altogether overlooked. To this difficulty, and the errors likely to be produced thereby on the determination of depths, it was one of the objects of the author of this communication to elucidate and establish.

He did not refer, however, to cases where the depths were not very profound, or where the time occupied by the descent of the plummet was inconsiderable; for he, Dr. Scoresby, had frequently reached depths of near a mile, or even more than a mile, in the Greenland Seas-at a period when such soundings were novel or unprecedented-with results, owing to peculiar and favouring circumstances, he believed, perfectly satisfactory. But far otherwise than satisfactory, as he expected to be able to show, must be some of those extraordinary soundings of recent years, in which depths of five, six, or nearly eight miles were supposed to be established.

If the sea were a stationary body, or if its currents were uniform movements of the entire mass of waters from the surface to the bottom, then the plummet might be fairly expected to take a direct and perpendicular course downward, so that the length of line run out would be the accurate measure of the depth sounded. But if in the place or region of sounding, strata-currents, so prevalent in the Main Ocean, should be running in different directions; or, what would have the same effect, if one stratum of water, say a superficial stratum, should be at motion and the main body below at rest, no correct results could be derived from the experiments referred to, where the time occupied in the running out of the line extended, in some of the more interesting cases, to many hours.

Under such circumstances, during the passage of the plummet through strata

currents, the line, it must be obvious, would be carried away in its different portions by the movements of the water, for which the tendency to assume a perpendicular position below the point of surface-suspension could afford no adequate corrective. Thus suppose the surface-stratum, W, to be running westerly, and the lower stratum, E, easterly (or at rest) with a difference of velocity of two miles an hour. The descent through the first portion, where the vessel would participate in the action of the current, might be quite perpendicular; but on the entering of the plummet into the lower stratum, the lead and line would be carried, or, in relation to the surface position, appear to be carried eastward, at the rate of two miles in the hour. Hence in the case of the experiments of Captain Denham, where the descent in the last four miles required above an hour and a half of time per mile, the plummet might be carried some miles away from the perpendicular, so as to occasion a very large error in the depth apparently determined. In respect to Captain Denham's deep-sea soundings, indeed, the error assumed is but conjectural, depending on the circumstance of the actual existence in the place of experimentlatitude 36° 49' S., longitude 37° 6' W.-of strata-currents. But in some of the deep soundings attempted in the Gulf-stream, where, in the difference of the temperature above and below (some 46°), we have conclusive evidence of stratacurrents, the determinations must, it is to be believed, have been more or less inaccurate, probably greatly erroneous.

In regard to the proportion of error-being without data both as to the flow of the different currents, and the measure of resistance, under the circumstances, afforded by the water to the attainment of a perpendicular position by the plummet no satisfactory estimate can be offered; but that a considerable resistance would be presented against the corrective tendency of the plummet, so that the line, however

thin, would be greatly carried away, evidence from analogous facts may be satisfactorily adduced.

Thus, the manner in which the deep-sea lead is carried away, and the determinations rendered uncertain, when soundings are attempted in depths only of 50 to 100 fathoms, from a ship having but very little headway, might alone justify the asserted grounds of probable error on the deep-sea soundings referred to.

But further evidence of resistance in water, against the assuming of a straight position of a rope or line, under tension, where it may have been previously thrown into a curve, may be derived from some striking facts in the author's personal experience whilst engaged in the Northern Whale Fishery. Let the annead diagram be supposed to represent one of these characteristic cases, where a boat is seen with its bow in contact with a large field of ice.

A whale, it is assumed, has been harpooned from this boat, which, as in such circumstances generally happens, retreats for shelter beneath the ice-field, drawing out the line with great force after it. Having pursued its original course beneath for a distance probably of a mile, the necessity for respiration induces its return. Its probable course may be shown by the line in the diagram, one end of it being attached to the boat, and the other, by means of a harpoon, to the whale here represented as having risen to the surface astern of the fast-boat. A few minutes previous, perhaps, to the reappearance of the whale, the line attached to the boat, which might have been for some time in a state of quiet or unaltered tension, is, by a second effort of the entangled animal, powerfully withdrawn, so that the boat may be pressed against the ice, as at first, with a force, possibly, equivalent to that of a ton weight! Yet, in this case, whilst the direction of the action on the boat is ahead, say, northward, the actual place of the whale exerting this singular energy, may be astern, or southward, the resistance of the water on the line preventing its taking a straight direction, and causing it to sweep round a body of water in a circuit, something after the manner of resistance of a more solid material.

