that which occurred in the calm latitudes or during a period of variable winds, or otherwise, averaging the daily rate; and then might follow any remarks you may wish to make either upon them or upon any other feature of the passage; together with any directions or hints which might be considered useful to those who should follow over the same ground; such as whether any advantage would have been gained by steering more to the east or west, or in any other direction; whether any time would have been saved by making the land on any other bearing than that in which. you hit upon it; and in short any remarks which would be instrumental in conveying to others information which you would have wished to possess yourself at the outset of the

passage.

Currents.

5. It is very desirable that observations upon the course of the waters of the ocean should be made without intermission; and that a continued register of the temperature of the surface, and occasionally of its submerged strata,* should be kept, as it is only by numerous well-recorded observations of this nature that we shall ever be able satisfactorily to define the limits of the various zones of moving water which sweep over the face of the globe, mingling the waters of the Polar Seas with those of the equatorial regions, and even affecting the climate of extensive districts. But if from various causes a connected series cannot be continued throughout these great currents, at least an endeavour should be made to commence a register on approaching the limits of such as are now approximately defined, and to continue it while any interest appears to attach to the subject: such as that of the Gulf-stream; the Trade-wind drift; the Guinea and Equatorial current; the

By means of self-registering thermometers, properly set and carefully lowered and as carefully hauled in (without jerks).

+ See Humboldt on the Climate of Peru; Sabine on the Climate of St. Thomas Island, &c.; Maury on the Physical Geography of the Sea.

Cape of Good Hope current, blending with the southeast trade drift; and the Brazil current, in the Atlantic; with the Mozambique and Agulhas current; the Trade drift, and monsoon current of the Arabian and Bengal gulfs, in the Indian Ocean. Also the remarkable Peruvian current sweeping along the western coast of South America; the Trade drift, and Equatorial current; the Mexican current, passing along from Panamá to the Gulf of California, according to the monsoon; the countercurrents north and south of these, and the moving belt along the coast of Japan and Korea to Kamtchatka, in the great Pacific Ocean. And particularly noting, as of great importance to navigation, the limits of the outer currents around the Cape of Good Hope and Cape Horn, all of which will be found on a small scale delineated in a general chart at the end of this paper. (Plate B.)

Some of these currents maintain a constant difference of several degrees between their own temperature and that of the mean state of the water about them, and all observations which can throw light upon this subject, and upon the limits, course, and velocity of the stream, will be most acceptable.

6. In passing through any of these great currents, the observer should carefully define the extent of the belt of moving water at the parallel in which he crossed it; the limit of the eddy on either side of it; determine the rate and set of both; carefully note every barometrical or thermometrical change of the air, or alteration in the temperature or specific gravity of the sea, and if possible the depths to which these temperatures extend; and record all appearances and changes which may appear of interest or seem to be useful to those who may follow over the same ground.

To detect the motion of the stream the remarks in (2) should be attended to, with the exception that here the position of the ship should be frequently ascertained during the day by astronomical observation, and the course and rate of the current deduced for short intervals of time instead

of for the twenty-four hours. The observations should commence previous to entering the body of moving water, and be continued until after the vessel has quitted it, when it will be advisable to occupy a page of the journal with a graphic delineation of the several courses of the stream, indicated by arrows, and of the several stages of the vessel's progress by the various temperatures which have been observed, noting the places where ripples were seen, or where drift-wood, seaweed, or other floating substances occurred.

The Stream or Surface Drift.

