be seen, and if a power of 3000 could under such conditions be effective, 12 feet bands might be visible. How much of this the really, unclear' condition of our atmosphere will allow to be realized, remains to be determined by experiment.

On the Surface Temperature and Great Currents of the North Atlantic and Northern Oceans. By the Rev. WILLIAM SCORESBY, D.D., F.R.S. L. & E., Cor. Mem. of Institute of France, &c.

The currents of the ocean, exerting as they do so great an influence on the condition of the air, the earth, and of the sea itself, constitute a subject of very important consideration in physical geography, and, indeed, in general science; and they are specially interesting as a compensating instrumentality against the extremes of condition to which the fervid action of the sun in the tropics, and its oblique and inferior action in the polar regions, tend,—an instrumentality serving not only to moderate the extremes of temperature, but to render the general surface of the earth more favourable for the comfort and benefit of its inhabitants.

Our knowledge of the great currents of the ocean has hitherto been mainly derived from the observations of navigators on the differences found betwixt the ship's actual position during the voyage, as determined by celestial observations, and that of the daily reckoning from the course steered and distance run. The results of observations of this nature, extensively collected and collated, are found in the labours of Major Rennell, Lieutenant Maury of the United States Navy, Mr. Findlay, &c. Dr. Scoresby then noticed the errors to which this mode of investigation is ordinarily subject from defects in the log, compass action, and steerage of the ship-all of which are liable to render the determinations uncertain unless where numerous observations are found accordant, or those in different voyages made mutually corrective.

The process he had used, affording data for the present paper, consisted mainly in the observing, during the progress of the ship, of the differences occurring in the surface temperature of the ocean, which in many cases were such as to give unquestionable indications of currents coming from different regions, though not generally serving to determine the exact direction or velocity.

His observations would refer, in the first instance, to the currents of the North Atlantic, as indicated by thermometric changes and peculiarities within a belt of ocean about 220 miles in average width, extending in a W. by S. direction from the entrance of the English Channel to Long Island, proximate to New York.

Four transatlantic passages made by himself, with numerous voyages by Captain Jos. Delano, a scientific American and excellent observer, who had furnished him with the results of many of his researches, had supplied the materials for the present determinations. These materials, extending to about 1400 observations (usually taken six times a day) on the temperature of the sea, being placed on a chart along with the projection of the ship's track on each voyage, were then tabulated, and the leading indications finally represented in a diagram (Plate I.) before the Section.

Of thirteen passages tabulated, seven were made in the spring of the year, two in summer, one in autumn, and three in winter. Taking the middle day of each passage, the mean day at sea was found to be May 18-19, a day fortunately coincident, with singular nearness, with the probable time of the mean oceanic temperature.

The results indeed thus derived could not be considered as complete, nor the normals of surface temperature in the different sections of the route conclusive; yet they exhibited, in certain particulars, facts of considerable interest and importance. The mean surface temperature of the whole range of observations was 56°, the mean temperature of the air in the same passages (the result of 1000 to 1500 observations) being 34° 2, indicating the prevalently received fact of the general superiority of the temperature of the sea over that of the atmosphere.

Though the observations were not sufficient for conclusive determinations of the effects of latitude and season on the surface temperature, yet they obviously yielded something sufficiently proximate to be not unworthy of notice, especially for the early part of the passage westward, from longitude 12° to 36° W., and latitude 50° to 46°. And within this limited range, the observations under discussion seemed, in respect of latitude, to indicate an increase of the surface temperature, steering W. by S. from

the English Channel, of about three-quarters of a degree for each degree of latitude southward in winter, and a change of about a degree of surface temperature for each degree of latitude in summer.

In regard to the effects of season (taking the average) within the same portion of the transatlantic passage, there appears to be a range of 9° or 10°; the highest being about 61° in July and August, and the lowest 51° to 52° in January and February. The analyses of the observations on the various passages yielded, as to changes in the surface temperature, betwixt 12° and 30° W., something like the following series :

The atmospheric changes for the same range of ocean may thus, perhaps, be proximately represented :

1

In specifying the general results of all the observations on the oceanic temperature, we find the first and leading fact to be, a division of the transatlantic belt into two characteristic portions of nearly equal extent, differing, in a striking and singular manner, both in their ordinary temperatures, their extremes, and their changes.