Observing this curious fact whilst he, the author of the communication, in very early life occupied the station of harpooner in the Greenland Fishery, he successfully availed himself of it for facilitating the capture of whales which might have been "struck" by any of his associates. In the case of a whale being harpooned in "clear water," where the " fast-boat," unencumbered by ice, was free to follow the course of the entangled animal, the practice of the other pursuers, as they might successively come up to assist in the capture, was ordinarily to distribute themselves in different angles in considerable advance of the fast-boat. But he, noting carefully the cessation of the advance of the original boat, which often happened, or its gradual deviation from the course at first pursued, was accustomed to take up a position either astern of the fast-boat, or wide upon its beam on the side towards which the deviation tended, calculating that the resistance of the line by the water would cause the direction of the boat's deviation to lag far behind that of the whale. The result was so satisfactory, that in a large majority of cases, where the rule applied, his boat was found so near the wounded animal on its reappearance at the surface, that he was most frequently successful in striking the second harpoon.

Hence, under such variety of illustration applicable to the case of deep-sea soundings in the regions of strata-currents, it appeared to be an inevitable result,

that the sounding-line in these attempts must be so carried away with the moving strata of waters as to render the length of line run out a very imperfect indication of the depth reached by the plummet.

Dr. Scoresby next proceeded to communicate his plan for the determination of surface-currents, and relatively of strata-currents.

The ordinary mode of determining the set and velocity of currents-by the differences betwixt a ship's position on each day's run as determined by celestial observations and the "dead-reckoning"-is necessarily and obviously very uncertain, often entirely delusive. None of the elements of the log and reckoning are or can be correct; the distance run, the compass course, the steerage of the ship, are all more or less inaccurate. The author's own experience had afforded numerous cases in practical navigation of great and remarkable differences betwixt the day'sreckoning and celestial observations, such as might have been taken as indications of currents of considerable influence, where, it was almost certain, the main differences were really due to bad steering (when scudding or sailing with the wind on the beam or quarter); to errors in the distances indicated by the log, or to peculiarities or changes in the ship's local attraction.

No doubt broad determinations as to great and decided currents, and proximate results by means of multiplied observations on currents of moderate velocities, are derivable from the ordinary process; but for really satisfactory results, far more accurate and conclusive processes need to be instituted. And it would be well deserving of an enlightened government of a maritime country like ours to employ some of their smaller war-vessels, and so to afford useful and instructive practice to junior officers, in investigations concerning currents, and particularly strataAnd for such investigations certain modes, Dr. Scoresby believed, might be made easily available, calculated to yield much valuable and interesting information on this important subject.

currents.

Two leading processes were then described as appearing to be applicable to these determinations :

1. The planting in particular positions in the ocean, from an attendant vessel, buoys with flags, kept in their places by a resisting apparatus below the surface, which may be denominated a current-measurer, and determining, after a night's interval, for instance, the changes of their position from celestial observations. A convenient construction of the current-measurer, with a view to portability of stowage, might be a double oblong frame of iron, attached by a transverse pin as a hinge, by the middle of each, so as to allow of their being spread out as vanes in a vertical plane, or placed flat on each other when not in use. These frames, which might be 6 or 8 feet in length by 2 or 3 in breadth, being covered with linen, would, when sunk in the water, as indicated by the annexed figure, afford sufficient resistance, probably, for all the purposes contemplated.

2. Placing, during a calm, a small boat in the water, constructed for the purpose, light, and slightly resisting of motion, with the current apparatus for the determination of the relative set of strata-currents.-The current-measurer, attached and suspended by a small wire run off a reel fixed in the bow of the boat, might be let down to various depths in succession, with a register-thermometer attached at each new depth, when the motion of the boat and its direction, as shown by the position of a surfacefloat or buoy, would, after but short intervals of time, indicate, proximately, the relative motions of the surfacewater and the water at the several depths of the resisting apparatus below; whilst the register-thermometers might give useful information on the extremes of temperature of the various sections of water passed through.

By these arrangements information would be obtained as to the following particulars :

-

By the surface-buoy (1) we should ascertain, if the weather were sufficiently calm,

the motion of the surface-water; by the movements of the boat, (2) the relative motions of the surface-water, and that at the depth of the current-measurer, at the first trial; an indication of the changes at other depths; and, on reeling in the wire, the highest and lowest temperature would be shown at each of the depths examined (that is, when the changes were in one way, as from warm to cold), and thus the several results might be compared with the surface-temperature taken at the commencement, and at each change of depth.

