34-i THE PHYSICAL GEOGRAPHY OF THE SEA. 



643. With these barometric observations, and the assumed fact 



"That the atmospherical circulation is more active in the southern than in the 

 northern hemisphere appears to be indicated also by the " brave west winds" of the 

 extra-tropical south. ^ If the air performs its circuit more rapidly through one system 

 of trade-winds than the other, then it follows that it must perform its circuit more 

 rapidly also along those regions through which it has to pass in order to reach such 

 rapid trades. Consequently, there should be a great difference between the gales 

 of the northern and those of the southern hemisphere. If we suppose the general 

 circulation of the northern hemisphere to be sluggish, the air in its circuits there 

 would have time to tarry by the way, as it were, and to blow gales of wind from all 

 points of the compass. On the contrary, if the general circulation of the southern 

 hemisphere be brisk and active, the air in its general circuits, like a fast train on the 

 railway, would not have so much time to tarry by the way, because, like the cars, it 

 must he up to time. Hence, admitting this view of the matter to be correct (and you 

 perceive that for the want of the experiments already alluded to we are groping in 

 the darkness of conjecture), though we might expect gales of wind in the extra- 

 tropical regions of the south, yet they would, for the most part, blow with the pre- 

 vailing direction of the wind, and not against it. Thus the gales on the polar side 

 of Capricorn should, particularly at sea, have westing in them always — almost. 



" In corroboration of this view, I may mention, on the authority of a paper just 

 received from Lieutenant Van Gogh, of the Dutch Navy, that the gales of wind 

 which take place between the meridians of 14° and 32° E., and between the paral- 

 lels of 33° and 37° south, have been discussed at the Meteorological Institute of 

 Utrecht. Eor this purpose he tabulated the results for the whole year of 17,810 ob- 

 servations — an observation comprehending a period of eight hours. According to 

 these observations, it is blowing a gale of wind off the Cape of Good Hope 7.16 per 

 cent, of the whole year, and from the following quarters : namely, between N.N.W. 

 and S.S.W. 6.43 per cent. ; from all other quarters, 0.73 per cent. 



"Perhaps you may find it convenient to institute, with some of the vessels of your 

 fleet, a regular series of experiments in the southeast trades upon speed, when sail- 

 ing at various angles with the course of the wind. Besides answering our immedi- 

 ate purpose, the results might enable us to convert ships into very good anemometers 

 for all winds except gales. 



" Pardon me for being so tedious upon this subject. If you have felt me so, pray 

 ascribe it to my desire to get by actual experiment an expression in the average speed 

 of ships for the actual force and velocity of the winds. 



"Wishing you all success and good luck in the investigation which you have in 

 hand, pray believe me, my dear admiral, yours very truly, M. F. Maury. 



^'Admiral C. de Ciiabanneb, Commander-in-chief of the French) 

 Naval Division of Brazil and La Plata, Rio de Janeiro." / 



Extract of a letter in reply to the foregoing : 



'•'• Montevideo, January 25, 1S60. 



" My dear Sir, — * * * * ^g y^^ have indicated to me in your letter of 

 April, I have caused to be made, by a brig of my division, experiments upon the 

 comparative velocities wind abaft and wind abeam with a given force of wind, but I 

 have not yet been able to deduce any positive rule, the experiments not having been 

 •ufficiently multiplied. I can, however, give as a result that the increase of head- 



1 See also Plate XIII., and § G33 and § 6C3. 



