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EFFECTS OF THE GULF STREAM.
"When I was mate* of His Majesty's ship Leopard, I was placed in charge of the identical ship which carried Jerome Buonaparte and his family to Europe, and selected for that purpose from being considered the fastest sailer out of Baltimore. I certainly never saw so perfect a model of a merchant vessel, or one more commodiously fitted up. I was, of course, prodigiously proud of my new and beautiful command; but had soon more important matters to attend to in the navigation of the ship, the difficulties of which may be easily explained.
"When we parted company from the Leopard, we were within a few days' sail of the coast of America, and may then have been a hundred leagues or so to the north-westward of Bermuda; consequently, still within the influence of the Gulf Stream, already alluded to as sweeping, in a north-eastern direction, along the shores of the United States. I was ordered to take my pretty charge to Bermuda, and proceeded to the southward accordingly. Foul winds, however, detained us for several days in the Gulf Stream, for the set of which current such an ample allowance was made, that when we reached the latitude of Bermuda, 32 N., it seemed almost certain that we were some thirty or forty miles to the westward of the island, that is, between it and the coast of America.
"From the land of Bermuda being low, it is not easily got sight of; and the whole cluster of islands being of small extent, they are often missed by navigators steering, as they conceive, directly for them. To those, indeed, who are provided with time keepers, there is no danger in following this direct method; for these instruments are now so admirably constructed, that an error in longitude which would carry a navigator past Bermuda, without seeing it, is, now-adays, very unlikely to occur. Ships, however, which have not the advantage of a chronometer, and consequently may not be sure of their longitude, generally find it prudent to run into the latitude of the island, and then steer along that parallel till they come in sight of their object. Most people are probably aware, that the latitude is an element in navigation almost at all times very easily determined, at least with sufficient accuracy for the purpose now alluded to. The longitude, as every mortal must have heard, is, or rather was, the grand stumbling-block in a sailor's way; and it will readily be understood, of what essential importance it must be to a ship, when running along a parallel of latitude, in search of a mere speck on the ocean, like Bermuda, that there should be no mistake as to which side of the island she really is upon. For if, in point of fact, the ship shall happen to be on the eastern side of the island, but, owing to some error in the reckoning, her captain believes that she is on the western side, he will naturally steer east along the parallel of latitude, instead of west, as he ought, of course, to do; and thus he will go on increasing his distance from the island, instead of shortening it.
"This curious case was precisely mine. The Gulf Stream, as it eventually appeared, had carried us eighty or ninety miles farther to
* i. e. Senior Midshipman.
the eastward than I had made allowance for, although an ample daily set in that direction was given her.* The superficial velocity of this mighty current, it seems, is occasionally accelerated or retarded by the prevalence of hard gales. At all events, whatever might be the cause of this unusual increase in the rate of the stream, it carried me so far beyond my mark, that when I reached the parallel of 32 N., I supposed myself in longitude 65 W., that is, about forty miles on the western or American side of Bermuda. As the wind was blowing from the east, of course I struggled hard to beat up against it, from supposing that my port lay to windward. It was fortunate this breeze was not blowing from the west, as I shall proceed to show."-P. 89. "On the day I reached the latitude of Bermuda (32) N.), I fancied the ship must certainly be on the western side of the island; the sun, however, happened not to be in distance,† as it is called, and, of course, no lunars could then be observed. Having, therefore, still nothing to trust to but the dead reckoning,‡ we, of course, continued beating all the morning to the eastward, under the full persuasion that Bermuda was in the wind's eye, due east of us, instead of being, as it really was, due west, on our lee-beam.§
"As the night approached, the sky became beautifully clear, and shortly after sunset I got my sextant to work. Before the twilight was ended, and the horizon too faint to admit of the altitudes being taken with accuracy, I had observed four or five sets of lunars. No time was lost in working out, when, lo and behold! the longitude, instead of being 65 W., as I made it by dead reckoning, appeared to be little more than 64 W., or some ninety miles farther to the eastward; thus showing that, although, as we supposed, we were thirty miles from the land, it was on the opposite side of the island from that on which we had imagined ourselves to be!
"What was now to be done? For, although on board the flag ship, where the accuracy or inaccuracy of a midshipman's lunars did not matter a straw, I had indulged in the usual presumption of fancying myself rather an expert observer, I was now filled with doubt and anxiety. All the ordinary allowances for the set of the Gulf Stream had already been made, and it was hardly to be conceived that in a week or ten days there should have occurred an error of a degree and a half. It appeared far more likely that some gross mistake had been committed in the figures of the computation, or in my mode of observing the lunars, than that such a huge augmentation to the strength of the current should have occurred at this particular moment.
"The American captain, who, like most commanders of ships of that class sailing from the United States, was an admirable navigator, and a very shrewd, obliging, and gentlemanlike person, happened to be so ill that he could not possibly come on deck, to make observations to corroborate mine. But he was able, though in bed, to go
* i. e. In the daily reckoning.
† i. e. The moon was not of convenient age.
The calculation without astronomical observation, by a consideration of the wind and the ship's rate of motion.