Thus for nearly half the passage across from England, that is, as far as longitude 38° W., in a W. by S. direction, the surface temperature was not found to descend below 50° even in the winter passages, nor to rise in any part of the year (as far as the observations go) higher than 66°. But on reaching 42° W. a temperature of 44° was met with, and at 48° to 50° W. longitude a minimum of 32° was not uncommon, with a maximum sometimes reaching to 69°. Further west, in 58° to 60° longitude (the mean latitude being about 42° N.), along with a minimum temperature ranging from 32° to 42°, a maximum was found as high as 74°. From this meridian to 72° W. similar differences of temperature, except near the American coast, were found to be prevalent.

In regard to mean differences of the extremes of temperature, taking the averages of all the observations within meridians of 2o in width, the results are still more striking; for in the first half of the passage, going westward, we find a mean range of surface temperature, for each 2o of longitude, of only 1103; whilst in the western half the mean range extends to 29°.7. Within the first half, too, where the extremes of temperature of the whole section were found to differ only 19°, the difference betwixt the highest and lowest temperature observed in the second or westerly half, reached to 42°.

This diversity of temperature clearly pointed out the two great and well-known oceanic currents-one from the tropics, the other from the Polar regions-meeting, coalescing, and interlacing within the range of the belt of waters referred to; the former current yielding an occasional warmth of 20° to 22° above the mean atmospheric temperature, and the latter a frequent cold as much below it.

But the phænomena may be rendered more intelligible and instructive if we note the appearance and trace the progress of the more marked alternations in sailing from the English Channel westward; say from longitude 12° W., in the mean latitude of 50° N., to that of 72° W., in the 41st parallel. This belt, extending to 60° of longitude, may be conveniently taken in six decimate sections, as represented in Plate I., several of which, it will be seen, afford peculiar and characteristic differ

ences.

The first three of these decimate sections exhibit, for the most part, a striking uniformity of character; for as far, at least, as longitude 38° W. no particular in the differences of surface temperature strikes us, except a gradual rising of the means, within two degrees' space, from 52°.9 to 58°7, during a descent in the mean latitude from 50° to 46° N. But in longitude 38° to 42° W. the range of oceanic tem

perature obtains the first marked increase, indicative of a slight action of a current from the southward.

the

In the fourth decimate section, 42° to 52° W., however, the indications respectively of the two great currents of the North Atlantic become striking and characteristic. Beyond the meridian of 42°, where the cold current from the north becomes first decided, an increase of its prevalency, gradually becoming more and more conspicuous, is observed. Thus in the two degrees' space, from 42° to 44° W., the somewhat low temperature of 44° was only observed in one out of thirteen passages ; but in the next two degrees a like moderate fall of temperature (about 7° below the inean) occurred in three or four of the passages; in the next meridional stripe, cold water was met with in eight of the passages (four or five falling from 10° to 16° below the mean); in the next, the cold water occurred in nine or ten passages (six falling 10° to 24° below the mean); in the next stripe, longitude 50° to 52° W., cold water was met with in eight passages (five falling 12° to 22° below the mean). Within the same section, 42° to 52° W., very perceptible marks of an ascending tropical current occurred, yielding, in alternations with the cold water from the north, an occasional warmth of 66° to 68°. The prevalency, however, of the occurrence of warm water in this position of the Atlantic appears from the observations tabulated to be in reverse order (when sailing westward from longitude 42°) to that of the cold current; the first two-degree stripe presenting a rise of from 63° to 68° in six passages; the next, a rise of similar extent in five; the next, a smaller rise in four; the next, less marked in three; and the last, 50° to 52° W., in four, but still less marked. Hence from these observations it appeared, that the greatest prevalence of the polar currents (betwixt 42° and 52° W.) is within the meridians of 46° and 52o, and of the warmer current in 42° to 46° W.

It is within this meridional section mainly, corresponding in its central part with the eastern edge of the great bank of Newfoundland, in which the icebergs and drift ice from the north are usually met with; so that the prevalence of a descending polar current obtains actual demonstration.

The fifth decimate section, reaching from 52° to 62° W., is found to be equally characterized by peculiar phænomena as the one preceding it. The general prevalence of the descending polar current is shown by the minimum temperature of each meridional space of 2o, ranging betwixt 32o and 42o, with a mean of the five minima of 37°.2. The prevalence of an ascending current from south-westward is, in like manner, shown by the occurrence of a maximum surface temperature ranging betwixt 63° and 74°, with a mean of the five maxima of 68°9.

But the characteristic features of this fifth decimate section were found to consist in the suddenness of the changes of the surface temperature and the various alternations, indicative of singular interlacings of warm and cold water.

