Texts Texts

Extracts from a Journal, written on the Coasts of Chili, Peru, and Mexico, in the years 1820, 1821, 1822.

Basil Hall, R.N., F.R.S.

CHAPTER XXXVIII.

Interesting navigation down the river of Guayquil by means of an operation called kedging—meeting with the American frigate constellation—visit to the galapagos islands—experiments made with captain kater's pendulum—terrapins or land tortoises.

The manner in which we proceeded down the river is so curious, and, as far as I know, so rare, that I shall attempt to make it intelligible even to readers who are not nautical.

In the navigation of rivers which have many windings and shallow places, the chief danger is, that the tide will force the ship either on the banks or on some shoal lying in the stream: there is a risk of this even when under all sail, and with a good breeze of wind; for the tide sometimes runs so rapidly and irregularly as to hustle her on shore, before the sails can be made to act. When the wind is blowing faintly, and, at the same time, not quite fair, the danger of this happening is much increased. On such occasions, instead of sailing in the usual manner, with the ship's head foremost, no sails whatever are set, and the stern, instead of the bow, is made to go first, an operation technically called Kedging.

If the anchor by which a vessel in a tide's-way be raised off the ground, she will, of course, immediately begin to drift along with the stream, and most probably soon run aground. The ship, it must be observed, when under these circumstances, and with no sail set, can make no progress through the water, but must drift along with it like a log; consequently the rudder will have no effect in directing her course, and she will be left entirely at the mercy of the tide. The operation of kedging is a device to produce a relative motion between the ship and the water, in order to bring the directing power of the rudder into action. This object is accomplished by allowing the anchor to trail along, instead of being lifted entirely off the ground, as in the first supposition. It is known practically, that the degree of firmness with which an anchor holds the ground depends, within certain limits, upon its remoteness from the ship. When the anchor lies on the ground immediately under the ship's bows, and the cable is vertical, it has little or no hold, but when there is much cable out, the anchor fixes itself in the bottom, and cannot without difficulty be dragged out of its place. In the operation of kedging, the cable is hove, or drawn in, till nearly in an upright position; this immediately loosens the hold of the anchor, which then begins to trail along the ground, by the action of the tide pressing against the ship. If the anchor ceases altogether to hold, the vessel will, or course, move entirely along with the tide, and the rudder will become useless. However, if the anchor be not quite lifted off the ground, but be merely allowed to drag along, it is evident that the ship, thus clogged, will accompany the tide reluctantly, and the stream will in part run past her; and thus a relative motion between the vessel and the water being produced, a steering power will be communicated to the rudder.

In our case, the tide was running three miles an hour; and had the anchor been lifted wholly off the ground, we must have been borne past the shore exactly at that rate; but by allowing it to drag along the ground, a friction was produced, by which the ship was retarded one mile an hour; and she was therefore actually carried down the stream at the rate of only two miles, while the remaining one mile of tide ran past, and allowed of her being steered: so that, in point of fact, the ship became as much under the command of the rudder as if she had been under sail, and going at the rate of one mile an hour through the water.

This power of steering enabled the pilot to thread his way, stern foremost, amongst the shoals, and to avoid the angles of the sand-banks; for, by turning the ship's head one way or the other, the tide was made to act obliquely on the opposite bow, and thus she was easily made to cross over from bank to bank, in a zig-zag direction. It sometimes happened, that with every care the pilot found himself caught by some eddy of the tide, which threatened to carry him on a shoal; when this took place, a few fathoms of the cable were permitted to run out, which in an instant allowed the anchor to fix itself in the ground, and consequently the ship became motionless. By now placing the rudder in the proper position, the tide was soon made to act on one bow; the ship was sheered over, as it is called, clear of the danger; and the cable being again drawn in, the anchor dragged along as before. The operation of kedging, as may be conceived, requires the most constant vigilance, and is full of interest, though rather a slow mode of proceeding; for it cost us all that night, and the whole of the next day and night, to retrace the ground which we formerly had gone over in ten hours.

