The Lieutenant and Commander

tain their hold on the public mind. In some cases it would almost seem that the pleasure which springs from genuine philosophical inquiry is subordinate to that which arises from

ectly connected with the sea, the existence of error may often be injurious: and, although it is not very easy t

eristics may eas

rts of the Pacific and Atlantic oceans that the true Trade-winds blow. In the Indian and China seas, and in many other portions of the great tropical belt, periodical winds, called Monsoons, are found. These shifting Trades exact the closest study from the practical navigator, in consequence of their extensive variety and seeming complication. But they are not less deserving the attention of merely curious inquirers, from the

And I have even seen sailors (old sailors too) quite surprised, and rather provoked, when they have encountered very different winds in those parts of their voyage, where, being misled by the force of names alone, they had taught themselves to expect a regular breeze from a particular quarter. But, in point of fact, the Trade-winds do very seldom blow directly from north-east and south-east; neither are they uniform in their direction on the same spot at different seasons of the year, nor is their strength unifor

rtain it is, that no sailor who ever crossed the equinoctial line could possibly have furnished him with two of his principal statements. The Trades are not stron

expand, or become specifically lighter, and would consequently rise. The adjacent air, both on the north and south, being cooler, and, of course, heavier, would rush in to supply the place of the heated air. This air coming from the regions beyond the tropics would, in its turn, be heated, and rise on reaching the warmer equatorial regions, giving place to a fresh supply, which, it is easy to see, must be furnished by the descent of that portion of air formerly heated at the eq

ollow the opposite directions, and stream towards the poles. But the instant we conceive the earth put into rotatory motion from west to east, a change would take place in the course of these a?rial currents, both above and below. It must be recollected that a volume of air, when once put in motion, wil

and being surrounded by an atmosphere, were then made to revolve on its axis, it would carry the atmosphere round with it exactly at the rate at which it was itself goi

moves only 860, or 140 miles slower. The average whirling velocity of the earth's easterly motion, in the space between the eq

hatever might be the rotatory motion impressed upon the earth. If, however, we next suppose, what really is the case, that the air over the tropical region is more heated than that wh

e apparent motion of the air from the east, caused by the relative difference of the rotatory velocity between the air and earth, is great, compared to the other motion of the air, caused by its being draw

, the wind, as it approaches the equator, will appear to blow less and less directly from the eastward. But, while the earth's rotation within the tropics is thus acting on the slower-moving air which has travelled to it from beyond the tropics, with increased friction at every successive moment, there has been no such powerful counteracting influence in operation to diminish the meridional motion impressed on the air in question; for, although in proceeding from the tropics towards the equator, the wind might, at first sight, be supposed to have its speed somewhat lesse

tion to the east of the temperate zone, it will follow, that, if this difference of velocities between the earth and the air in contact with it be diminished or annihilated, the easterly character of these winds will be diminished or annihi

the eastward, but it soon comes over parts of the earth moving more than 100 miles per hour faster to the eastward than itself. The difference of velocity in the earth's rotation

y-increasing friction of the earth's rotation to act upon it, and draw it more and more entirely to the east. By the time it has reached the equatorial regions, the friction of the earth's surface h

uatorial limits, blowing, not from the east, as Hadley, Dr. Young, and others, conceived, but directly from the north and from the south respectively. The strength and velocity of the Trades at these places is, in general, considerably diminished, chiefly, perh

served to proceed in the contrary direction to the winds below. On the top of the Peak of Teneriffe I f

e, will now, I imagine, be readily understood. Before setting out, however, I must strongly recommend any one wishing to see these matters clearly, to have th

oring, or communicating with the shore. The captains by such ships are pretty deeply, if not very loudly, abused by all hands, passengers especially, who are perhaps the most dissatisfied, because the most idle, of mortals. Shortly after leaving Madeira, which is in 32-1/2° north latitude, a ship may expect to meet the Trades; but she cannot calculate with any certainty upon catching them till she arrives at the parallel of 28°. On first reaching the Trade-wind it will be found to

