During our course from Teneriffe to Bona Vista we saw great numbers of flying fish, which from the cabin windows appear beautiful beyond imagination, their sides having the colour and brightness of burnished silver; when they are seen from the deck they do not appear to so much advantage, because their backs are of a dark colour. We also took a shark, which proved to be the Squalus Carcharias of Linnæus.
Having lost the trade wind on the 3d, in latitude 12° 14ʹ, and longitude 22° 10ʹ, the wind became somewhat variable, and we had light airs and calms by turns.
On the 7th, Mr. Banks went out in the boat and took what the seamen call a Portuguese man of war; it is the Holuthuria Physalis of Linnæus, and a species of the Mollusca. It consisted of a small bladder about seven inches long, very much resembling the air-bladder of fishes, from the bottom of which descended a number of strings, of a bright blue and red, some of them three or four feet in length, which, upon being touched, sting like a nettle, but with much more force. On the top of the bladder is a membrane which is used as a sail, and turned so as to receive the wind which way soever it blows: this membrane is marked in fine pink-coloured veins, and the animal is in every respect an object exquisitely curious and beautiful.
We also took several of the shell-fishes, or testaceous animals, which are always found floating upon the water, particularly the Helix Janthina and Violacea; they are about the size of a snail, and are supported upon the surface of the water by a small cluster of bubbles, which are filled with air, and consist of a tenacious slimy substance that will not easily part with its contents; the animal is oviparous, and these bubbles serve also as a nidus for its eggs. It is probable that it never goes down to the bottom, nor willingly approaches any shore; for the shell is exceedingly brittle, and that of few fresh water snails is so thin: every shell contains about a teaspoonful of liquor, which it easily discharges upon being touched, and which is of the most beautiful red purple that can be conceived. It dies linen cloth, and it may perhaps be worth enquiry, as the shell is certainly found in the Mediterranean, whether it be not the Purpura of the ancients.
On the 8th, in latitude 8° 25ʹ North, longitude 22° 4ʹ West, we found a current setting to the southward, which the next day in latitude 7° 58ʹ, longitude 22° 13ʹ, shifted to the N. N. W. ¾ W., at the rate of one mile and a furlong an hour. The variation here, by the mean of several azimuths, appeared to be 8° 39ʹ W.
On the 10th, Mr. Banks shot the black-toed gull, not yet described according to Linnæus’s system; he gave it the name of Larus crepidatus: it is remarkable that the dung of this bird is of a lively red, somewhat like that of the liquor procured from the shells, only not so full; its principal food therefore is probably the Helix just mentioned. A current to the N. W. prevailed more or less till Monday the 24th, when we were in latitude 1° 7ʹ N., and longitude 28° 50ʹ.
On the 25th we crossed the line with the usual ceremonies, in longitude 29° 30ʹ, when, by the result of several very good azimuths, the variation was 2° 24ʹ.
On the 28th, at noon, being in the latitude of Ferdinand Noronha, and, by the mean of several observations by Mr. Green and myself in longitude 32° 5ʹ 16ʺ W., which is to the westward of it by some charts, and to the eastward by others, we expected to see the island, or some of the shoals that are laid down in the charts between it and the main, but we saw neither one nor the other.
In the evening of the 29th, we observed that luminous appearance of the sea which has been so often mentioned by navigators, and of which such various causes have been assigned; some supposing it to be occasioned by fish, which agitated the water by darting at their prey, some by the putrefaction of fish and other marine animals, some by electricity, and others referring it into a great variety of different causes. It appeared to emit flashes of light exactly resembling those of lightning, only not so considerable; but they were so frequent, that sometimes eight or ten were visible almost at the same moment. We were of opinion that they proceeded from some luminous animal, and upon throwing out the casting net our opinion was confirmed: it brought up a species of the Medusa, which, when it came on board, had the appearance of metal violently heated, and emitted a white light: with these animals were taken some very small crabs, of three different species, each of which gave as much light as a glow-worm, though the creature was not so large by nine-tenths: upon examination of these animals Mr. Banks had the satisfaction to find that they were all entirely new.
On Wednesday, the 2d of November, about noon, being in the latitude of 10° 38ʹ S., and longitude 32° 13ʹ 43ʺ W., we passed the line in which the needle at this time would have pointed due north and south, without any variation: for in the morning, having decreased gradually in its deviation for some days, it was no more than 18ʹ W., and in the afternoon it was 34ʹ East.