August 31, 1905] 



NA TURE 



447 



The compilers of such a map have a difficult task. Dis- 

 crepancies are, of course, multitudinous. Nothing agrees, 

 and one has to accept, reject, and adjust as best he can 

 on his own responsibility and with what knowledge he 

 can procure of the respective trustworthiness of each author. 



Happy is he if he has even a few positions in his map 

 which have been properly determined, as between them he 

 is saved from the constantly increasing errors of adding 

 one little area to another, which if carried on indefinitely 

 culminates in great errors. 



Of course such maps are of no practical use, save as 

 giving a very general idea of a country, and when required 

 by the administrator or traveller lead to endless mistakes 

 and annoyances. 



The feature of our globe which is now, broadly speak- 

 ing, most accurately laid down is the coast-line. The safety 

 of navigation has caused general marine surveys to be 

 carried on all over the world during the nineteenth century, 

 which have finally determined the position and shape of 

 the boundaries of the sea. 



These surveys, executed for the most part by skilled 

 naval officers with proper instrumental outfit, and supplied 

 especially with trustworthy chronometers, and based upon 

 frequent carefully determined astronomical positions, have 

 resulted in this boundary line being delineated with an 

 accuracy, so tar as its absolute position is concerned, far 

 in advance of any other main feature in maps. 



Here I may perhaps explain to those unversed in these 

 matters why this is so. 



The position of any spot on the earth's surface can be 

 ascertained in two ways ; either by careful measurement 

 by means of an accurate system of triangles from another 

 spot already fixed, or by independent observations of the 

 heavenly bodies and calculations from them, which give 

 the precise latitude and longitude of the place. The former 

 is suitable for positions Inland, but entails much time and 

 labour, and is only adopted when a perfect map is to be 

 made, for which it Is the indispensable foundation. The 

 latter can be carried on from a ship, and in most 

 circumstances only from a ship, because of the limitations 

 of the methods of determinating longitudes. 



Longitude can now be satisfactorily and rapidly ascer- 

 tained in two ways : by the electric telegraph or by use of 

 chronometers. 



Th" places served by the electric telegraph are still few, 

 and its use is therefore restricted ; but the chronometer has 

 been in working use for more than a hundred vears. 



This instrument, which is merely a watch of especial 

 construction, will only keep a steady rate when it is un- 

 disturbed by irregular shocks or motions 



No means have yet been found for transporting a chrono- 

 meter on land without upsetting Its regularity, and there- 

 fore rendering it useless ; but on board a ship it can be 

 so suspended and stowed as to prevent its being disturbed 

 by any ordinary movements of or in the ship. The ac- 

 curate time of any place departed from, ascertained by 

 astronomical observations, can therefore be carried about 

 on board ship for considerable periods, and by comparison 

 with the local time, also determined by sextant observa- 

 tions of the heavenly bodies, at any required spot on the 

 coast, the difference of longitude is at once obtained with 

 very small limits of error when a number of chronometers 

 are employed. These two simple yet marvellous instru- 

 ments, the sextant and the chronometer, have thus placed 

 in the hands of sailors ready means of fixing with great 

 exactitude and celerity the position of selected points on 

 coasts all over the world ; and it will be seen that, while 

 the detail of the line of coast between such fixed positions 

 will depend upon the degree of accuracy of the survey or 

 sketch, the general line cannot get far out, as it is con- 

 stantly checked at the selected points. 



It is not claiming too much to say that at the present 

 time very few salient points on the coast-lines of the 

 world are as much as two miles in doubt. 



It should be a source of great satisfaction to the Briton 

 to know that both these Instruments were devised by 

 Englishmen, John Hadley producing the sextant in 1730, 

 in the form still used, on the basis of Ideas formulated 

 by Newton fifty years before; and John Harrison the 

 chronometer in 1736. The latter instrument has undergone 

 modifications in detail, but the principle remains the same. 



