whose mildest provisions sanctioned poison and the dagger, upon even the suspicion of crime, wielded the destinies of Venice; and yet she preserved the name and outward semblance of a republic. Her citizens were seized, tortured, imprisoned, secretly tried and executed, and yet they boasted of freedom, the supremacy and purity of their laws, and of the wisdom of their institutions. But with all the imperfections and deformities of her political and moral system, sanctioning, as they unquestionably did, the darkest crimes, and the most terrible punishments, Venice, during the long line of centuries through which she flourished, stood in the front rank of nations, surpassed by few in the justice and humanity of her government, excelled by none in her knowledge of the arts and sciences, and in the perfection of her manufactures, and outstripping all in the magnitude of her commercial interests, and in the extent and splendor of her maritime power.

ART. II.-THERMOMETRICAL OBSERVATIONS AS CON. NECTED WITH NAVIGATION.

THE UTILITY OF THERMOMETRICAL OBSERVATIONS IN ASCERTAINING THE RELATIVE HEAT OF THE SEA-WATER FROM TIME TO TIME, TO DISCOVER THE PASSAGE OF A VESSEL THROUGH THE GULF STREAM, AND FROM DEEP WATER INTO SOUNDINGS,-BANKS AND ROCKS, IN TIME TO AVOID DANGER, ALTHOUGH, OWING TO TEMPESTUOUS WEATHER, IT MAY BE IMPOSSIBLE TO HEAVE THE LEAD, OR OBSERVE THE HEAVENLY BODIES ;—AND ON PRESERVING VESSELS FROM LIGHTNING.

THE Merchants' Magazine has been so well conducted, and contains so much useful matter, which "comes home to the business and bosoms of mankind," that I am pleased by making it the vehicle of my remarks upon two of the most important subjects to which the attention of the nautical and mercantile community can be called.

The first head of my paper is the title of one which was read before the American Philosophical Society of Philadelphia, in the year 1790,* by the late General Jonathan Williams of the United States army, whose

* Trans., vol. II, p. 82.

+ I cannot permit this opportunity to pass without bearing testimony to the great merits of this excellent man. Like his relation Dr. Franklin, the tendency of his thoughts and actions was utility to his fellow creatures, to whom he also set an example of refined manners, uprightness of conduct, and good will, which can never be forgotten by those who had the happiness of his acquaintance. He entered the American army in the year 1801, and rose to the rank of colonel of engineers. It is to him that our country is indebted for the idea of the military academy at West Point, and for its organization, a task of no ordinary difficulty. His admirable, mild, but firm discipline, subdued tem. pers disposed to be unruly, eradicated bad habits from among the pupils, while he stimulated all to an honorable ambition to excel in their private deportment and in their official duties. His government was parental, and he was beloved as a father by the youth under his command. Science has seldom been applied more beneficially to for. warding the business of mankind, than in the instance of Mr. Williams' experiments,

attention was first called to the subject under consideration, from having made, in the year 1785, by the direction of his relation Dr. Franklin, the experiments mentioned in his description of the course of the Gulf Stream, an account of which was annexed to his "maritime observations," addressed to the learned A. Le Roy of Paris,* and he determined to repeat these experiments in his future voyages. Accordingly, in one from Boston to Virginia, two from Virginia to England, three from England to Halifax, and four from Halifax to New York, he kept regular journals of the heat of the air and water at sunrise, noon, and sunset, and by consulting these, and the observations made at the dates written, together with the tracks of the ship's way, marked on the chart annexed, it will not only appear that Dr. Franklin's account of the warmth of the Gulf Stream is confirmed, but also that banks, coasts, islands of ice, and rocks under water, may be discovered when not visible, and when the weather is too boisterous to sound, with no other trouble than dipping the thermometer into the sea-water. His experiments also establish the following facts.

1. That the water over banks is much colder than the water of the main ocean, and it is more cold in proportion as it is less deep.

2. The water over small banks is less cold than that of large ones. 3. The water over banks of the coast, that is, those immediately connected with the land above water, is warmer than that over those which admit deep water between them and the coast; but still it is colder than the adjacent sea.

4. The water within capes and rivers does not follow those rules; it being less agitated, and more exposed to the heat of the sun, and receiving the heat from the circumjacent land, must be colder or warmer than that in soundings without, according to the seasons and temperature of the atmosphere.

5. The passage, therefore, from deep to shoal water may be discovered by a regular use of the thermometer before a navigator can see the land; but as the temperature is relative, no particular degree can be ascertained as a rule, and the judgment can only be guided by the difference. Thus, in August, Mr. Williams found the water off Cape Cod to be 58° of Fahrenheit, and at sea 69°; in October, the water off Cape Cod was 48°, This difference was equally a guide in both cases, and at sea it was 59°. though the heat was different at different seasons.