7. Currents have been spoken of under the head of "making a passage," as they affect a ship's route across the ocean, and may have been determined by the position of the ship by Dead reckoning differing from that by observation. But it will be proper further to try the set of the surface of the water on all favourable occasions, by the ordinary method of anchoring, or of sinking a weight, endeavouring if possible to get observations on the same day at about six hours apart, in order that it may be seen whether the stream be due to a tide or not. If the ship be in soundings, and the day be calm, a very simple way of effecting this without the trouble of either anchoring or lowering a boat,* is to drop a heavy lead from the quarter, and, after it has reached the bottom, to run out a small quantity of stray line, and then make fast the "nipper," or a billet of wood, to the line; and at the same time to fasten the end of the log line to it, and veer away both together. Then mark by a watch the time each knot is in running out, buoying up the line by a chip of wood; when all the line has run out, take the bearing of the nipper by a compass, and haul all in together. If currents be tried

* An objection to trying the current in a boat is the uncertainty of the compass, unless Dent's spirit-compass be used, which is strongly recommended.

+ If the lead-line be not hitched to the nipper, the tide may drag the line through it, and there will be no result.

when there are no soundings, the result is merely the relative motions of the upper and lower strata of the water, and it would be difficult to say which way either were going; but if we can possibly determine by astronomical observations the course of the upper surface, we shall thence be able to deduce the set of the lower; and if there be found any difference of moment, it will be very desirable to ascertain the temperature of both upper and lower strata of the water, and to record them with the other observations. These observations ought always to be made on 'calm days, and the greater the depth to which the weight be sunk the better. Bottles thrown overboard with a label inside, containing the date and latitude and longitude of the spot where cast into the sea, afford ready means of detecting the current if picked up afterwards, and ships would do well frequently to expend a few empty bottles in this way.* In the event of meeting any such drifting at sea, they should be picked up, their contents copied, and the date and position of the spot added to the label; they should then be carefully resealed and returned to the ocean, and a copy of the label forwarded to the Admiralty.

8. If near to any shore, a few points of which are well fixed, and the water be found too deep for anchorage, the course of the stream may still be ascertained by noting the drift of a float-a plank, for instance, weighted at one end, so that the other just floats above the surface; or a weighted breaker (bareca)-fixing its position from time to time by angles taken in a boat at the several places, and noting the intervals by a watch.

Such methods may, of course, be resorted to when circumstances do not admit of greater accuracy; but whenever it can be done, the course and rate of the stream should be observed every hour during both tides, and the times of slack water carefully noted, by anchoring a boat or vessel. Upon an open coast one set of such observations, made here and

*The bottles, before being sealed, should be ballasted with a little dry sand, consolidated at the bottom with bees'-wax or pitch run in, that the bottle may be kept upright, and not swim too light.

there, well clear of the headlands, will be sufficient; but in channels and straits, in which the tide enters at both extremities, the tidal phenomena are so varied and full of interest, that it becomes highly important to spread the observations over as large an extent of the channel as possible, and to pursue a regular system of hourly observation throughout both the ingoing and outgoing streams.

It is desirable to know at each place the time of slack water, the direction in which the stream turns, and the rate and course at which it runs during its several stages. The stations should be numbered, and the times all referred to one meridian. In such channels there will probably be one or more places where the streams meet, and there, of course, observations will be made; and as one of these places will probably be the virtual head of the tide wave, it may so happen that the time of the high and low water there by the shore will govern the turn of the stream either along the whole channel or until it reaches a spot where another meeting of the streams occurs. In such a channel also it will probably be found (as in the Irish Channel) that the same stream makes high water at one end and low water at the other at the same time; so that the observer must entirely divest his mind of the too often mistaken notion of the turn of the stream being governed by the rise and fall of the water in its immediate locality. As our space does not admit of further detail, I shall leave the subject in the hands of the observer with a remark which, whilst it will put him in possession of what kind of observations are required, will at the same time, I think, insure his interest in the subject and his hearty desire to co-operate in the matter.

In the Philosophical Transactions, 1848, Part I.,* it has been shown that in such a channel as that above mentioned there have been discovered two remarkable spots, in one of which the stream runs with considerable velocity without

This valuable paper, by the late Rear-Admiral Beechey, as well as another on the Tides of the Channel and North Sea, is annexed to the Tide Tables published annually by the Admiralty, and supplied to all H. M. ships. (W.)