It required seventy years before its value was fully recog- 

 nised and it came into general use. 



It is a still further satisfaction to think that it is British 

 naval officers who have made by far the greatest use of 

 them in mapping the coasts of the whole world. Since 

 the time of the great Captain Cook British surveying 

 vessels have been constantly employed in this work, not 

 only In British colonies, but In all parts, aiding and often 

 paving the way for British commerce, and for the men-of- 

 war that protect it. 



It Is difficult to find coasts of any extent that have not 

 been laid down by British marine surveyors. The whole of 

 Africa has been their work. By far the greater part of 

 America, all the south and east coasts of Asia, Australia, 

 and most of the innumerable islands in all oceans have 

 been fixed and laid down by them. Even in the Medi- 

 terranean, until very lately, the charts were mostly founded 

 on British surveys, and the improvements now being 

 carried out by other nations on their own coasts In details 

 required for modern navigation do not materially modifv 

 the main shapes and positions formerly determined by the 

 British. 



It has been, and is, a great work, and I hope I may 

 be pardoned for dwelling on it with pride as the result 

 of the wise administration of the Admiralty for many years, 

 and of the immediate labours of my predecessors as Hydro- 

 grapher, and as a very great contribution to geographical 

 knowledge, more especially as I do not think that it is 

 generally realised that this great advance in geographic 

 accuracy Is due to marine surveyors. 



To give an idea of the comparative accuracy of the 

 chronometer method, I may mention that on taking at 

 hazard eleven places distributed all over the world at great 

 distances from England, the longitudes of which have been 

 recently determined by means of the electric telegraph and 

 elaborate series of observations, I find that the average 

 difference between the chronometer and the telegraph posi- 

 tions is 700 yards. The shapes of the different continents 

 and the positions of islands as at present on our maps and 

 charts will never be altered except in insignificant degree, 

 and the framework is ready for many years' work of land 

 mapping. 



It is not to be inferred from what I say that marine 

 surveys are approaching their close. It is far otherwise. 

 The time given to these enormous extents of coasts and 

 seas, and the necessarily small scales on which the surveys 

 have been carried on, have caused them to be very im- 

 perfect in all details. Hundreds of rocks and shoals, both 

 stretching from the land and isolated in the sea, have been 

 missed in the course of them, and loss of ships and life on 

 these unknown dangers still continues. With the increase 

 of shipping, increased number of ships of heavy draught, 

 the closeness of navigation due to steam, and the desire 

 to make quick passages, smaller inaccuracies of the charts 

 become yearly of greater importance. 



As an Illustration of the condition of affairs I may 

 mention that In Hamoaze, the Inner harbour of Plymouth, 

 one of the headquarters of the British fleet for more than 

 300 years, a small but dangerous pinnacle of rock was only 

 discovered five years ago ; whilst numerous other dangers 

 of a similar character have been yearly revealed in close 

 surveys of other harbours In the United Kingdom, supposed 

 to be well examined and charted in the last century. 



There never was a greater need for close marine surveys 

 of places frequented by ships than now. 



It is interesting to look back and see the gradual progress 

 of the delineation of the world and to mark how very 

 recent any approach to accuracy is. 



The very earliest maps of any extent of country are un- 

 fortunately lost to us. The first man who made a map of 

 which any historical record exists is Anaximander of Miletus, 

 about 600 B.C., but we know nothing of it. A map is 

 mentioned by Herodotus as having been taken in 500 B.C. 

 by .^rlstagoras of Miletus in the shape of an engraved 

 bronze plate whereon the whole circuit of the earth was 

 engraved, with all its seas and rivers, to influence Cleo- 

 menes. King of Sparta, to aid the lonians against Persia. 

 This was probably the work of Hecatseus, to whom early 

 Geography owed much. His works are also only known 

 to us by quotation ; but they are especially Interesting as 

 containing an early idea of the limits of Africa, which ho 



NO. 1870, VOL. 72] 