We had by means of this delay an opportunity of seeing the country by day-light; but except at a few chance openings, the distant view was completely shut out by the dense nature of the forest on both banks of the stream.

On reaching the entrance of the river, we fell in with two boats belonging to the United States' ship Constellation, proceeding to Guayaquil. This frigate's draft of water was so great, that the pilots could not undertake to carry her over the shoals, unless she were lightened by the removal of her guns. As this could not be done readily, the captain and a party of his officers had determined to go up in their boats. We were happy to afford them a resting place and refreshment, before their long row, in a dreadfully hot day.

The accidents of a similar course of service had thrown the Constellation and the Conway frequently together, during the last year; and the intercourse which naturally sprung up in consequence, had established an esteem and friendship, which made such a recontre a source of general satisfaction. We learned from our American friends, that they also expected to visit the coast of Mexico, for which we were bound, and we rejoiced at the prospect of again falling in with them. Something, however, interfered to alter their plans, for we never had the pleasure of meeting them again.

We finally left the river and the Bay of Guayaquil on the morning of the 30th of December [1821]. It was no small mortification to us not to have seen Chimborazo, the highest mountain of all the Andes. It was covered with clouds, in the most provoking manner, during the whole of the eight days we have been considerably within the distance at which is is easily discernible in clear weather.

From Guayaquil we stretched off to the westward to the Galapagos, an uninhabited group of volcanic islands, scattered along the equator, at the distance of two hundred leagues from the mainland.

As this is a place of resort for the South Sea whaling ships, I called there to see whether any assistance was required by that important branch of the British shipping interests. But we fell in with only two ships, at one of the most southern islands of the group; after which we proceeded to an island thirty miles north of the line, where I remained a few days to make some experiments with an invariable pendulum of Captain Kater's construction.

I had intended to have made these experiments on a spot lying exactly under the equator, but when we got amongst the islands, a strong current set us so far to leeward in the course of the night before we were aware of its influence, that I found it impossible to regain the lost ground, at least without spending more time than my orders admitted of, and I therefore made for the nearest anchorage within reach.

The spot chosen for the experiments lies near the extremity of a point of land running into the sea, at the south end of the Earl of Abingdon Island, § and forms the western side of a small bay about a mile across. This point is part of an ancient stream of lava which had flowed down the side of a peaked mountain, betweeen two and three miles distant from the station, in a direction nearly north, and about two thousand feet high. The peak slopes rapidly at first, forming a tolerably steep cone, but terminated by a broad and gently inclined base of a mile and a half. The mountain is studded on every side with craters, or mouths, from whence, at different periods, streams of lava have issued, and running far into the sea, have formed projecting points, such as that on which we fixed our station. The western face of the island presents a cliff nearly perpendicular, and not less than a thousand feet high; it exhibits the rude stratification of lava, tuffa, and ashes, which characterises the fracture of ancient volcanic mountains.

§ Now, Isla Pinta.

Abingdon Island is ten or twelve miles in length, the north end being a series of long, low, and very rugged streams of lava; the peak standing about one-third of the whole length from the southern extreme. The rock at different places not far from the station, was found to be full of caverns, into which the tide flowed and ebbed through subterranean channels, the outer crust of the stream having, as frequently happens, served as a pipe to conduct the lava off. It is therefore probable that our foundation may not have been the solid rock; a circumstance which, taken along with the general hollow nature of volcanic districts, and the deepness of the surrounding ocean, renders these experiments not so fit to be compared with those made in England, as with others made on a similar volcanic soil.