The chart and first journal of Mr. Williams, from Boston to Virginia, shows that the water on the coast of Massachusetts was at 48°; at sea, between the coast and the stream, 59°; in the Gulf Stream, at its edge, 67°; between that and the Virginia coast, further south, 64°, and in soundings on that coast, 56°.

and every navigator is under lasting obligations to him, for the knowledge of the means of securing their safety at times when the compass, the log, or the quadrant, nay, the organs of vision, avail them nothing.

* Trans. Amer. Philos. Soc., vol. II,

p. 328.

+ The increased heat of the Gulf Stream, although doubtless familiar to navigators, it is believed was first noticed in print by Dr. Blagden in his paper on the subject, in the Transactions of the Royal Society of London for 1781. On the 30th September, 1777, the water was at 76 deg. of Fahrenheit, and eleven deg. above that of the sea, before Mr. Strickland found this difference to be even the vessel came into the current.

greater, as will appear presently.

The second journal from Virginia to England, shows that the water on the coast of Virginia, in December, was at 47°; between the coast and the stream, 60°, and in the stream 70°; near the banks of Newfoundland the thermometer fell from 66° to 54°; passing these it arose again to 60°, and then continued a very gradual descent as he went north, till he struck soundings, when it was at 48°.

In Dr. Franklin's journal of November, 1776, the thermometer fell 10°; near the banks and after passing them, it arose nearly to its former height. This agrees with Mr. Williams' journal nearly in the same place, made nine years afterward.

The third journal from England to Halifax shows the changes in the heat of the water, as he sailed over the banks and deep water alternately, with an accuracy that exceeded his expectation, the land appearing as the thermometer indicated an approach to it.

The journal from Halifax to New York, not only shows the variety of depths passed over, but indicates the inner edge of the Gulf Stream.

On the chart annexed to Mr. Williams' paper, the tracks of his several passages are marked, with the daily heat of the water, by which the variations on the approach to land may be seen at one view. The edge of the Gulf Stream is also traced, according to the experiments, as far as the banks of Newfoundland.

In addition to his journals, Mr. Williams has subjoined an account of some experiments on fish, (cod and halibut,) which show that their heat was 16° colder than the water at the surface, from which it may be supposed that the water at bottom is in proportion colder than that above: air 57°, water 52°, fish's belly 37°. Lat. 44° 52′; (July, 1790 :) air 57°, water 53°, fish's belly 37°.*

The difference of heat which marks an approach to land, he found to be 6 degrees in three hours run, and long before the vessel was near enough to be in danger. In a former voyage, it was found that near the coast, in very hot weather, the water at the bottom, in 18 fathoms, was 12 degrees colder than at the surface. This difference of heat is more remarkable in winter than in summer, for Captain Billings of Philadelphia, in a voyage to Oporto, in June, 1791, found that the water on the coast was 61°, and in the Gulf Stream 77°. By Mr. Williams' journals it appears that, in November, 1789, the water on the coast was 47°, and in the Gulf Stream at 70°. Returning towards the coast of North America, Captain Billings discovered his passage across the Gulf Stream by a sudden fall in the mercury of 5° from noon to night; and about 5° further west, by a further fall, in the space of 8 hours, he discovered the coast, where he got soundings before he saw the land.

On the subject of the utility of the thermometer at sea, Captain Thomas Truxton, the well-known United States naval commander, wrote to Mr. Williams the following letter:

* These experiments were made by an officer of the British packet Chesterfield, Captain Schuyler, July 11, 1790. The preceding day, in another experiment, the temperature of the air was 57 deg., that of the belly of the fish 39 deg., water 52 deg., depth 46 fathoms. These results were communicated to Mr. Williams by Cap. tain Schuyler.

+ Trans. Amer. Philos. Soc., vol. III, p. 194.

Extract of a letter from Captain Thomas Truxton to Jonathan Williams. "PERTH AMBOY, 12th August, 1799. "Your publication will be of use to navigation, by rendering sea voyages secure, far beyond what even you yourself will immediately calculate, for I have proved the utility of the thermometer very often since we sailed together,* not only in crossing and re-crossing the Gulf Stream that runs along our coasts, but in the Ethiopian, Indian, Arabian and Chinese seas, Gulf of Bengal, Gulf of Siam, the various straits in the east. ern world, and in many other parts of the globe.

"It will be found a most valuable instrument in the hands of mariners, and particularly so to those who are unacquainted with astronòmical observations, and calculations for determining the longitude at sea; these particularly stand in need of a simple me. thod of ascertaining their approach to, or distance from the coast, especially in the winter season; for it is then that passages are often prolonged, and ships blown off the coast, by hard westerly winds, and vessels being in the Gulf Stream, without its being known; on which account they are often hove to, by the captains supposing themselves near to the coast, when they are very far off, and by this means favorable spirts of wind are lost. On the other hand, ships are often cast on the coast by sailing in the eddy of the stream, which causes them to outrun their common reckoning. Eevery year produces new proofs of these facts, and of the calamities incident thereto."

