SEA ROUTES, CALM BELTS, AND VARIABLE WINDS. 331 



This is the superincumbent weight or pressure which is urging 

 the south-east trade-winds forward faster than the north-east. It 

 is inconceivably great; and to bring it witliin comprehensible 

 terms, the mariner will be astonished to hear that the weight 

 of atmosphere which is bearing dovm upon the deck of a first- 

 class clipper ship is 15 or 20 tons greater when he is sailing in 

 her through the south-east than it is when he is saihng in her 

 thi^ou2fh the north-east trade-winds. 



the prevailing 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. For this purpose he tabulated the results for the whole year of 17,810 

 observations — 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 tlie 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 

 yoiu- fleet, a regular series of experiments in the south-east trades upon speed, when 

 sailing at various angles with the course of the wind. Besides answering our 

 immediate 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 liave felt me so, pray 

 ascribe it to my desire to get by actual experiment an expression in tlie average- 

 speed of shii^s for the actual force and velocity of the Avinds. 



" 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. Mauky. 



" Admiral C. de Chabavnes, Commander-in-chief of the French 

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



Extract from a letter in reply to the foregoing : — 



" Montevideo, January 2i, 1860. 



" My dear Sir, — * * * * ^g y^^^ j-j^yg 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 sufficiently multiplied. I can, however, give as a result that the increase of 

 headway given by wind abeam over the headway with wind aft has been a httle 

 less than two knots ; when the velocity with wind aft was from 6 to 8 knots, the 

 force of the wind aft might be expressed by 4, and of the wind abeam by 6. * * * 



" C. DE Chabannes." 



London, November 26, 1860. 

 Just in time for insertion here, I receive from the gallant admiral the subjoined 

 veiy valuable and interesting series of experiments on the speed of his sliip : — 

 first, before the wind, ?. e. sixteen points, and so on for every two points to six, 

 and close hauled. At eiglit points the wind is abeam and at riglit angles with the 

 course of the ship ; at ten it is two points abaft the beam. From tliese experi- 

 ments we infer that an average sailer that goes six knots before the wind, will, if 