§ That part of the ship farther from the wind.
over the computations, the result of which, in his hands, agreed so nearly with what I made it, that he, at least, had no doubts of their accuracy, and recommended me at once to put the helm up, and steer to the westward. I had not confidence enough, however, in my own handiwork, for a decision so material to the success of the voyage. In short, I could not force my unpractised imagination to conceive that an island, which I had so much reason to suppose lay due east of me, could possibly be hit upon by steering due west."-P. 94.
"So, to work I went again, with my observations for the longitude. After all the adjustments of the sextant had been carefully examined, a new gang of lunars was taken, some with the same, and some with other stars, but all of them with a degree of attention which, if measured by the depth of interest felt in the result, I am not sure I have ever bestowed upon any similar course of observation since. Half of the distances I gave over to my friend, the captain, to compute, while I set about calculating the rest. After a time we exchanged computations, without communicating each other's results, till all were finished, and then we laid them side by side. The agreement amongst the whole observations was so near to one another, and corresponded also so closely with those taken earlier in the evening, that I could no longer have a doubt as to what should be done. About midnight, with a throbbing heart, and a mind filled with the most painful anxiety, I bore up, and, as we had a fresh breeze, spanked along merrily to the west. It was necessary, of course, in running in such a perilous neighbourhood, to keep a very bright look out; for although Bermuda, on its eastern side, is pretty clear of coral reefs, and we were quite certain of our latitude, it was not the sort of place to approach incautiously. When the moon went down, therefore, we shortened sail, but continued still slipping along at the rate of four or five knots, till morning.
"When the eastern sky first began to give some faint promises of a dawn, I felt my anxiety mount to a pitch scarcely bearable, and I kept peering with the night-glass into the gloom which still hung over the horizon in the supposed direction of Bermuda, as if my eagerness to see what was hid beyond, could have brushed away the night any quicker. When, at last, the day broke, and the well-known cliffs of St. David's Head, topped with dark green cedars and lightertinted orange trees, stood pleasantly up ahead of us, at the distance of a league and a half, I could have shouted for joy."-P. 97.
"I was not a little amused by finding we had reached the island before our own ship,† and, a few days afterwards, I had the satisfaction of rowing on board to report myself, before she anchored. The compliments paid to our success were due, it must be owned, to the sextant so opportunely sent to me; for, unless the dead reckoning had been checked by lunar observations, we might have been kept at sea a month; and, as the ship was short of provisions, serious consequences must have ensued."-P. 100.
* i. e., altered, and in this case reversed, the ship's course,
ti. e., "The Leopard."
RELATING TO THE EARTH'S SURFACE AND TO ITS DIURNAL
To find the Distance between two Places.
Repeat the following definitions :-*
Circle (F, p. 1); Centre (G, p. 1); Angle and Degree (L, p. 2); Globe or Sphere (B, p. 8); Great Circle and Small Circle (D, p. 8); Terrestrial Globe (def. 8); Equator (def. 13); Brazen Meridian (def. 20); Quadrant of Altitude (def. 48).
RULE. If the two places be on the Equator, count the degrees between them on that line; if, when one of the places is brought to coincide with the graduated surface of the Brazen Meridian, the other be likewise cut by it, count the degrees of distance between them as shewn by that graduation. If otherwise, lay the O of the Quadrant of Altitude upon one of the places, and that portion of its graduated edge which will coincide with the other place will give the degrees of distance. The English miles of distance may be found by multiplying the degrees so found by 69; or nearly, and more readily, by multiplying them by 70.
* The appropriate definitions, &c., are given before the rule of each problem. It is desirable that they should be committed to memory; but, in any case, they should be duly considered before working the questions of the problem.
DISTANCES BETWEEN PLACES.
1. Find the distance in degrees of a great circle between Quito and Chatham Island, (Easternmost of the Galapagos)?
2. Between Quito and the island of Saint Thomas, Gulf of Guinea)?
3. Between the mouth of the Fish River, or Angra Pequena, (S. W. coast of Africa) and Lake Tchad, (of Bornou, its interior)?
4. Between Land's End and St. Helena ?
5. Between Philadelphia and Carthagena, (N. of South America)?
6. Between Madrid and the Orkneys?
Cape Chidley, (Labrador)
8. Suppose a line to descend to the Earth's centre from Port Royal, Jamaica, and another line to descend to meet it, at the Earth's centre, from the Island of Bermuda; what number of degrees would measure the angle made by these two straight lines?
9. Suppose a ship in Port Royal, Jamaica, and another at the Island of Bermuda; how far distant, in degrees of a great circle, must the two Stars be to which these two ships are pointing their masts, at any given instant?
10. How many degrees in the heavens would the mast of a ship describe by its pointing, if it could steadily sail by a straight course from the south coast of Owhyhee to Otaheite, (Tahiti)?
11. What is the breadth (in English miles) of Africa, from Cape Verd to Cape Guardafui ?
12. What difference is there in English miles between this width of Africa, and the shortest distance between London and Jamaica ?
13. If a star be over my head, at any given instant, at Blackheath, how many degrees in the heavens is that star separate from it, which is then overhead to my friend at Alexandria?