Mr. Williams gives the following important directions to navigators :

DIRECTIONS TO NAVIGATORS.

"Take with you at least three thermometers, for fear of accidents. Let them be kept in one place some days previous to your sailing, in or der to try their uniformity. The plate should be of ivory or metal, for wood will swell at sea, and as the glass-tube will not yield, it is for this reason very liable to break; bell-metal is the best. Let the instrument be fixed in a square metal box, the bottom of which, as high as the mark 30°, should be water-tight, so that in examining the degree of heat, the ball may be kept in the water; the remainder of the length should be open in front, with only two or three cross-bars to ward off any accidental blow, like the thermometer used by brewers. Fix one instrument in some part of the ship in the shade, and in open air; but as much out of the wind, and in as dry a place as possible. The after part of one of the after-stanchions, under the quarter-rail, may answer, if no better place can be found.

"Let the second instrument be neatly slung with a sufficiency of line to allow it to tow in the dead water of the wake.

"Put the third away safely in your chest, to be ready to supply the place of either of the others.

"When you make your observations, begin by noting the state of the air from the instrument on deck. Throw the other out of the cabin window, and let it tow two or three minutes, then draw it up and examine it the instant you can bring it to your eye, with the ball still in water, and note the degree. This is a necessary precaution, for the mercury will soon fall when the thermometer is wet, especially if exposed to any wind. When you examine the water at night, take care not to heat the instrument by a candle, which should be always in a lantern; do not touch the tube, nor breathe upon it, while you examine it; lest you should communicate heat by the touch, or take it away by causing an evaporation, which is the effect of blowing upon a wet thermometer.

"Endeavor to make all your experiments in a uniform manner; do not

* Captain T. commanded the ship in which Dr. Franklin and Mr. Williams were passengers from Europe to the United States, in the year 1785.

try the water one day out of the cabin windows, another over the side, or in a bucket, but keep to one steady rule; it is not so material which way you do it, as it is to do it always the same way. If a bucket be used, let it tow long enough to take away its heat, for the cook may have had it full of hot water.

"Pay constant attention to the changes in the temperature of the air, and compare them daily with the changes in that of the water. This will account to you for the alterations on the surface of the sea, (especially in calm weather,) which naturally follow the alterations in the incumbent atmosphere. The difference between deep water and soundings will, under the same temperature of the atmosphere, still be the same. If, when in open sea, you should perceive a small change in the water, without be ing able to account for it by an alteration of latitude, or of the weather, you may suspect a current from the northward if colder, from the southward if warmer; and as circumstances may permit, you will do well to ascertain it.

"Compare your observations from time to time with those mentioned in the journals and noted on the chart, and if you find any difference when in the same situation, repeat your experiments, so as to be sure that the error is not on your side.

"Although it is not pretended to give accurate accounts, from the few experiments that have been made, it is presumed that the following will be found near the truth.

"FROM THE COAST OF EUROPE.-From the channel of England to the Tagus it will be generally found, that the water over soundings is about three degrees colder than at sea. And that the first symptom of soundings is at a great distance from the land, for the coast, (unlike that of America,) approaches from imperceptible depth to soundings so gradually, that it is not easy to say when you can get the ground. But were you to approach the rocks of Scilly, western coast of Ireland, Orkneys, &c., the alteration would probably be sudden and very decisive.

"ON THE COAST OF NORTH AMERICA.-At the edge of the Grand Bank, the water is 5 degrees colder than the deep ocean to the eastward. The highest part of the Grand Bank is 10° colder still, or 15° colder than the ocean eastward.

"As the banks deepen between them and the coast of Nova Scotia, the water grows about 6° warmer, till you get quite within them, when it rises to about the temperature of the deep ocean without; on soundings, the mercury will again fall to the temperature of the inner banks. So that, in coming from the eastward, a fall of 5° will indicate your entrance on the edge of the Grand Bank, and a further fall of 10° will indicate your being in soundings. Passing the summit of the banks, a rise of 6° will show the western edge of the Grand Bank, and a further rise to the temperature of the deep ocean without, will indicate the deep water within the banks. When the mercury falls again to the temperature of the inner banks, you strike soundings on the coast of Nova Scotia.

"An important observation occurs here. The Isle of Sable is a little bank of sand above water, which receives heat readily from a hot sun and communicates it rapidly to the shoals under water, upon the principle mentioned as to land-locked places. If, therefore, you come too near that island in hot weather, the thermometer will probably vary from these rules; in that case, you may get bottom. If, however, the previous ob