they imagined they must become victims to the ambition of this great man. The discovery of this phænomenon, which was then made, has been erroneously attributed to Sebastian Cabot; but the magnetic variation has been turned to account in navigation, and various theories on the cause of it have been advanced. On the subject of its discovery, Hutton says, in his Mathematical Dictionary, vol. ii. p. 550, For it seems there is in the library of the University of Leyden, a small manuscript tract on the magnet, in Latin, written by one Peter Adsiger, bearing date the 8th of August, 1269, in which the declination of the needle is particularly mentioned. Mr. Cavallo printed the chief part of this letter in the Supplement to his Treatise on Magnetism, with a translation; and it is to be wished he had printed the whole of so curious a paper,' &c.

The establishment of the Casa de la Contratacion in Seville, in 1503, Navarete tells us, and the opulence which that city gained from the intercourse of its people with the New World, gave rise to the pursuit of mathematics and navigation there, to a degree that till then was unknown. The Emperor Charles the Fifth established colleges in this city, wherein Sebastian Cabot taught these sciences. The result was, that a multitude of books on navigation were published, a list of which, with their various purposes, may be found in Navarete's historical work. Stimulants such as these, and their results, are alike in all countries, where they are protected by those in authority, and where the interest arising from them is properly divided.

But the safety of the navigator was yet imperfect, and a method was still wanted by which he might find his longitude at sea, and which, although it might not arrive at that degree of precision by which the latitude could be found, should at least afford an approximation to it. For this purpose, various methods were proposed, all grossly defective, until astronomy again came to the aid of navigation. Hipparchus, the inventor of the use of longitude in charts, was acquainted with no other method of finding it, than by eclipses of the moon. Kepler added those of the sun, at the expense of a vast deal of culculation; but each requiring that the observer should remain stationary, their methods were of no service to the navigator. The first person to whom it occurred to find the longitude by means of lunar distances, was Pedro Apiano, in the year 1510; but his method was neglected, because it was deficient of the necessary corrections for parallax and refraction, in consequence of which it gave results that were even more erroneous than those obtained only from estimation. His cotemporary, Reynero Gemma, adopted the same method, but fell into similar errors.

To remove these difficulties, Philip the Third, in 1598, was the first to offer a considerable reward to the person who should discover a method of finding the longitude at sea, that would not only serve to determine the situation of the ship, but would also improve the state of the charts. The Dutch Government next

followed this example, and in 1714 the British Government voted £2000 to perform experiments, and a reward of £10,000 to the person who should find a method of ascertaining it within one degree of the truth; also £15,000 if it should come within two-thirds of it, and £20,000 should it come within half a degree; but if the method employed was that of the distance between the moon and sun, or stars, £5000 was offered to bring it within fifteen minutes of error in the distance, which is equal to seven minutes of longitude.* With these encouragements, men of science applied themselves to gain the promised reward in Spain, France, and in England, as well as in other parts of the world. They invented various instruments and methods; but the results obtained did not fall within the proposed limits.

The application of Jupiter's satellites by Galileo, previous to this, for determining the longitude, was more effectual; but these observations, so valuable for places on land, were unavailable at sea.

The Spanish pilot, Andres de San Martin, in the voyage which he made with Magalhaens, had already employed the method with which Ruy Fallero+ had supplied him, of determining the longitude by lunar distances; but the results he obtained, not being, as he considered, correct, with much discernment he attributed it to errors in the tables of the sun given in the almanack, satisfying himself, that while they remained so, the problem would never be determined. At the end of this century, Pedro Sarmiento de Gamboa, one of the most expert navigators of his day, obtained the longitude at sea by the lunar distances, which he measured with an instrument of his own making; and his results were so good, that he was enabled to correct the reckoning of his ship, which he ascertained amounted to 220 leagues of error.‡ But his invention was lost, as he did not make it known.

