June 29, 1882] 



NATURE 



195 



inscriptions that even the Deir-el-Bahari find is not to 

 compare with the inscriptions on the temples of Denderah 

 and Edfu, and those of the caves of Siut. 



HYDROGRAPHICAL SURVEYING 

 Hydrographical Surveying; a Description cf the Means 

 and Methods employed in constructing Marine Charts. 

 By Capt. W. J. L. Wharton, R.N. (London : Murray, 

 1882.) 



CAPT. WHARTON, who has had considerable ex- 

 perience in nautical surveying, having been in 

 command of surveying vessels for nearly ten years, has 

 devoted his time, during the short interval he has been 

 unemployed, to writing a work on this part of the naval 

 profession which he modestly describes, in his preface, 

 as an endeavour to collect together information, which 

 has existed for years in a traditionary form amongst sur- 

 veyors, for the benefit of young officers who may wish to 

 devote themselves to surveying work in the future. 



A book of this sort was certainly much needed as since 

 the time of Sir Edward Belcher, only one treatise has 

 been written by a naval surveyor — Capt. R. Mayne, R.N., 

 C.B.— and we think Capt. Wharton deserves the thanks 

 of the profession for his exertions, and we hope to see 

 his work adopted as the text-book for instruction at the 

 Royal Naval College. 



Before however reviewing Capt. Wharton's treatise 

 we propose to state briefly what we consider to be the 

 requirements of a nautical survey. 



The perfection of marine surveying appears to us to be 

 the representation in a graphic form, readily understood, 

 of the coasts and harbours of the world with their various 

 off-lying dangers ; marking distinctly the various features 

 of high and low water lines, showing the dangers to be 

 avoided and the channels available for navigation, placing 

 prominently on the chart those objects on the land which 

 serve best to ascertain the position of a ship, and subor- 

 dinating all other features to these objects, so that the 

 channels to be used, and the marks by which those 

 channels can be recognised, are easily distinguished ; as 

 well as representing the set of the tides and currents and 

 the errors of the compass. To execute such a survey it 

 is evident considerable care must be bestowed in ascer- 

 taining accurately the positions of the land marks, as on 

 these depend the whole of the work, but this accuracy 

 need not be carried to such a degree of minuteness that it 

 cannot be shown on the chart ; for, after all, the principal 

 object of a chart is to show the soundings ; and enough 

 care has been bestowed on the land-marks if their posi- 

 tions are ascertained with sufficient precision for sound- 

 ings. Of _ course circumstances occasionally arise when, 

 from other causes, it may be advisable to modify this 

 arrangement, but not for the purpose of navigation. 



Capt. Wharton appears to have kept these objects 

 steadily in view in writing his work. The work com- 

 mences with a description of the instruments used in 

 nautical surveying, which, although previously given by 

 Heather and by Simms, cannot be considered out of place, 

 and then gives a description of marine surveying in general 

 afterwards entering into particulars. We regret that in 

 the description of the sextant the important errors of 

 centering and graduation have been overlooked. 



We much commend the following remark at p. 54, too 

 often ignored by surveyors : — " The accuracy necessary 

 in many details of a chart depends very much upon its 

 scale. Over-accuracy is loss of time. Any time spent in 

 obtaining what cannot be plotted on the chart is, as a 

 rule, loss of time." 



Of course the scale on which a survey should be exe- 

 cuted should be settled after due consideration. It is 

 evident that an inaccessible coast, off which there is deep 

 water, does not require the same accuracy of delineation 

 as a coast studded with bays and harbours, or off which 

 numerous dangers exist ; or those portions of the globe 

 little frequented by shipping the same care as the coasts 

 of the United Kingdom. These points must to a great 

 extent be left to the officers in charge of a survey, but the 

 scale once settled no time should be wasted over details 

 which cannot be shown on that scale, 



Capt. Wharton's remarks on soundings are excellent. 

 There is no doubt that this, the most important work of 

 the marine surveyor, is very monotonous. To sit in a 

 boat day after day, from early morn to dewy eve, marking 

 in a book soundings and angles, with the salt from the 

 spray drying up one's skin, and the sun blistering one's 

 nose requires more than ordinary zeal, patience, and per- 

 severance ; and only long practice enables the surveyor to 

 really take an interest in this work. Young surveyors 

 should, however, remember, that every other detail is 

 subordinate to this, and that until they can really sound, 

 thoroughly, over a given patch of ground without loss of 

 time they cannot be considered masters of the profession. 



Capt. Wharton's remarks on obtaining latitudes and 

 running meridian distances are excellent. We think 

 indeed that, in the latitude, the same results might be 

 obtained with less figures, but it is by no means easy to 

 draw a hard and fast line. 



In the remarks on tides, no mention is made of the 

 importance of referring the result obtained to a fixed 

 mark on the shore, nor any observation as to the diurnal 

 inequality, and consequently the necessity of, on all 

 occasions, when practicable, registering both day and 

 night tides. In the Eastern Archipelago the diurnal 

 inequality is in some places 4 to 5 feet, and in Australia 

 the mean tide level also differs at different times. These 

 facts appear to have escaped Capt. Wharton's notice, but 

 probably will be inserted in another edition. 



In the rermrks on searching for Vigias, and ascertain- 

 ing the position of a ship at sea, Capt. Wharton seems to 

 think accurate observations cannot be obtained, as he 

 asserts the position of a ship to be doubtful to three 

 miles. 



On this point we must differ from him, as long experi- 

 ence has proved, to our own satisfaction, that provided 

 the weather is fairly clear the position of the ship can be 

 obtained to half a mile. Nor in asserting this do we rest 

 on single evidence, as Capt. Moriarty, R.N., C.B., in the 

 Great Eastern, had no difficulty in picking up the end of 

 the Atlantic cable when it had been slipped from the 

 ship. 



The fact is the great error in sea observations is due to 

 the refraction of the horizon, but it must be borne in mind 

 that, excepting in shallow water, this is but slight, and 

 that it can always be corrected by observing on opposite 

 sides of the horizon. 