It was greatly to be regretted that our time was too limited to allow of our engaging in a fresh series, either at the same island, or on some other lying near the equator: the service upon which the Conway was employed rendering it necessary that our stay should not be longer at the Galapagos than the 16th of January [1822]. But as we anchored at Abingdon's Island on the 7th at noon, there remained barely nine complete days in which everything was to be done. We had to search for a landing-place, which occupied some considerable time; to decide upon a station; to rig our tents; to build the Observatory; then to land the instruments and set them up; and, as we had no time for trials and alterations, everything required to be permanently fixed at once. We were fortunate in weather during the first two days, when our things were all lying about, and our habitations ill assorted; but on the third night it rained hard, and the water, which trickled through the canvass, caused us some discomfort, although we fortunately succeeded in sheltering the instruments. The heat, during the day, was not only oppressive at the time, but very exhausting in its effects; and at night, although the thermometer never fell lower than 73°, the feeling of cold, owing to the transition from 93°, to which it sometimes rose in the day, was very disagreeable.

It was with reluctance that I left the neighbourhood of the equator, without having made more numerous and varied, and, consequently, less exceptionable observations on the length of the pendulum. It would, above all, have been desireable to have swung it at stations whose geological character more nearly resumbled that of England, where Captain Kater's experiments were performed. Thus, the results obtained at the Galapagos, though very curious in themselves, are not so valuable for comparision with those made in this country. The time may come, however, when they may be more useful; that is to say, should experiments be made with the pendulum at stations remote from the Galapagos, but resembling them in insular situation, in size, and in geological character; such as the Azores, the Canaries, St Helena, the Isle of France, and various other stations amongst the eastern islands of the Indian and the Pacific Oceans. The advantage of having it swung at the Cape of Good Hope, and especially at the Falkland Islands, (which lie in the correspondent latitude to that of London,) and at various other stations on the mainland, or on large islands, is still more obvious.

The length of the seconds pendulum at the Galapagos, as determined by our experiments, is 39,01717 inches, and the ellipticity, or compression of the earth, is expressed by the fraction 1/285, where the numerator expresses the difference between the equatorial and polar diameters of the earth, and the denominator the length of the diameter at the equator.

The details of these experiments have been already published in the Philosophical Transations for 1823; and a general abstract is given in the Appendix to these volumes, No. III.

We had no time to survey these islands, a service much required, since few, if any of them, are yet properly laid down on our charts. They are in general barren; but some of the highest have a stunted brushwood, and all of them are covered with the prickly pear-tree, upon which a large species of land-tortoise lives and thrives in a wonderful manner. These animals grow to a great size, weighing sometimes several hundred pounds: they are excellent eating, and we laid in a stock which lasted the ship's company for many weeks.

The most accurate and full account of these curious animals which I have anywhere seen, is contained in a very amusing book, Delano's Voyages and Travels, printed at Boston, in 1807 [sic, 1817]. From the fidelity with which such of their habits as we had an opportunity of observing, are described, I am satisfied with the correctness of the whole picture. We took some on board, which lived for many months, but none of them survived the cold weather off Cape Horn. I preserved one in a cask of spirits, and it may now be seen in the Museum of the College at Edinburgh: It is about the medium size. Captain Delano says,—

“The Terrapin, or as it is sometimes called, the Land-Tortoise, that is found at the Galapagos Islands, is by far the largest, best, and most numerous, of any place I ever visited. Some of the largest weigh three or four hundred pounds; but their common size is between fifty and one hundred pounds. Their shape is somewhat similar to that of our small land-tortoise, which is found upon the upland, and is, like it, high and round on the back. They have a very long neck, which, together with their head, has a disagreeable appearance, very much resembling a large serpent. I have seen them with necks between two and three feet long, and when they saw anything that was new to them, or met each other, they would raise their heads as high as they could, their necks being nearly vertical, and advance with their mouths wide open, appearing to be the most spiteful of any reptile whatever. Sometimes two of them would come up to each other in that manner, so near as almost to touch, and stand in that position for two or three minutes, appearing so angry, that their mouths, heads, and necks appeared to quiver with passion, when, by the least touch of a stick against their necks or heads, they would shrink back in an intstant, and draw their necks, heads, and legs into their shells. This is the only quick motion I ever saw them perform. I was put in the same kind of fear that is felt at the sight or near approach of a snake, at the first one I saw, which was very large. I was alone at the time, and he stretched himself as high as he could, opened his mouth, and advanced towards me. His body was raised more than a foot from the ground, his head turned forward in the manner of a snake in the act of biting, and raised two feet and a half above its body. I had a musket in my hand at the time, and when he advanced near enough to reach him with it, I held the muzzle out so that he hit his neck against it, at the touch of which he dropt himself upon the ground, and instantly secured all his limbs within his shell. They are perfectly harmless, as much so as any animal I know of, notwithstanding their threatening appearance. They have no teeth, and of course they cannot bite very hard. They take their food into their mouths by the assistance of the sharp edge of the upper and under jaw, which shut together, one a little within the other, so as to nip grass, or any flowers, berries, or shrubbery, the only food they eat.

