 currents — Pillsbury Current Meter — Exploring a Paver — Swinging Ship. 



In printing charts from an engraved plate, the paper has to Distortion 

 be damped. This results in distortion on the sheet drying, chart^.*^^^ 

 and angles laid off on a published sheet will never be found 

 to agree exactly, especially if the sheet is large. This must 

 always be borne in mind, in trying angles on a published 

 chart. 



For this reason, when a published plan is to be examined, 

 a dry " proof " is supplied to the surveyor from the Admiralty. 

 This is an impression " pulled," as it is termed, on to a dry 

 sheet. It is much fainter than a damp-pulled copy, and would 

 not do for ordinary use ; but being an exact facsimile of the 

 copper plate, all angles, bearings, etc., should agree precisely, 

 if the original survey is correct. 



This fact of the distortion of published charts is not gener- 

 ally known, and many reports of so-called inaccuracies have 

 been made in ignorance of it. The amount of it varies with 

 the goodness of the paper, and the trouble bestowed by the 

 printer in damping his paper uniformly. It is a fact much 

 to be deplored, and the man who invents a means of obviating 

 it will bestow a great boon on cartography. 



No survey is complete unless accompanied by sailing direc- Sailing 

 tions. Notes for these should be continually accumulating fl^"'=- 

 during the course of the survey, and the directions themselves 

 should be completed immediately after the work in the field, 

 when every essential point is fresh in the memory. The instruc- 

 tions for writing sailing directions issued by the Hydrographic 

 Department, Admiralty, should be consulted. 



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