November it is shifted back as far, sometimes, as 13° north, but it seldom extends as far south as 8° north. Subjects which are treated of in a series of tables showing the equatorial limits of both Trade-winds, deduced by the late Captain James Horsburgh, hydrographer of the East India Company, from the observations

tward, from a cause afterwards to be explained, it is obvious enough why this part of the homeward voyage is always more easily made than the outward passage. These southerly breezes, which are met with in the Variables, blow at times with considerable force, and greatly perplex the young nav

n December or January. I now speak more particularly of what happens in the Atlantic. In the wide Pacific, far from land, fewer modifying circumstances

irectly in the outward-bound navigator's teeth. He must have patience, however, and strive to make the most of it by keeping on that tack by which most southing is to be gained. It is now, I believe, generally held to be the best practice to place the ship between 18° and 23° of west longitude on losing the north-east Trade; and likewise to endeavour, if possible, to cross the e

be too solicitous about making southing, and hugs the wind much too close; whereas he ought rather to keep his ship off a little, give her a fathom or two of the fore and main sheets, and take a small pull of the weather topsail and top-gallant braces, to ensure making good way through the water. Indeed, many officers go so far as to recommend flanking across the south-east Trade with a fore-topmast studding-sail set. Although, I think, there can be no doubt of the soundness of this advice, I confess that it does require no inconsiderable degree of faith to adopt a course, which, apparently, takes the ship not directly away from her object, but very much out of the straight road. In this resp

e southern hemisphere, and far from the land, the wind may be said to blow from the westward almost as steadily as the Trades do from the eastward. The great object, there

t is shown that the average length of the voyage from Liverpool to America, that is, towards the west, was forty days; while the average length of the homeward passage, or that from west to east, was only twenty-three

rty degrees of latitude along the upper regions of the atmosphere towards the poles it becomes cooled, and is ready to descend again, between the latitudes of 30° and 60°, to supply the place of the lower air, drawn off towards the equator by the Trade-winds. But this partially-cooled air falls on a part of the earth's surface which is moving much more slowly towards the east, in its diurnal rotation, than the air which has descended upon it, and which is still impressed with a great proportion of its eastern velocity

, between the Bay of Panama and the Peninsula of California, from latitude 8° to 22° north. If the huge continent of Mexico were taken away, and only sea left in its place, there can be no doubt but the ordinary phenomena of the Trade-winds would be observable in that part of the Pacific above mentioned. Cool air would then be drawn from the slow moving parallels lying to the northward, towards the swift moving latitudes, near the equator, in order to supply the place of the rarefied air removed to the higher regions of the atmosphere, and, of course, north-easterly breezes would be produced. But when the sun comes over Mexi

the relative difference in these two motions. At that particular season of the year when the sun is in high southern declination, Mexico is not exposed to his perpendicular rays. The equatorial

der of Africa, become as vehemently heated, or more so, perhaps, than Mexico, and this draws the air from the equat

upon which their extensive utility in a great measure depends, amongst nations where the complicated science of navigation is but in a rude state. Myriads of vessels sail from their homes during one monsoon before the wind, or so nearly before it, that there is no great skill required in reaching all the ports at which they wish to touch; and when the wind shifts to the opposite quarter, they steer back again, in like manner, wi

scrape, into which the lubberly Chinese junks sometimes fall. They might, and certainly would, lose time in making a roundabout of some two or three hun

rotation a greater degree of velocity in the direction from west to east than belongs to the countries and seas just mentioned; and this additional velocity, combined with its motion from the equator, in rushing to fill up the vacuum caused by the rarefaction of the air over those regions intersected by the tropic, causes the south-west monsoon. "This wind," sa

he same space that the south-west monsoon prevails in the opposite season mentioned above. But the monsoons are subject to great obstructions by land; and in contract

China), lying under the northern tropic, become comparatively cool. The air over these regions becomes relatively more dense than the rarefied air near the line; consequently the cool air rushes to the southward to interchange places with that which has been heated; and as the cool air c

ions in different places, all of which are so readily explained by the foregoing theory, that they form

lland; and it is generally confined between the equator and 10° or 11° south latitude, but subject to irregularities." This westerly wind is evidently produced by the air drawn actually from the equator towards the slower moving latitudes of the earth, by the rarefaction of the air to the southward when the sun is near the

New Guinea;" for it will be obvious to any one who inspects the globe, on reading this passage, that there occurs in the neighbourhood of the spots alluded to a powerful cause for the strength and regularity of the monsoons. The enormous island, or continent, as it might almost be called, of Australia, may well be supposed to act the part of a heater from Oc

climates, and Horsburgh's East India Directory, which I have quoted above so frequently, is by far the best authority with which I am acquainted on these subjects. At the same time, I must not omit to do justice to a beautifully-written and accurate Essay on Winds and Currents, by that Princ

TNO

e secretary to the American navy, in the true analytical spirit, and immense progress made in our knowledge of these winds

For every degree the ship changes her longitude south of the Line she sails a shorter distance along the great circle than on any other curve; for