“Those who have seen the elephant, have seen the exact resemblance of the leg and foot of a terrapin. I have thought that I could discover some faint resemblance to that animal in sagacity. They are very prudent in taking care of themselves and their eggs, and in the manner of securing them in their nests; and I have observed on board my own ship, as well as others, that they can easily be taught to go to any place on the deck, which may be wished for them to be constantly kept in. The method to effect this is, by whipping them with a small line when that are out of place, and to take them up and carry them to the place assigned for them; which, being repeated a few times, will bring them into the practice of going themselves, by being whipped when they are out of their place. They can be taught to eat on board a ship, as well as a sheep, or a goat; and will live for a long time, if there is proper food provided for them. This I always took care to do, when in a place where I could procure it. The most suitable to take on board a ship, is prickly pear-trees; the trunk of which is a soft, pithy substance, of a sweetish taste, and full of juice. Sometimes I procured grass for them. Either of these being strewed on the quarter-deck, the pear-tree being cut fine, would immediately entice them to come from all parts of the deck to it; and they would eat in their way, as well as any domestic animal. I have known them live several months without food; but they always, in that case, grow lighter, and their fat diminishes, as common sense teaches, notwithstanding some writers have asserted to the contrary. If food will fatten animals, to go without it will make them lean.

“I carried at one time from James's Island, three hundred very good terrapins to the Island of Masa Fuero; and there landed more than one-half of them, after having them sixty days on board my ship. Half of the number landed, died as soon as they took food. This was owing to their stomachs having got so weak and out of tone, that they could not digest it. As soon as they eat any grass after landing, they would froth at the mouth, and appeared to be in a state of insanity, and died in the course of a day or two. This satisfied me that they were in some sort like other animals, and only differed from them by being slower in their motions; and that it takes a longer time to produce an effect upon their system, than upon that of other creatures. Those that survived the shock which was occasioned by this sudden transition from total abstinence to that of abundance, soon became tranquil, and appeared to be as healthy and as contented with the climate, as when they were at their native place; and they would probably have lived as long, had they not been killed for food. Their flesh, without exception, is of as sweet and pleasant a flavour as any that I ever eat. It was common to take out of one of them, ten or twelve pounds of fat, when they were opened, besides what was necessary to cook them with. This was as yellow as our best butter, and of a sweeter flavour than hog's lard. They are the slowest in their motions of any animal I ever saw, except the sloth. They are remarkable for their strength; one of them would bear a man's weight on his back and walk with him. I have seen them at one or two other places only. One instance was, those brought from Madagascar to the Isle of France; but they were far inferior in size, had longer legs, and were much more ugly in their looks, than those of the Galapagos Islands. I think I have likewise seen them at some of the Oriental Islands which I have visited.

“I have been more particular in describing the terrapin, than I otherwise should have been, had it not been for the many vague accounts given of it by some writers, and the incorrect statement made of the country in which it is to be found. It has been publicly said, that terrapins are common in China, which, I am confident, is incorrect; for I have carried them to Canton at two different times, and every Chinese who came on board my ship, was particularly curious in inspecting and asking questions about them; and not one, I am positive, had any knowledge of the animal before.”