In a passage in the " Patrick Henry" in May 1844, made by Dr. Scoresby, these sudden and alternating changes were remarkably prevalent. Thus when in longitude 57° 0' W. (lat. 41° 31' N.) the surface temperature, at 8 A.M. of May 17th, was found to be 60° 5; but after sailing W.N.W. (true) 10 miles, it was found to be 50°, and at noon 16 miles further on the same course 46°. At 2 P.M. of the same day, longitude 57° 55′ W., the sea was still at 46°; but at 4 P.M., after 15 miles' sailing W.N.W., it had risen to 57°, and in 15 miles further in the same direction it was found to have fallen to 42°! The next day, May 18th, presented further remarkable changes. At 8 A.M., longitude 59° 52′ (latitude 42° 8' N.), the surface temperature was 46°; but at 10 A.M., 15 miles W. S., it had risen to 61°, a change of 15° in two hours! At midnight, again, of the 19th-20th the sea was at 50°; four hours afterwards, 26 miles to the S.W. by W., it was 63°.

Within this decimate section the cold or polar current was found to be chiefly prevalent in the first and last of the two-degree spaces, but the most so in the last, that is, in longitude 60° to 62° W.; and the most prevalent examples of the Gulf-stream appeared within the meridians of 58° and 62° W.

The sixth and last section of the belt of waters traversed in the transatlantic passages under discussion, is found to be characterized, especially within the three westernmost spaces, 66° to 72° W., by a singular depression of the surface temperature generally, the mean temperature of all the observations registered on the chart being 49°4, and of the last three stripes 46°7. As some of the voyages, however,

here failed, the mean of the registered observations may be a little too low; but the obvious deduction nevertheless remains untouched, of the descent of a polar current within the tract of the Gulf-stream by the coasts of New England.

The relations of the Polar current and Gulf-stream, as thus indicated by the analyses of thirteen transatlantic passages generally, change, it should be observed, materially with the seasons of the year. Thus the descending Polar current, which appears so prevalent within the western half of the belt of waters referred to in the discussion of the whole of the voyages, is found to be of comparative small importance in the summer and autumn passages, whilst the Gulf-stream is then the most predominant. Hence the shifting of the upper margin of the Gulf-stream northward at these seasons, as popularly understood, obtains very decided confirmation.

In the results thus derived from the discussion of original observations on surface temperature of the North Atlantic, there will be found a general agreement with the conclusions of many other observers; but these now communicated, it is presumed, will be found of some importance as to the specific information yielded in respect of the belt of waters referred to. The indications, too, of a variety of effects from the meeting of contrary currents, are perhaps as conclusive as they are in some respects remarkable; for from the results now obtained, taken in connexion with a few auxiliary facts, we may safely infer the following varieties of operation derived from the meeting of the polar and tropical currents within the track discussed :

1. Strata Currents, consisting of a continuance of the respective currents after meeting in or near their original direction, by the overlaying of the denser waters from the North by the warm water of the Florida stream. Of this characteristic we have the most striking evidence in the observations of the Coast Survey of the United States, by intersections of the Gulf-stream. Thus in tracks across the stream having a general surface temperature of 80° to 82°, a depression of 10° to 15° was usually found at depths not exceeding 120 fathoms; of 20° to 25° at depths short of 500 fathoms; and in cases of 700 fathoms and upwards, a reduction sometimes of about 40° below the surface temperature! So that the existence of strata currents in this region of research-the Gulf-stream flowing above and the polar current below-seems to be unquestionable.

2. Interlacing Currents—where the polar and tropical currents on meeting seem to run past each other in repeated alternations of comparatively small breadth, in the manner of the fingers with the clasped hands-were strikingly shown in the rapid and great changes of the surface temperature within the fifth decimate section; and there is reason to believe that in these interlacings the edges of the respective waters flowed past each other with little intermingling, as if guided by walls in separate channels.

3. Deflected Currents-where currents on meeting from different but not exactly opposite quarters, as, for instance, from the S.W. and N.—are partially or mutually deflected into an easterly direction, so as to give rise to certain branches falling, as to one, on the southern coasts of Europe, and, as to the other, on the Norway and Spitzbergen shores. This species of mutual action in dense streams of water may find familiar illustration in places where the ebb-stream from a river falls into the tide-stream of the coast-the former pushing away the other, and each for a time. pursuing a separate deflected course, with but little apparent intermingling.

