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in longitude of two places is considerable, great circle sailing fails to 

 save much distance ; and, on the other hand, when the difference of 

 longitude is very great, this sailing cannot he adopted, and thus the 

 sailing withholds its chief advantage in practice when its value in 

 theory is greatest. Thus, in an Australian voyage, we should savfi 

 more distance than in any other ; but from the nature of great circle 

 sailing, it is for that purpose impracticable, since it would lead the ship 

 directly across the south pole. 



This I found to be the most formidable obstacle seven yeare ago, 

 when I attempted to devise means of bringing great circle sailing into 

 general use. For the purpose of removing this difficulty, I endeavoured 

 to solve this problem : — If it be undesirable for the mariner to approach 

 the pole nearer than any given latitude, how can he sail by the shortest 

 route without violating this restriction? This problem I solved by the 

 invention of a new sailing, which I call "composite saihug." 



To explain its nature, and demonstrate the fact of its being a com- 

 plete solution of this problem, we will have recourse again to the 

 principle of the carpenter's chalk line. This line we have found to-give 

 us the shortest track, subject to restrictions. It gives us, absolutely, 

 the shortest track over a plane ; but on the surface of a globe, restricted 

 by the rotundity of the surface, it describes the arc of a great circle, 

 that being the shortest track over such a surface. In composite sailing 

 we have a second restriction, not altogether a physical one, but rather 

 a prudential one — we ought not to go nearer the pole than a given 

 latitude. Let us, in the artificial globe, substitute a physical restric- 

 tion for the real prudential one, by having the parallel raised above the 

 surface. Now the string, when subject to tension, describes that which 

 we call the "composite track." It is the sailing made by Australian 

 ships that have made rapid passages, and is frequently denominated 

 great circle sailing. 



I have been charged with something like pi'esumption in lajing 

 claim to the honour of being the inventor of a sailing. During 

 the past summer, this matter was the subject of a correspondence 

 with Lieutenant Mauiy. I may perhaps be allowed first to 

 obsei*ve that ray remarks, which induced this correspondence, were 

 made in consequence of having read this paragraph in a Liverpool 

 newspaper, headed " Lieutenant Maury's Great Circle Route to 

 Australia," which is nothing more than a description of a voyage 

 similar to those already accomplished by Boyce, Forbes, and others ; 

 and I now feel thankful to Mi: Rankin for having given me the oppor- 

 tunity to establish for Godfrey, Boyce, Forbes, and others, the honour 



