Pacific, in a little cove called El Cacola, where we found nothing in the shape of human habitation, but fell in with a gang of fishermen and a few women, from whom we got a drink of water, but for want of sufficient knowledge of their language, gained no information. The beach in this cove is entirely composed of pulverised sand-stone without a trace of iron.

Here we would gladly have remained for the night, ourselves and mules were so knocked up, but the youngster having found out his mistake, told us that we had still another league to travel; accordingly we again mounted, and after another hour's ride through a gloomy wood, at last reached Port San Juan, the ultima thule of our journey, after having been more than nine hours on horseback. The people of Nicaragua say the distance is only seven leagues, but taking into account all our deviations, we may fairly say that we had travelled three miles over as bad a road as ever was trodden by man or beast.

Having been informed that people occasionally resorted to this place for change of air and sea bathing, we expected to have found a few huts near the beach, but we saw nothing of the kind, and the only human being we met with was an old fisherman, who gave us a scanty supply of water; on the way however from El Cacola, we saw the glimmering of lights at a distance, and may, therefore, infer that there is a village in the vicinity.

In the course of the night we were enabled to get three excellent single sights on each side of the meridian, the mean of which we subsequently found gave a very satisfactory result. We also obtained the latitude by difference of altitude, making this place 11° 46′ south of Nicaragua, but all our endeavours to obtain equal altitudes were frustrated by the impossibility to set the instrument for want of a good light. Friday, 20th, 4 A.M.-Having now obtained the ultimate object of our expedition, we sent the guides for the mules, and in the mean time we employed ourselves reconnoitering this bay, which I at once recognized as the scene of Mr. Bailey's operations, he having shewn me his plan at Grenada; it certainly does not merit the name of port, being ittle more than a large cove, distinguishable from that of El Cacola, by its having near the centre of the beach a swamp which communicates with the sea, and when the tide ebbs, all has the appearance of a running stream of fresh water. The rise and fall of tide is, I think Mr. Bailey told me about twelve feet.

THE SYMPIESOMETER.

Audax at sea, Feb., 1841. SIR. Having frequently heard the remark that the Sympiesometer was too delicate, often falling without any apparent cause, I was induced on a late passage from the Cape, to keep a register every three hours, of the respective height of the barometer with it. It was not long before I discovered that the sympiesometer fell more on an increase of temperature up to 80' than the scale corrected, and from 80 to 90 rose; thus for example, at a temperature of 50° the sympiesometer was + 40 hundredths, at 70° + 20 at 80° or 82° equal, and at 90° it was -20. This will easily be proved by noting the difference between a barometer and sympiesometer, and then placing a candle sufficiently ENLARGED SERIES.-NO. 4.-VOL. FOR 1841.

2 1.

near the sympiesometer, to rise the temperature ten or twenty degrees, It will be then seen that another correction beside the scale, is requisite to reduce it to a mean height, and though barometers are not all marked alike, and the following table may not agree with all in placing the standard at 82°, still it will reduce it to a mean height..

I have applied this correction two voyages since, and I find it answers extremely well, and as it is the mean result of more than 500 observations, I now never look at my sympiesometer without making allowance for the difference of temperature between the observations. When this is done, I believe it to be an invaluable instrument, and superior to the barometer at sea,—inasmuch as all pumping is avoided, and it may be observed with the greatest accuracy. I annex an example of my present method of registering, and an instance of lighting a fire, the increase of temperature causing the line of sympiesometer to fall more than the barometer. Hoping these remarks may be of some service, and looking for some fresh information on the subject,

I am, &c., AUDAX.

[The table alluded to by our correspondent is, we believe, supplied with Adie's instruments, and the example promised with it, (though not received) is perhaps not of so much consequence, as those who use Adie's instrument, of course adopt his table. We have not heard that a similar correction is necessary in the use of Cummings's instrument, alluded to in our February number, but conclude that it must be.-ED.]

ATLANTIC STEAM NAVIGATION.

WE transfer the following letter on Atlantic Steam Navigation, with its accompanying table from the Mechanics' Magazine to our own pages, as it affords useful data for determining the velocities of the great steamers, in making their passages between this country and the United States.

