TRANSACTIONS OF THE SECTIONS. 35 
each one, the combined experience of all who have sailed before him over the same 
part of the ocean. $ 
To illustrate the importance of this undertaking, I may be excused for alluding to 
some of the practical results already obtained. ¢ 
In consequence of the better knowledge afforded by this chart with regard to the 
winds in the North Atlantic Ocean, the average passage from the ports of the United 
States to the Equator (and consequently to all ports the way to which leads across 
the Equator) has been shortened several days. I have the tracks of four vessels 
which have been to Rio de Janeiro in Brazil, by the new route proposed on this 
chart. They have invariably made shorter passages than vessels sailing at the same 
time by the old route. The average passage by the old route to the line, is forty-oue 
days ; the mean of the four which have tried the new route is thirty-one days, the 
ee being twenty-four days, the quickest of the season, and the longest thirty- 
nine days, 
The i RO already collected has enabled me to strike out numerous vigias 
and fabulous dangers which deface our best general charts of the ocean, and which 
greatly increase the sources of anxiety which at all times surround the navigator. 
The positions of these vigias are laid down on the chart as doubtful, and when the 
_ ship is in the vicinity of any of them, it is a sleepless time with her master. I have 
the tracks of several hundred vessels which pass over and within 5° of some of these 
vigias, so that, if they were in existence, they certainly would have been seen by one 
or more. But they are not mentioned in the log, and it may therefore be fairly con- 
cluded that they do not exist. At the proper time I shall publish a list of vigias 
which these charts show ought to be erased. AS Altay 
The grouping together such a mass of facts in the manner proposed, will lead to 
many collateral, highly interesting and valuable results. Take as an example what is 
shown on the charts before you. If you will examine sheet No. 3, you will see that 
the trade-winds between the parallels of 5° and 10° N. from the coast of Africa 
nearly to the middle of the Atlantic, lose their trade character and become the 
baffling, variable airs known to sailors as the doldrums, whereas between the same 
parallels (sheet No. 2) on the American side, they blow with great regularity from 
the northward and eastward. In the former case, the sun shining upon the plains and 
deserts of Africa rarefies the air to windward, and this calls upon the winds of the 
sea to return and restore the equilibrium. In the latter case, the sun shining upon 
_ the plains of South America heats the air to Jeeward, and causes the trade-winds to 
hasten on and restore the equilibrium. In the one case the rarefaction takes place 
to windward, in the other to leeward, and the effect produced is clearly indicated by 
the chart, and is precisely such as might be expected. 4s 
Again, examine the winds in the Gulf of Mexico, sheet No. 1. The prevailing 
winds here are from the southward and eastward, while between the same parallels 
(sheet No. 2) and upon the broad ocean, the prevailing winds are the N.E. trades. 
As soon as the effect is seen the cause becomes obvious. Is it not to be found in 
the action of the sun upon Texas and the States of Northern Mexico? There is an 
immense body of land in this direction, and the heat of the sun upon it causes the 
winds to set towards it from the Gulf of Mexico. What effect a day of rain or of 
clouds over this body of land has upon the winds off the Pacific coast of Tehuan- 
tepec and Central America, is one of the interesting results to be anticipated from 
the work before us. 
But perhaps the most interesting result yet obtained—and the undertaking is but 
just commenced—is the discovery within the limits of the N.E. trades in the At- 
lantic, of a region in which the prevailing winds are from the southward and west- 
ward. 
This region is limited in extent, and is somewhat in the shape of a wedge, with its 
base towards the coast of Africa between the Equator and 10° N, It extends from 
long. 10° W. to about 25° W., being bounded by the Equator for one side, and by a 
Tine drawn from lat. 10° N. long. 10° W. to lat. 5° N. long. 25° W. on the other. 
How the case may be to the south of the Equator, I am not prepared to say. But 
to the north of it, I have discussed 2292 independent observations made within the 
above-described region by different vessels on their voyages across it. Included 
among these observations, calms were encountered on 246 occasions, leaving 2046 
Dz 