The cases in which such experiments would be the most interesting, would probably be found in places of the ocean where great differences of temperature are met with at comparatively moderate differences of depth. In some of the positions examined, for instance, by the officers of the United States Coast Survey, the temperature was found to sink, from about 80° at the surface, sometimes to 70°, or even 65°, in depths not exceeding 120 fathoms, and down to 64o or 63° (near 20° lower than at the surface), in depths of 120 ranging to 480 fathoms; whilst a temperature as low as 44°, or less, was met with at the depth of about 700 fathoms. Now, in such cases-cases prevailing extensively within and about the edges of the Gulfstream, or within the changes of surface-temperature in the transatlantic passagewe should probably obtain by the processes described results of no ordinary interest and importance.

The results, it must be admitted, could only be proximate; for the boat, moved by the deeply-sunk current-measurer, it is obvious could not follow vertically above it; but under the action of an obliquely ranging wire, when both boat and wire must present a force of resistance, the boat must take a position behind. Yet, if the current differences were considerable in velocity and direction, perhaps experiments continued for a few hours at a time, and repeated under a due variety of circumstances, might afford data for mathematical determinations of resistance and corrections. And, in certain cases, in regions where the great oceanic currents overlay one another, like those from the Polar Seas and the Tropics, conclusions abundantly satisfactory might, no doubt, be realized.

METEOROLOGY.

On a proposed Barometric Pendulum, for the Registration of the Mean Atmospheric Pressure during long Periods of Time. By W. J. MACQUORN RANKINE, C.E., F.R.S.S. Lond. and Edinb.

The author proposes to use the variations of the rate of a clock to determine the mean barometric pressure during long periods.

For this purpose the clock should be regulated by a centrifugal or revolving pendulum, part of which should consist of a siphon barometer. The rising and falling of the mercury would affect the rate of the clock; so that from the number of revolutions of the pendulum in a given time might be deduced approximately the mean height of the mercurial column during that period.

The author investigates the formula to be used for this purpose, and points out the nature and mode of determination of the corrections required for temperature, obliquity of the barometer, and centrifugal force, and also for the difference between the square root of the mean of the squares of the barometric heights, which is the quantity ascertained in the first instance, and the mean of the heights, which is the quantity sought.

On a Concentric Iris, as seen from the ridge of Snowdon, near the summit, on the morning of the 13th of June 1853, about an hour after sunrise, projected upon the clouds floating along the sides of the Mountain. By WILLIAM GRAY, Jun

The iris continued in sight about an hour, becoming gradually depressed into the shadow thrown by the mountain on the clouds.

When first seen the colours were exceedingly brilliant, and exhibited four concen

tric ranges of the prismatic colours nearly perfect, ranging from violet in the centre to a fourth circle of violet forming the outermost distinct circumference; faint indications of a fourth circle of red were occasionally visible beyond it.

The Irish Sea seen in the distance.

On the Meteorology of Hull. By WILLIAM LAWTON.

After describing the instruments used and their situation with regard to the town and surrounding objects, the author referred to the observations themselves, which consist of three separate series. 1st. The observations on temperature of Dr. Fielding, late of Hull, extending from 1831 to 1836 (hoth inclusive), left in the form of a chart. These have been reduced to their numerical value and placed in a tabulated form. 2nd. Mr. Lawton's observations of a general character, commencing with January 1849, and still continued. 3rd. The Literary and Philosophical Society's observations, commencing with 1851, and also continued.

The following table headed Atmospheric Pressure, represents the mean barometrical observations for each month and for the year. The first three columns are the results of the author's observations taken daily at 9 A.M. and 6 P.M. The first column represents the average highest monthly maxima for the years 1849, 1850, 1851 and 1852; the second column the average lowest monthly minima; and the third column the mean monthly height for the same period.

The fourth and fifth columns give the highest and lowest readings for each month from the Philosophical Society's Register, and the sixth column of the same table the mean of each month for the year 1851, which closely coincide with Mr. Lawton's observations for the same period. The mean height of the barometer for December of that year was the greatest yet registered, being 30-34; the Philosophical Society's 30.264. By a reference to the third column containing the mean height on the average of four years from 1849 to 1852, it will be perceived the readings are the highest in February, March and September, and lowest in January, October and November.

The mean heights of each of the four years observed have not varied above '05 of an inch.

To this table are added the results of four years' observations made at Wakefield by W. R. Milner, Esq., Surgeon, during the same period, and kindly furnished by that gentleman.

Bearing in mind the daily fluctuations or tides of the barometer, which it is stated by Professor Phillips rise at York twice to maxima, about 9 or 10 A.M. and P.M.,