I subjoin the measurement of one terrapin, weighing 190 lbs.

Dimensions of a Terrapin, weighing 190 lbs.
 Inches.
Length of upper shell,43
Breadth of ditto,44¼
Length of belly shell,29
Breadth of ditto,26
Length of the head,  6½
Greatest breadth,  4½
Ditto depth,  3¾
Greatest extent of upper and lower mandible,  3¾
Distance of eye from nose,  1½
Length of neck,31
Circumference about the middle of the neck,  9
From fore part of upper shell to the fore part of belly shell,11½
From after-part of upper shell to the after-part of belly shell,  7
Length of fore leg and thigh,21½
Circumference above the foot,  8¾
Length of hind leg and thigh,24
Circumference above the foot,16
Length of tail,  8½
Depth of upper shell when scooped out,17
Width inside,27
Number of pieces composing the disk,13
Number of pieces in the margin,24
      When alive, weighed . . 190 lbs.
      Quantity fit for use,    . .  84
                Loss,                    106		 

Having finished our experiments, we made sail on the 16th of January 1822 for Panama, but owing to the light winds and calms which prevail in the bay of that name, it was not till the 29th that we came in sight of the coast of Mexico, about one hundred and twenty miles to the westward of Panama.

Appendix No I.

Memoir
on the Navigation
of the
South American Station.

No. X.
 
Guayaquil to the Galapagos.
30th of December 1821, to 5th of January 1822.
(6 Days.)

As the winds between the Galapagos and the main are always from south or S.S.E., there is nothing to be particularly attended to in this passage, except the currents, which generally set to the northward, and increase in strength near the islands. On getting amongst them the greatest care is necessary, to avoid being carried to leeward of the anchorage where it is proposed to stop. In the Conway we were drifted to leeward of James's Island, and could never afterwards regain it. We lay upwards of a week at Abingdon Island, the most northern of the large ones, in a bay at the south end, where we were disagreeably exposed to the S.S.E. winds.

It appeared as if the bad season was about to set in, for several nights we had rain and squalls.

It is to be regretted, that the true geographical position of these islands is still uncertain, and the hydrographical knowledge respecting them so exceedingly scanty. Several of the islands have, it is said, some safe ports, but these are little known, and their resources still less so. We know that an ample supply of terrapins, or land tortises, may be procured at some of the islands, and water is probably to be found at most of them, if diligent search were made. They offer at all seasons a most valuable asylum to the South-Sea Whalers.

Appendix No II.

Table of the Latitudes, Longitudes, and Variation of the Compass of the Various Ports on the Shores of the Pacific Ocean, visited by his Majesty's Ship Conway, in 1820, 1821, and 1822. Extracted from a Hydrographical Memoir, by Mr Henry Foster, R.N.
Name of the Place.CountryLatitude.LongitudeVariation of the Compass Easterly.
East or West of Valparaiso,
by Chronometer.		West of Greenwich.
Gardiner's Island (centre)Galapagos Islands1 22 3218 27 32* 89 58 329° 5' E.
Charles' Island (Saddle pt.)1 20 4018 39 31* 90 10 31
_________ (Post Office Bay)    8 35 35 [sic, 18 35 35]* 90   6 35
Indefatigable's Island, (north end)0 33 36  
James Island, (Sugar Loaf)0 18   018 57 28* 90 28 28
Earl of Abingdon's Island (Conway's anchor.)0 32 21 N.  
Do. (S. W. point)0 32 1918 49 39* 90 20 398 20
* These Longitudes have been connected, by Time-Keepers, with the stations at which occultations were observed.

Appendix No III.

Substance of a Letter to Captain Henry Kater, read before the Royal Society, April 24, 1823, giving an Account of some Experiments made by Captain Hall and Mr Foster with an Invariable Pendulum, during the Voyage to South America, in his Majesty's Ship Conway.

