March 1, 1887.] 



KNOW^LEDGE 



103 



vessel would gain not a few days only, but weeks, by 

 following the great circle track, supposing no icebergs 

 intervened, and that no storms arose in high southern 

 latitudes which, even though blowing in the right direction, 

 would be too fierce for ordinary sailing, or might even 

 dismast and disable the stoutest sea ci-aft. 



Even the most favourable great circle com-se, then, may 

 have to be modified in order to secure safety, which must be 

 the first consideration with all prudent ship-captains and 

 with all -(vise shipownei-s. For instance, the great circle 

 course from Cape Town to Melbourne would carry a 

 ship into about 58^ south latitude, as would also a great 

 circle couree round Tierra del Fuego to Cape Town. A 

 course from Dunedin to ^'alparaiso would pass into still 

 higher latitudes. These journeys would all be very 

 dangerous, a large portion of each being infested by 

 icebergs, and exposed also to storms so terrible that the 

 stoutest clipper could not hope to pass through them 

 with undipped wings. It would ill-profit a captain to 

 have shortened his journey a hundred miles or so, or 

 even to have secured favourable winds throughout the 

 whole of it, if half the journey had to be made under jury 

 rigging, and a large sum had to be expended to restore the 

 battered bulwarks, and replace the best sails torn from the 

 bolt rojies by the hun-icanes of the southern seas. The risk 

 of actual loss through collision with an iceberg, or by 

 foundering in some great storm, is great enough to be an 

 important consideration to the bravest masters, and if not 

 to all shipowners, to the wiser, and assuredly to all under- 

 writers. 



It is necessar}', then, to follow a coui'se designed to 

 combine the greatest possible advantage in regard to distance 

 and favourable winds with the least risk from icebergs and 

 storm. This is done by following what is called the com- 

 posite coui-se. Supposing, for example, a captain or ship- 

 owner decides that on the journey from Cape Town to 

 Melboui-ne no latitude higher than 50^ south shall be 

 touched, then the plan to be pursued is to travel on a great 

 circle course from Cape Town to touch the limiting latitude 

 pai'allel, and thence to travel along that pai-allel until the 

 point is reached where a great circle coui-se from Melbourne 

 to that latitude parallel would touch it. This was the 

 course pui-sued by the captain of the Australasia. Mr. Fronde, 

 after mistaken!}' remarking that the true great circle course 

 fi'om Cape Town to Adelaide would lie athwart the South 

 Pole proceeds : '" This way there is no passage ; we were 

 to keep within the ' roaring forties ; ' " and even so, though it 

 was the southern midsummer, and the nights but two hours 

 long, they had to prepare for the temperature of an English 

 winter. '■ The thick clothes must come out of our boxes 

 again," he says : " the fire will be relighted in the saloon ; 

 we may fall in with icebergs, and see snow upon our decks, 

 and then in three weeks we shall be again in tropical sun- 

 shine amidst grapes and tiowere." 



Here, however, I must correct a rather curious mistake 

 which appears in one or two treatises on navigation. It is 

 asserted that the shortest way of passing from any one place 

 to any other on the earth's surface, subject to the condition 

 that the track shall nowhere pass above a given latitude, is 

 not the composite course, but two grait circle courses 

 meeting on that point of the highest latitude parallel, which 

 has the same longitude as the point of highest latitude on 

 the actual gi-eat circle coui-se. For instance, the most 

 southerly point on the true great circle course from Cape 

 Town to Melbourne lies in longitude 84° east and latitude 

 58" south ; the composite course touches latitude SC south 

 about 12^' east, and leaves it about 98^ east ! Xow, the 

 ide:x which I describe as a •' curious mistake " consists in 

 supposing that a better course than the composite one would 



be to rim gre.at cu-cle-wise from Cape Town to latitude .50" 

 longitude 84° east, and thence also on a great circle to 

 Melbourne. This journey, compounded of two great circle 

 courses, would unquestiomibly be shorter than the com- 

 posite course compounded of two great circle courses and 

 one couree along a parallel. But it would cany the ship 

 ttvice outside the limiting latitude — viz., for a considei-able 

 distance on the west of the point where the two great circle 

 coui'ses meet, and for a still gi-eater distance on the east of 

 that point. 



Recognising the advantages of great circle sailing — (1) in 

 its simplest form where practicable ; (2) in the composite 

 coni-s2 where a simple great cii-cle course passes through 

 inconveniently high latitudes ; and (3) as judiciously com- 

 bined with due consideration of winds and currents, the 

 question naturally arises, Why do not all sea-captains seek 

 to obtain to the fullest possible extent the advantages which 

 this method of sailing offers ? Shipowners ought to be even 

 readier to adopt the principle of great circle sailing, since its 

 employment would diminish not only the length of ocean 

 journeys, but also sea risks and expenses. 



It need hardlj' be said that captains who are navigators 

 as well not only recognise the advantages of great circle 

 sailing, but avail themselves also of those advantages. But 

 it must be remembered that a large proportion of the 

 mastei-s of ships engaged in trade are unable to employ 

 any but the simplest methods of navigation. Accustomed 

 to rhumb sailing, they are not very willing to employ 

 methods which require either compliaited constructions 

 or more or less recondite calculations. I use the word 

 '•■ recondite " rather than " difficult," because the former 

 word corresponds with the real objection which many 

 skippers entertain against processes of calculation. If a 

 shipmaster knows that taking out certain numbers from 

 tables, and dealing with them according to certain formulse, 

 he ^\'ill get out his proper course at starting from any point 

 to reach a given port, he yet has the feeling that in adopting 

 the course so calculated he is, as it were, walking in the 

 dark. A wrong figure or a wrong sign, or some misunder- 

 stood tbrection, might have made the calculation work out 

 wrong, and the coui-se on which, confiding in it, he sets out 

 nun/ therefore be very for from the best. 



Thus, although Mr. Towson has pro^-ided a series of ad- 

 mirable tables for facilitating the practice of gi-eat circle 

 sailing and composite sailing, it is found that a large pro- 

 portion of the captains of ocean-going vessels care little 

 to avail themselves of these tables. Steamei-s may follow a 

 particular calculated track — though there are few steamers 

 as compared with sailing ships or auxiliary steamships on 

 the longer voyages to which the principles of great circle 

 sailing chiefly apply. But sailing vessels are often driven 

 far from the course which might be calculated, at starting, 

 as the best ; and once this has happened the calculations so 

 made are practically useless. 



On the other hand, Mercator's charts are so simple and a 

 rhumb line is so easily drawn, being simply a straight line, 

 that seamen are not gi-eatly attracted to the use of methods 

 requiring complicated constructions to obtain the required 

 course, or showing that course in a way not easily inter- 

 preted. For we must remember what the sailor wants, 

 and what, so far as the rhumb course is concerned, Mer- 

 cator's charts actually supply. He wants not only to know 

 through what latitudes and longitudes his voyage will airry 

 him, but to know at each point of his journey the bearing of 

 his course. Suppose, for instance, he has been driven otf the 

 track he had intended to follow, and finds himself in a certain 

 position, he marks that position on his chart, and joins the 

 point by a straight line with the place of his port as mai-ked 

 on the chart. This line shows him at once what course to 



