47 8 



NA TURE 



[October 7, 1922 



Letters to the Editor. 



[The Editor does not hold himself responsible for 

 opinions expressed by /lis correspondents. Neither 

 can he undertake to return, or to correspond with 

 iters of, rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.} 



Dampier's "Discourse of the Winds" and the Dis- 

 tribution of Wind on the Earth's Surface- 



Dampier's " Voyages " are well known, at any rate 

 by name, but his " Discourse of the Winds " is seldom 

 referred to. It is, however, well worth careful 

 examination and, so far as I can judge, contains as 



rule are not of the type who place their knowledge 

 on record. With the " Discourse " Dampier publishes 

 maps of the hemispheres in which his observations are 

 summarised. 



For his purposes he divides the earth's surface into 

 four regions, namely, the two trade wind areas and 

 those to the north and south of them. These latter he 

 calls the " Regions of Variable Winds." The direc- 

 tions of the trades are indicated in the maps by lines 

 and arrows, but naturally and rightly the regions of 

 variable winds are left blank. 



No indication is given of the directions of the wind 

 on land, but what he calls coastal winds, that is winds 

 the direction of which is influenced by the proximity 

 of land, are shown in some detail. 



Parts of the maps are here reproduced (on the 



Fig. I. — Reproduction of parts of Dampier's Maps to show coastal winds in the Trade wind 



much information about the distribution of winds as 

 any of the modern works on the same subject. 



In this " Discourse " Dampier propounds no 

 theories, but aims at setting down the general char- 

 acter of the winds encountered by ships in all parts 

 of the world, using for this purpose his own observa- 

 tions, and such other information as he has gathered 

 from sources which he considers trustworthy. 



It must be remembered that in Dampier's time 

 (late seventeenth and early eighteenth centuries), the 

 ships employed even for the longest voyages were 

 small, and the direction and strength of the prevailing 

 winds were much more important to navigators than 

 they are at the present time. It is true that there are 

 stili plenty of small sailing craft in various parts of 

 the world, the captains of which are probably well 

 acquainted with local conditions, but these men as a 



NO. 2762, VOL. I IO] 



original scale) which show that "coastal" influence 

 in the trade wind areas extends farther to the west 

 (i.e. to leeward) of the continents than to the east. 



Although it is impossible to determine a priori 

 what the true wind should be at any given spot, it is 

 not without interest to consider what would happen 

 in certain imaginable conditions much simpler than 

 those actually existing, and to see whether in such 

 conditions the air currents, etc., would at all resemble 

 those which are observed. 



Starting with the earth as the only body in the 

 universe, without rotation, and at a temperature of 

 absolute zero, let its surface be uniform and level, and 

 let its volume and that of adjacent space be divided 

 into elementary conical cells proceeding from the 

 earth's centre. Let the walls of the cells be non- 

 conductors of heat but transparent to radiation. 