The following pages contain an account of the experiments made with an invariable pendulum, placed in my hands by the Board of Longitude, at the suggestion of Captain Henry Kater, F.R.S., the philosopher to whom the scientific world is indebted for this simple method of determining the figure of the earth. The principle, indeed, was known before; but the practical application, in its present form, is due entirely to his skill and ingenuity.

It was a source of considerable regret to Mr Foster and myself, that we should have visited so many remote places, with such means in our hands, and at last have so few results to produce. The fact, however, is, that the service upon which the ship was employed had no connexion with scientific research; and it was only at casual intervals of active professional employment, that I, at least, could attend at all to inquiries of this nature. These occasional opportunities I owe to the indulgence of Sir Thomas Hardy, Commander-in-Chief in South America, to whose encouragement, in every pursuit having useful knowledge for its object, I stand essentially indebted.

In drawing up the account of these experiments, care was taken to state all the attendant circumstances, and to record in tables every observation in the utmost detail; so that any person wishing to examine the work, may have the best means possible of estimating their value. These tables, which are too voluminous for the present work, will be found at length in the Philosophical Transactions for 1823.

The methods followed for making the adjustments of the instruments, conducting the experiments, and deducing ther results, were those laid down in Captain Kater's paper on the length of the pendulum at the principal stations of the Trigonometrical Survey. We took particular care, for example, always to adjust the diaphragm which is placed in the focus of the eye-piece of the telescope, so that its edges should coincide exactly with those of the extremity of the tail-piece of the pendulum of experiment, according to the precept at page 9 of Captain Kater's paper, read before the Royal Society in June 1819. This adjustment, it may be useful to observe, is rendered more easy and exact, by placing a card, or other whithe object, at a little distance behind the pendulum, when at rest. I also invariably determined the intervals by observing the moment of disappearance of the white disk behind the pundulum, not only in London, but at all the stations abroad.

I am particular in stating these two circumstances, especially the first, from its being so essential to the accuracy of the whole experiment, in all cases where the diameter of the disk and the breadth of the pendulum, though in fact equal, happen to be placed at different distances from the eye, and therefore must appear under different angles; and not, as in Captain Kater's first experiments, (which had another and perfectly distinct object in view,) where the disk and tail-piece were so proportioned, that both occupied the same apparent angle when seen through the telescope.

We were at first disposed to think it might be better to observe both the times of disappearance and reappearance of the white disk, and to assume the mean as the true instant of the coincidence; but we found, by repeated trials, that the time of reappearance was liable to greater or less uncertainty, according to the degree of light, and other unmanageable circumstances; and, having satisfied ourselves that the method of obtaining the intervals by observing the disappearance, was rigorously correct in principle, we adhered to it ever afterwards, as being more simple and infallible in practice. It is meant by this, that in all comparative experiments, such as these were, the method of disappearances is rigorously accurate. It formed no part of our object to determine the absolute length of the pendulum; and therefore we considered it needless to encumber ourselves with a troublesome method of observing, when another, perfectly easy and simple, and equally correct, was within reach. To those who have not considered the subject attentively, and who may be desirous to know what difference it caused, it will be statisfactory to learn, that when experiments are made, at differnt places, by observing the disappearances only, the results are strictly comparative, and, in point of fact, give identically the same results with those deduced from observing both the disappearances and the reappearances, and taking the mean for the time of true coincidence. This assertion is the result of an actual comparison of the two methods.

In making these statements, it is not only due to Captain Kater, but may, perhaps, be useful to future observers, to state, that, after many trials of fancied improvements and simplifications of his methods, both in the conduct of the experiments themselves, and in the subsequent computations, we were finally obliged to acknowledge, in every instance, even where we succeeded, that we had, by more labour, or by more circuitous paths, reached the same point to which his admirable rules would at once have led us.

