ARTICLE II.

FIRST DIVISION, SECTION 2.

HYDROGRAPHY.

By the late REAR-ADMIRAL F. W. BEECHEY, R.N.
(Revised by Captain Washington, R.N.)

Making a Passage.

THE observer's attention is directed first to those objects which affect the passage of a vessel from one part of the globe to another; such as the movement, the duration, the limits, and the periodic occurrences of those great currents of the atmosphere and of the ocean, upon which the speedy and successful issue of a passage mainly depends.

Well recorded and established facts bearing upon the several points connected with these inquiries are highly important to navigation, and may be collected by every assiduous seaman in the ordinary course of his duties.

1. It is well known that in various parts of the globe there exist monsoons, and zones of trade and variable winds; and that these and other disturbances of the atmosphere which influence the surface of the ocean are the principal causes of the many currents which sweep over the face of the earth. The effect of these upon a vessel passing to and fro is one of the most useful inquiries a seaman can make; and as both (wind and current) perform an important part in the economy of nature, an additional interest attaches to a correct knowledge of them. The seaman should therefore not only carefully note the direction and force of the winds, but should connect with such entries notices as to when and where any continued or periodic

wind commenced and terminated; what was its strength and effect upon the passage; whether it came on suddenly, and was furious while it lasted, or otherwise; whether it was preceded by any particular symptoms, and whether it was such as usually occurs at that season; and lastly, whether it be advisable to cross this wind in any particular direction, such as close hauled or large, &c.

2. To detect the current, a more than ordinary attention must be paid to the reckoning of the ship: the compass by which the course is steered should frequently be compared with that by which the variation is determined, in every position of the ship's head;* and the ship's place should be determined by observation at least once a day. Sights for chronometer morning and evening should both be referred to noon, at which time the latitude will of course be observed; and all observations for latitude at night, or for fixing the ship's place at any time, should be referred to one period of the day, in order that the position of the ship by observation, as compared with her place by the Dead Reckoning, may give the direction and force of the current, if any, for the twenty-four hours. These observations should all be entered in a table; and at the close of certain obvious and natural periods of a passage, such as that of entering or emerging from the trade-wind, the calm latitudes, the commencement or termination of the monsoon, of any positive change of current, or from any continued state of things to another, the whole effect of the current for the period should be deduced, and an average of its daily rate and set be given, together with any remarks which may be considered useful.

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3. With the direction of the current thus determined, it very desirable to connect the temperature of the surface of the sea, for it has been by such observations that we have been able to trace, with a certainty amounting almost to proof, the continuous course of the same body of water for thousands of miles over the troubled surface of the

*See Article IV., Terrestrial Magnetism.'

ocean, and that other curious and important facts in physical hydrography have been ascertained. We would therefore urge attention to the subject as one of considerable importance to navigation. As a proof of its influence upon a passage, we need only instance the remarkable phenomenon of the Equatorial and Guinea currents: two streams in contact, but flowing in opposite directions, and having a temperature differing 10 or 12 degrees from each other, and yet pursuing their opposite courses for upwards of a thousand miles; and according as a vessel is placed in one or the other of these currents, will her progress be aided or retarded from 40 to 50 miles a day.*

Could we but obtain a register of the temperature of the surface of the sea from every ship in active service, we should be able in a short time to construct tables showing the normal temperature of the surface of the ocean for every 5° of latitude for every month in the year, and a comparison of these with the actual temperature of the surface at any particular spot, and in any particular month, would at once manifest an abnormal difference, if any existed, and lead to a knowledge of its cause, which might prove of considerable use to the mariner by acquainting him with the movement of the great body of water in which he was sailing; either retarding or accelerating his progress, as the case might be, and at all events affecting his reckoning. Or it might lead to a closer determination of the limits and periodical changes of currents which, as before observed, are everywhere running over the surface of the sea as rivers run over dry land.†

It is therefore recommended to add to the table of currents a column for the temperature of the open air, and another for that of the surface of the sea, which should be registered frequently during the twenty-four hours; but as such observations form an essential feature in the meteorological register of a voyage, they should be made at

Sabine's Hydrographical Notices.'

+ Such registration is now in progress, and the resulting facts are collected at the Meteorological Department of the Board of Trade. (W.)

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the times and in the manner indicated under the head of Meteorology.*

4. There should also be noted in the Remark column the occurrence of masses of seaweed, or of any continued appearance even of small patches of this or of any other floating substances which may be seen; and if opportunity offers, deep-sea soundings should be tried at the spot. "It were much to be wished," says Humboldt, Personal Narrative, vol. ii. p. 11, "that navigators heaved the lead more frequently in these latitudes covered with weeds, for it is asserted that Dutch pilots have found a series of shoals extending from the banks of Newfoundland to the coast of Scotland by using lines composed of silk thread."+ Flocks of birds should also be noted. In many places, the Pacific especially, the tern are useful monitors of an approach to those low specks of coral which endanger the path of the navigator through the labyrinth of the great South Sea. In short, everything that may seem to the voyager to be interesting or new, or likely to be useful, should find a place in the Remark column.

At the end of the passage a summary of these remarks should be given, the whole effect of the current for each particular portion of the passage recapitulated, such as that which was due to the N.E. or S.E. trade-wind, or to the monsoon, as the case might be, and distinguishing each;

If passing Cape Horn, or through seas where icebergs may be moving about, these observations cannot be made too frequently in thick weather, especially as a precaution, for the water appears to be influenced to a considerable distance around these masses, particularly in their wake.

A printed registry, termed a Weather Book, with full instructions for observing, is now supplied to all H. M. ships, and to many merchant vessels. This register is called by the American navigators an “Abstract Log."

In a continuous line of soundings across the Atlantic, between Ireland and Newfoundland, in June 1857, preparatory to laying the telegraph cable, Commander Dayman found a depth of 2400 fathoms, and not the slightest indication of any shoal. But farther northward there may be shallower water. (W.)