PliEFACE TO THE THIRD EDITION 



The lamented death of Rear-Admiral Sir William Wharton, 

 K.C.B,, F.R.S., having occurred since the publication of the 

 last edition of ' Hydrographical Surveying,' at the request of 

 the publisher I have undertaken the preparation of a new 

 edition, rendered necessary by lapse of time and improvements 

 effected in various directions. 



Material alteration in the text of the former edition has been 

 avoided as far as possible, but the work has been enlarged by 

 the addition of some new- features, including expedients 

 connected with work in the field which have been found useful 

 in practice. Most of these are, no doubt, familiar to the 

 experienced surveyor, but they are not so obvious to younger 

 officers unless their attention is called to them. Amongst 

 other fresh matters referred to in this edition, the following 

 may be mentioned : The use of photography for the reproduc- 

 tion of chart drawings on smaller scales, and the special style 

 of drawing consequent thereon ; the introduction of chrono- 

 graphs for use in the field ; the development of the Pillsbury 

 deep-sea current meter ; a new form of automatic tide-gauge, 

 and its possibilities for use in deep water ; the application of 

 the range-fmder to surveying purposes ; an improved slipping 

 apparatus for ship sounding ; and the practical effect of better 

 knowledge of the nature of the slope of the bottom at different 

 depths in connection with searching for vigias. 



To officers in charge of surveys, it is hoped that the examples 