From having carefully studied Captain Kater's works before leaving England, we had conceived ourselves sufficiently qualified to undertake a course of experiments at once. In this, however, we were mistaken; and the consequence was, that of two extensive series made at Valparaiso, niether proved sufficiently accurate to deserve notice. The experience, however, gained in the course of these operations, enabled us ever afterwards to proceed with confidence. And here it may be well to suggest the advantage which, on future occasions, might arrive from having the whole experiment performed in England, by the person who is afterward to repeat it abroad, not under the hospitable roof of Mr Browne, to whose invaluable assistance every one who has attended to this subject is so deeply obliged, but in the fields, and with no advantages save those which he could carry with him. He would thus, discover omissions in his apparatus, which are not to be supplied abroad, and be aided in surmounting difficulties before he had sailed beyond the reach of appeal.

The first series of experiments was made in London. The next was made thirty-two miles and a half north of the equator, at one of the Galapagos, a group of isialnds in the Pacific, lying upwards of two hundred leagues west from the continent of South America. It was intended that a station should have been chosed immediately under the line, but the ship being swept to leeward in the course of the night by a strong current, this object could not be effected without losing more time than circumstances admitted of being spend in that quarter.

The spot chosen for the experiments lies near the extremity of a tongue of land running into the sea at the south end of Abingdon Island, where it forms the western side of a bay, about a mile across. The point is a stream of lava, which, in former ages, had flowed down the side of a peaked mountain, standing in the middle of this end of the island. The summit of this peak is between two and three miles from the station, in a direction nearly north, and is about two thousand feet high. It slopes rapidly at first, so as to form a tolerably steep cone, terminated by a broad and gently-sloping base of a mile and a half. The sides of the mountain are studded with craters, or mouths, from whence, at different periods, streams of lava have issued, and run down to the sea, where they have formed sharp projecting points, such as that on which we now fixed our station. The western face of the island presents a cliff nearly perpendicular, and not less than a thousand feet high; it exhibits a rude stratification of lava, tuffa, and ashes, materials which characterize the fracture of ancient volcanic mountains. I am thus minute in describing this island, that the reader may be able to judge how far its density may have modified the results of the experiments. It is ten or twelve miles long; the north end being a continued system of long, low, and very rugged streams of lava; the peak standing about one-third of the whole length from the southern extremity, where our station was. The rock, at different places not far from the station, was found to be full of caves, into which the tide flowed through subterranean channels; the outer crust of the stream having, as usual, served as a pipe to conduct the lava off: it is therefore probable that our foundation may not have been the solid rock; a circumstance which, taken along with the general hollow nature of volcanic districts, and the deepness of the surrounding ocean, renders thse experiments not so fit to be compared with those made in England, as with others which may be made hereafter on a volcanic soil.

The range in the temperature, in 24 hours, was from 74° to 91°; and, as we were obliged to place the instruments in a tent, the thermometer rose greatly in the day-time, and fell as much at night, but unfortunately without much uniformity. On the first day of observing coincidences, a set was taken after breakfast, and another before dinner; but it was soon seen that this would confine the observations exclusively to the hot period of the day; it was therefore determined to take in future one set as soon after sun-rise as possible, in order to have a result in which the performance of the pendulum should be modified by the whole night's continued low temperature; and another set toward the close of the day, to obtain a result partaking in like manner of the influence which the whole day's high temperature might have on the length of the pendulum. We also endeavoured so to arrange things, that we might catch a sufficiently long period of uniform temperature during the interval of observing, that all the concidences of each set might be taken with an unvarying thermometer. By these arrangememts it was hoped, that although no one experiment could produce strictly correct results, the errors of the morning and evening observations, being of a contrary nature, might counterbalance one another; that the mean, in short, between observations taken in the hot and in the cold periods of the day, would probably give such a result as might fairly stand by the side of rates deduced from transits of stars, the intervals between observing which, in like manner, included the very same extremes of temperature.

It should be carefully borne in mind, that the real desideratum, as far as respects rate, is not to know what is the aggregate loss or gain of the clock in twenty-four hours; or, in other words, the mean rate; but the actual rate at which the clock is going during the particular period of observing: That is to say, the number of beats, and parts of a beat, which, were the clock to go on uniformly from that instant, would be indicated by its dial-plate, in 24 hours of mean time. As the method of transits of stars, however, gives only the avarage rate, or that due to the middle point of time between the transits, we sought, by the arrangements above stated, to obtain, in like manner, average results, by taking the mean of observations with the pendulum made at the extreme temperatures.