The result from the combined passages, is to New York sixteen days, and home fourteen days twenty-two hours; the mean velocities being outwards eight knots, and homewards 8.6 knots per hour. But if we select the Great Western's passages, we have the mean passage out fifteen days fourteen hours, and home thirteen days fifteen hours; the former average rate being eight knots, and the latter 9-6 knots per hour.

The great iron steamer alluded to in the latter part of the letter, will measure 3,600 tons. She is now plated to her height from forward to within a quarter of her length abaft. She presents a fine hold, with a general form assimilating to the French ships of Mr. Romne. Under canvas she would go like a witch; but whether the screw will produce the same effect remains to be seen. Very sanguine are the expectations from it. She will now have four engines of 250 horse-power each, instead of two of 500 horse-power, as first intended,—and is expected to be afloat about April, 1842.

SIR. The accompanying is a Table I have prepared, of the length of all the outward and homeward voyages of the New York steam-ships during the year 1840. A new steam-ship, the President, was in August last added to the New York line, but her performances have been anything but satisfactory; and after having made two trips out and home, she was found so miserably deficient in power as to compel her owners

to withdraw her altogether for the present. Her want of speed, it seems, is not caused by any defect in the construction of her engines, which do the greatest credit to those eminent engineers, Messrs. Fawcett and Co., of Liverpool, but in their power being so utterly disproportionate to her tonnage; so that when contending against a heavy head wind and sea, as was the case in November last, they are found next to useless. The British Queen's performances, until about the close of the year, were not so inferior to the Great Western's as in 1839. But a comparison of the voyages of these two vessels, made about the same time, and in the same weather, places the performance of the Great Western in a most striking point of view. On the occasions just alluded to, the British Queen left on her outward voyage on the 2nd of November, and arrived at New York on the 22nd, after a twenty-days' passage, with very bad weather during the whole time. The Great Western left on the 7th of the same month, and arrived on the 24th, after a sixteen and three-quarters days' passage; encountered the same sort of weather as the Queen, and yet beat her by four days nearly. On the homeward passages, the British Queen left New York on the 1st of December, and reached Portsmouth on the 22nd, having been just twenty-one days making the passage, and experienced very rough weather. The Great Western left on the 9th, and arrived at Bristol on the 24th, two days only after the Queen, having been, notwithstanding the very tempestuous weather, but fourteen days ten hours at sea, thus beating her by seven days! In this same voyage home the Great Western had continuous easterly gales and head winds for ten days out of the fourteen. The quickest voyage to New York appears to have been that of the British Queen, in rather less than fourteen days. The quickest home voyage was made in July, by the Great Western, in thirteen days eight hours. The longest outward appears to be that of the British Queen, in twenty days', and the same homeward by ditto in twenty-one days. The Royal Mail steam-ships-the first of which, the Britannia, commenced running between Liverpool, Halifax, and Boston in July last,-have made their outward and homeward passages with admirable quickness and regularity. There are four splendid steamers on this line,-viz. the Arcadia, Britannia, Caledonia, and Columbia, each of 1,200 tons, with engines of 440 horse power. These vessels were all built and fitted by the Clyde ship builders and engineers, and I must say do great credit to them. The Arcadia has made two passages out and home, between Liverpool and Halifax. The lengths of the outward have been ten and ten and a half days; and those of the homeward ten and eleven days. The Britannia has made six voyages in all; the three outward occupying respectively thirteen, ten and a half, and twelve and three-quarters days, and the homeward ten, eleven, and thirteen and a half days. The Caledonia, from not coming on the station till September, has made but three voyages; two outward, occupying ten and a half and twelve days, and one homeward eleven. The Columbia* has not yet made a single trip, but will leave on her first outward one in a few days. Much interest will doubtless be excited when the immense iron steamer now building for the Great Western Company is ready for sea, as it will then be seen She has since made her first passage.

what really are the advantages the screw-propeller (with which she is to be fitted,) possesses over the common paddle-wheel. I know not how it may strike your readers, but it does appear to me—a disinterested person in the affair,-a rather hazardous thing on the part of the Company, to adopt an invention, of the success of which they are not as yet fully satisfied. One voyage, however, from Bristol to New York, will be quite sufficient to decide this question.

I am yours, &c.,

NAUTICUS.

Table of the Outward and Homeward Voyages of the New York Steam Ships

for 1840.