Gemma Frisius is the first who mentions the use of timekeepers; and, in 1665, the first experiment was made in a voyage to the coast of Guinea, by Major Holmes, with a watch made by Huygens. With this, the longitude of the island of Fogo was obtained with tolerable precision. Sully followed up the art, and, in 1714, published a work on finding the longitude at sea by means of chronometers, and continued his studies at Paris. Julian de Roy was his scholar; and the son of this latter, and M. Berthoud, carried on the subject with more success than had hitherto been known.

In 1726, Mr. Harrison produced a chronometer, the error of which did not amount to one second in the space of ten years. In 1736, it was sent to Lisbon, and corrected the reckoning on the voyage as much as a degree and a half. Thus encouraged, he made successively three watches, which were completed in the years 1739, 58, and 61; the last being so excellent, that the GovernHutton. + Herrera. Decadas de Indias. ↑ Sarmiento. Viage al Magallanes, 1579, y 80.

ment offered to send it on a voyage to the West Indies. The island of Jamaica was fixed on, and his son embarked in 1761 with the chronometer; and, on his arrival, the longitude shown by it did not differ from that obtained by astronomical observation more than a minute and a quarter." Among those who have done most towards bringing these machines to perfection, are Kendal, the next to him is Arnold, whose modern improvements have been justly the theme of admiration; and Mudge, Earnshaw, and others, have each operated with success.

It is said that the first person, who recommended the method of finding the longitude by the lunar distances of the stars, was John Werner, of Nuremberg, who printed his first work on the Geography of Ptolemy, in 1514. But the invention of the quadrant by Hadley, and the corrections which the tables of the stars had received from Mayer, of Gottingen, brought it to that state, which it had been the object of centuries to attain. The astronomers of Europe continued their improvements of the tables of the sun, moon, and Jupiter's satellites, as well as the position of the stars, which they have at length brought to the high degree of perfection in which they now are. With the assistance of these, the navigator crosses the ocean, and reaches his destined port with nearly as much certainty as the traveller on land, differing only from him in expedition.

With the progress of these auxiliaries, Hydrography continued improving, but not to that extent that it should have done. This delay arose from a fear of spreading the knowledge of coasts, the surveys of which were preserved in manuscript. Charts were printed of every known coast, as matter of speculation, with different dates, copied from each other, excepting a few alterations here and there, that were sometimes fatal; till, at length, the various maritime states of Europe, finding where their real interest lay, and aware of the benefit that would result to humanity, in perfecting Hydrography, despatched expeditions with this object, and established depots, where the results of their operations might be analyzed; and thus has Hydrography arrived at a state of perfection, which it could not possibly have attained but by such. means. Much, however, yet remains to be done; but the interest is so general, and more particularly in this country, that we venture to hope for its completion. To effect so desirable a purpose, we contribute our humble endeavours, satisfied, that if the zeal be continued with which other countries, as well as this, have of late years followed up this important subject, we shall soon see completed, that great object, which it has been the constant solicitude in former ages to accomplish.

* Hutton.

[The above Introduction for this work, is translated from the Spanish MS. of Don Felipe Bauza, late Hydrographer at Madrid, Foreign Member of the Royal and Geographical Societies, and Associate of the Astronomical Society of London.]

HYDROGRAPHY.

Note.-All Bearings are Magnetic, unless otherwise stated.

1. THE VIRGIN Rocks, Bank of Newfoundland. 46° 26' 15" N. LONGITUDE 50° 56′ 35′′ W. 41 fathoms.

LATITUDE
Soundings

THAT the situation of these rocks should have remained uncertain, and even that their existence should have been doubted, to a very recent period, affords an instance of one among the many difficulties with which hydrographers have to contend in the construction of charts. Although repeatedly sought for, they were known only to a few fishermen, who frequent the Banks of Newfoundland, until the enlightened views of Vice-Admiral Sir Charles Ogle, Bart., for the safety of our North American traders, led to their complete discovery. To the laudable exertions of this officer, while commander-in-chief on the North American station, navigators are indebted for ascertaining their correct position, besides various other important and valuable observations on that coast. In the month of July, 1829, the Inspector, tender, under the charge of Mr. Edward Rose, Master in the Navy, accompanied by His Majesty's Sloop Manly, Lieut. (now Com.) Bishop, were sent by Sir Charles Ogle, to look for and determine the position of these rocks.