One thermometer was suspended, so that its bulb stood an inch in front of the middle part of the pendulum, while another was hung lower down, between the clock-case and the pendulum. The average temperature at night wa 74°, and in the day-time, from 86° to 90°; the latter, as I have said, depending principally on the state of the sky. The allowance for expansion was made from the deductions which resulted from experiments made by Captain Kater on a similar pendulum.

An astronomical circle, by Troughton, was used as a transit instrument, and was placed in a small octagonal observatory of light pannels, communicating by a door with the tent, that the clock could be seen, and its beats heard, by the observer at the instrument; thus, with the exception of the first day's transits, the time was recorded directly from the clock, without the intervention of a chronometer. The meridian mark was placed near the sea, at the distance of 806 feet; a strong post having been driven into a cleft of the rock, and firmly secured, a screen was nailed to it made of copper, and perforated with a set of holes, from one-fourth to one-tenth of an inch in diameter and readily distinguishable from the Observatory. This fixed screen being made in the form of a box to receive the lamp, it became impossible to misplace the light. The instrument was brought down to this mark, and the level carefully examined, before and after every observation, except with some stars which followed too close upon one another. The sun was fortunately observed at noon every day; and as its rays were never allowed to touch any part of the instrument, or to enter the Observatory, except at the moment of noon, and then only through a small aperture, I had reason to hope that none of the adjustments were, at this observation, ever deranged. As the great alternations in temperature alluded to above might naturally be expected to cause fluctuations in the going of the clock, it was satisfactory to have a series of frequently recurring tests, brought to bear upon this essential particular. As the same precautions were observed at every station, this account of them will apply to the whole series of experiments.

But in order that no higher than a correct estimate be formed of this insulated experiment, it is right to describe the peculiar circumstances under which it was performed. It was above all to be regretted that we were so much limited in time, that we could not engage in a fresh series, either at the same island, or on some other lying nearer the equator: but the service upon which the Conway was employed, rendered it necessary that our stay should not be longer at the Galapagos than the 16th of January. Now, as we anchored at Abingdon's Island on the 7th at noon, there were barely nine complete days in which everything was to be done. We had to search for a landing-place, which occupied a considerable time; to decide upon a station; to rig up our tents; to build the Observatory; then to land the instruments and set them up; and as we had no time for trials and alterations, everything required to be permanently fixed at once. We were fortunate in weather during the first two days, when our things were all lying about, and our habitations ill assorted; but on the third night it rained hard, and the water which trickled through the canvass caused us some discomfort, although we fortunately succeeded in sheltering the instruments. The heat during the day was not only oppressive at the time, but very exhaustive in its effects; and at night, although the thermometer never fell below 73°, the feeling of cold arising from the transition from 93°, to which it sometimes rose in the day, was no less disagreeable.

It was with reluctance that I left the neighbourhood of the equator, without having made more numerous and varied, and, consequently, less exceptionable observations on the length of the pendulum. It would, above all, have been desireable to have swung it at stations whose geological character more nearly resumbled that of England, where Captain Kater's experiments were performed. Thus, the results obtained at the Galapagos, though very curious in themselves, are not so valuable for comparision with those made in this country. The time may come, however, when they may be more useful; that is to say, should experiments be made with the pendulum at stations remote from the Galapagos, but resembling them in insular situation, in size, and in geological character; such as the Azores, the Canaries, St Helena, the Isle of France, and various other stations amongst the eastern islands of the Indian and the Pacific Oceans. The advantage of having it swung at the Cape of Good Hope, and especially at the Falkland Islands, (which lie in the correspondent latitude to that of London,) and at various other stations on the mainland, or on large islands, is still more obvious.