4. Passing Currents-where they run in parallel but opposite courses, and over separate ground—as in the distinctive Gulf-stream, in its general body, and the inshore polar current running within it over the St. George's and other American banks. Of the distinctiveness of the inshore polar current, Dr. Scoresby adduced this very striking evidence,-1st, that in observations on the temperature at the surface and bottom on the St. George's Bank made on one of his voyages, the surface temperature was, with trifling difference, maintained below: thus in latitude 40° 43', longitude 68° 35', the surface and the bottom, in 35 fathoms water, were both (May 22) at the temperature of 46°; and nearer the shore, in 69° 39′ W., when the surface was at 47°, the bottom in 39 fathoms was at 45°; and 2ndly, that the New England and New York pilots remark, in regard to an inshore current guided by the direction of the wind, that the current running south-westerly under a north-easterly gale is much stronger than the contrary current urged by a south-westerly gale.

In regard to the surface temperature and great currents of the Northern Ocean,

Dr. Scoresby could on this occasion only briefly touch. The discovery, in personal researches near the western coast of Spitzbergen, of comparatively warm water, increasing in warmth with the depth, he had long ago set forth, in the Account of the Arctic Regions,' as an indication of the extension of a branch of the Gulf-stream into the Icy Seas of Greenland; whilst the descent of a polar current, as indicated by the general set to the south-westward of the Greenland ices, had in the same work been amply proved and illustrated. This south-westerly drift from the east side of Greenland, associated with the southerly set out of Baffin's Bay, sufficiently explained both the cold surface temperature met with in the researches of the present paper, and the occurrence so prevalently of icebergs and drift ice in and near the meridians embraced by the banks of Newfoundland. And it might be reasonably inferred, perhaps, that both the position of these banks and the characteristic differences of the currents within the fifth and sixth decimate sections, so fully discussed, would have their true explanation in the consideration of the polar currents descending in two branches-the main one by the east coast of Newfoundland, the westerly and smaller one by the Strait of Belleisle.

Connected with this subject, it is very interesting to trace the economy and beneficial effects, as in many respects most obviously elicited, of the currents of the ocean. For here we find, as in all the Creator's works, the striking marks of benevolent design in the ordering and controling of the most subtle, or apparently vaguely acting agencies, to the benefit of the earth and its inhabitants. Of such indications may be noticed ::

1. The grand œconomy of oceanic currents in their equalizing tendency on the extreme temperatures of the different regions of the globe, from which the climate of the British Islands, for example, notwithstanding some minor disadvantages, derives such marked benefit in the diminishing of the range of temperature.

2. The maintaining, by the reciprocating currents, of the equable saltness of the ocean, and so preventing the differences in evaporation from the surface in the tropical and polar regions from destroying the characteristic quality of the salt sea. 3. The production by current eddies of sand-banks, favourable for the habitation of fishes, of which the banks of Newfoundland may be pointed to as characteristic examples.

4. The mingling of the waters of all regions of the globe, and the manuring, as it were, with fresh soil, of the great pastures of the creatures inhabiting the ocean.

5. The carrying away of large portions of the ice-formations of the higher latitudes for dissolution in a warmer climate, thus preventing the entire polar regions being filled with ice, and that ice being gradually pushed forward and maintained by its direct action on climate, which so might have rendered large portions of the now temperate zones uninhabitable or unsuitable for man.

6. And, in order to the due operation of counter and reciprocating currents betwixt the equatorial and polar regions, we must not overlook the economic design obvious in the distribution and configuration of the continents of the eastern and western hemispheres, betwixt which we find two great meridional channels permitting a free circulation of waters betwixt the two continents on opposite sides of the globe, and running, not improbably, from pole to pole!

On Deep-Sea Soundings and Errors therein from Strata-Currents, with Suggestions for their investigation. By the Rev. W. SCORESBY, D.D.,

F.R.S., Corresp. Institute of France, &c.

No long time has elapsed since the notion was very prevalent among seamen, that it was impossible to sound the ocean beyond the depth of a very few hundreds of fathoms. It was imagined that in water exerting a superincumbent pressure on the plummet greater than the weight of metal, no sounding-lead would sink; a curious notion, which could not have been otherwise than a delusion, unless the water of the sea had been indefinitely compressible, so as to have become of equal density, at least, with that of the metal of the plummet.

There is a difficulty, however, though of a very different nature from that just noticed, in respect to the obtaining of correct information in very deep soundings, which seems, from the confidence given to recent experiments, to have been