NATURE 



169 



THURSDAY, DECEMBER 20, 



MERRIFIELD'S " TREA TISE ON 



NA VIGA TION " 



A Treatise on Nn'i'i«ation for the Use of Students. By 



John Merrifield, LL.D., F.R.A.S., F.M.S. (London: 



Longman and Co., 1SS3.) 



THE autlior of this volume having been engaged for 

 many years in preparing candidates for the different 

 examinations into which navigation enters, has felt the 

 want of a text-book embracing all that the different 

 examining boards embody under that head, and has 

 endeavoure'l, and we think successfully, to supply that 

 want by the present treatise. 



The work, although entitled "A Treatise on Naviga- 

 tion," deals only with one part, viz. that particularly 

 relating to what is generally known under the name of 

 dead reckoning, and does not touch on astronomical 

 observation, which we presume Mr. Merrifield classes 

 under the head of nautical astronomy, but which is really 

 the most important part of navigation. The title there- 

 fore is somewhat misleading. Neither do we agree with 

 the author's definition of theoretical and practical navi- 

 gation ; what Mr. Merrifield terms practical navigation, 

 viz. the management of the ship, making and shortening 

 sail, steering, &c., is usually known as seamanship. The 

 theory of navigation is surely the proving that by the 

 application of certain problems the particular position 

 occupied by a vessel can be accurately ascertained ; 

 whilst the practice is the actually finding the ship's place 

 by means of the instruments necessary to give the data 

 required by the theory. 



But although some small points in the work may be 

 selected which may perhaps offend the practical navi- 

 gator confident in his own ability, and consequently too 

 much inclined to look down on the instructions of school- 

 men, to whom he is far more indebted than he is generally 

 disposed to admit, to the student this work will be found 

 most useful : the chapters are well arranged, the exercises 

 at the end of each chapter are pertinent to the preceding 

 text, and require him to digest the text in order to answer 

 them satisfactorily. We propose, however, to offer some 

 remarks and suggest some additions which the author 

 may perhaps consider should another edition of his work 

 be required. 



In the description of the compass one type only has 

 been selected — that in use in the mercantile marine. No 

 account is given of the instruments used in the navy or of 

 Sir William Thomson's invention. This is certainly a 

 defect in the work, as if one instrument can be considered 

 as of more importance than another, in the navigation of 

 a vessel, it is the compass. Without it, notwithstanding 

 all the other improvements which have taken place in 

 navigation, we should be in much the same position as 

 the seamen of old, who were afraid to venture out of 

 sight of land. In fact we have always thought that the 

 education of naval men so far as regards the compass, 

 and magnetism generally, has been very much neglected, 

 and its vast importance has hitherto not received that 

 attention, in treatises on navigation, it deserves. Mr. 

 Vol. XXIX. — No. 738 



Merrifield has made a great stride in advance, as he 

 treats, in his ninth chapter, of the coefficients and the 

 means of correcting the compass for the local attraction 

 of the ship. This is a subject of great importance in the 

 present day : all navigators should be able to adjust their 

 own compasses, and should have the means of doing so 

 at their disposal, as a compass might be disabled in any 

 vessel, and in war-ships, particularly, a general action 

 might cause the loss of the correcting magnets of every 

 vessel in the squadron, when, unless some officer on 

 board could replace them, and correct the compasses, the 

 fleet might be placed in a most critical position, more 

 especially in thick weather or when entangled amongst 

 shoals. We doubt if the latter contingency has yet excited 

 any attention, yet its importance will be at once seen if 

 we suppose that one ship only in a squadron has had her 

 compass disabled in action and that subsequently thick 

 weather prevails. Such a ship endeavouring to obey the 

 signals of the admiral might either fall into the enemy's 

 hands or by fouling vessels in her own squadron tem- 

 porarily render them unfit to renew the engagement. 



Whilst considering this contingency, it might perhaps 

 be as well to draw attention to the fact that, in addition 

 to our ironclads, many large steam-vessels are now fitted 

 with sirens in place of the ordinary steam-whistle. It 

 would therefore seem expedient that some definite means 

 should be enforced to prevent their signals being mistaken 

 for the sirens sounded in foggy weather from lighthouses 

 and lightships. 



In describing the mode of correcting the compass for 

 the effect of local attraction no notice is taken of the 

 method of doing so by a single magnet — often adopted in 

 the navy. We are, however, glad to see that Mr. Merri- 

 field refers the student to the works of Sir George Airy 

 and Sir Frederick Evans, to both of whom sailors owe a 

 debt of gratitude. That we are able to navigate our large 

 iron ships and armour-plated vessels with the same facility 

 as the old wooden ships of the past is due almost entirely 

 to their labours, combined with those of the late Archibald 

 Smith, F.R.S. 



In the chapters on the various methods of finding the 

 position of a ship by dead reckoning, known as the 

 "sailings," we do not find much improvement on the 

 works of the older writers except in one particular — 

 Mercator's sailing. This, which is the most accurate 

 method of dead reckoning, is treated of in a separate 

 chapter, and the formula for calculating the meridional 

 parts for the spheroid, as well as the sphere, is now for 

 the first time published in " A Treatise on Navigation," 

 the only work of the sort in which we remember to have 

 seen it before being Galbraith's " Surveying." It is true 

 that Riddle, in a note, refers the student to Gauss's 

 paper, published in the Philosophical Magasine for 1828, 

 and Mendoza y Rios, in his tables, gives the meridional 

 parts for the spheroid as well as the sphere, but does not 

 say what compression he used in the calculation : Mr. 

 Merrifield, however, seems to be the first to give the 

 subject that prominence in "A Treatise on Navigation" 

 we think it deserves, more especially now when the 

 steamers running from England to the United States are 

 reaching the extraordinary rate of 450 miles a day, and it 

 is no unusual thing to be two or three days without ob- 

 taining astronomical observations. It therefore becomes 