His Majesty's Sloop Inspector was anchored about one hundred fathoms to the north-east of the shoalest part of the rocks, in the above position. The observations were made with a circle by Worthington and Allen, and two chronometers, the latter with a rate six days old from Halifax. Their meridian distance from Halifax was found to be 12° 42′ 6′′ E. and the longitude of the rocks depends on Halifax dock-yard, which is supposed to be in 63° 38′ 41′′ W. of Greenwich. The Inspector lay at anchor forty-eight hours, during which time the above result was obtained from a series of observations with a well-defined horizon and favourable weather.

Mr. Rose describes the rocks as extending in an irregular chain, or cluster, 800 yards in the direction of N. E. by E. and S. W. by W., their breadth varying from 200 to 300 yards. They were distinctly seen under water, particularly a large white mass of rock, in 4 fathoms, having 5 and 6 fathoms round it. The shoal was traced in 7 fathoms, on detached rocks, near the edge of it, having

deeper water between them. On the southern edge of the shoal, from S. E. to W., the depth increases gradually to 30 fathoms, at the distance of half a mile from the shoalest part. The same depth was found to the N. W. and N. E. of the shoal, at the distance of one-third of a mile, and also between N. E. and S. E. at the distance of one mile.

The bank on which the Virgin Rocks are situated, was found, by Mr. Rose, to extend four miles and a quarter, in an E. by S. and W. by N. direction, and two miles and three-quarters in its broadest part, the depth being regular from 28 to 30 fathoms. Beyond these limits, the depth increased suddenly to 39 and 43 fathoms. The current was found setting to W.S.W. at the rate of one mile per hour over the shoal, with a confused cross-swell.

The Manly, whilst at anchor on the bank, was obliged to strike her top-gallant masts; and the swell was so considerable, that the vessel rolled the muzzles of her guns under water. The Manly remained at anchor one night, and, on getting under way in the morning, the chain cable broke in the middle, owing, it was supposed, to the violent friction which it had undergone against the rocks. In an easterly gale, which would be attended with the whole swell of the Atlantic ocean, no vessel could pass over these rocks. They lie in the direct track to Cape Race, Newfoundland, the point which vessels, bound to Quebec, generally endeavour to make.

The following accounts of the VIRGIN ROCKS, previous to their discovery by Sir Charles Ogle, afford some further particulars relating to them:

By Captain Cummings.

"Lat. 46°. 27′. N. lon. 51°. 8'. W. Soundings were had in 23 fathoms, one mile to the northward. Captain Cummings states these rocks to be of a triangular shape: breakers very heavy. The bearings from Cape Broyle S.E. S. 80 miles."

By Captain Kemp.

"Lat. 46° 30' N. lon. 50° 51' W. Cape Broyle, S.E. S. 84 miles."

By Mr. Moore, of Ferryland.

"Mr. Moore has frequently been on the shoals, and had vessels fishing on them. E.S.E. from Cape Race, by compass, are the Virgin Rocks, near and around which you will have 40 fathoms. Immediately on them he has, in his long-boat, held one end of the kelp in his hand, while the other end was fast on the ground, in about 2 or 3 fathoms water. From Ferryland Head the course is S.E. by E. by compass, 75 or 80 miles: E.S.E. by compass, distant 3 or 4 leagues from them, are the Scotch rocks. This information, I trust, will enable you to ascertain their particular situation; a thing which, when the bank fishing was prosecuted extensively from hence, was as well known to the masters of the bankers as any particular part of the coast; and indeed appears to have been their general and invariable resort during the months of June and July; that is, the caplin season."