THE

NAUTICAL MAGAZINE

AND

Naval Chronicle.

NOVEMBER, 1862.

ORT ON THE DEEP SEA SOUNDINGS TO THE WESTWARD OF IRELAND, made in H M.S." Porcupine," in June, July, and August, 1862.

Belfast, September 30th, 1862. -The Atlantic Submarine Telegraph Company having requested ords Commissioners of the Admiralty to have some deep soundaken off the western coast of Ireland, principally to ascertain er the apparent sudden dip in the soundings from 550 to 1,750 ms, found by Commander Dayman in the year 1857, in the paof 52° 15′ N., extends further North or South, and to endeavour ek out a more gradual slope into the bed of the ocean, their hips were pleased to direct that the Porcupine, then fitting at nport for the survey of the North Sea, should be despatched on service.

e Porcupine is a paddle steamer of 130 horse power and 380 She was manned by a crew of forty-nine officers and men, and tted with a donkey engine for heaving in the line; also with ight iron reels, three large for the deep sea line, and two small d line, capable of holding 2,000 fathoms of line each. From reels the line was run off when sounding, and reeled on them nd, as it was hove in by the donkey engine. The Porcupine lso supplied at Devonport with 10,000 fathoms of the ordinary sea line and 13,000 fathoms of cod line, made expressly for deep unding, with an ample supply of sinkers and weights, and the og and other apparatus for bringing up the bottom; Johnson's

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and Hearder's pressure gauges to show the depth were also supplied, as well as metallic and ordinary deep sea thermometers to test the temperature. At Galway a further supply of 10,000 fathoms of Messrs. Newall's cod line was received on board, besides 11,500 fathoms of a smaller and less expensive line. The weight per 1,000 fathoms, with the breaking strain of these sounding lines, was as follows:

The lines were marked in the usual way, viz., blue at 50 fathoms, white at 100 fathoms, and red at 1,000 fathoms.

The soundings were always taken from the bow of the vessel. With the main and mizen sheets out we had no difficulty in keeping her head to wind; and an occasional easy turn ahead sufficed to keep her bow directly over the descending lead.

The principle of using a small line and heavy weight for obtaining the depth was that adopted. I believe it to be the only means at present known for obtaining the true depth.

When using a heavy line, such as the ordinary deep sea line, the difference of interval after the weight strikes the bottom is not sufficiently marked to enable one to say confidently when it is down, particularly should there be any sea, and none of the instruments we were supplied with, whether of a rotatory character, like Walker's, or those depending on compression, as Johnson's and Hearder's pressure guages, give any results that can be at all relied on.

The cod line supplied by Messrs. Newall, of Gateshead, is an admirable line for this purpose. The weight was sometimes brought up by it from great depths. On one occasion it raised a 64 lb. weight from a depth of 1750 fathoms; but as the whole quantity out is frequently sacrificed at each sounding, the expence becomes a serious consideration when the soundings are required near each other; and I found the lighter and much less expensive lines answer equally well in smooth water, where the depth of water alone was required.

The strongest line we had for bringing up a specimen of the bottom, with the instruments for testing the temperature and pressure, was the ordinery deep sea line. If, as it sometimes happens, the weight does not detach itself, this line would prove unequal to the strain, and at some sudden heave of the sea would break away, losing all our instruments.

The simplicity, cheapness, and certainty of action of the cup lead,

of from 56 lbs. to 75 lbs. weight, renders it an invaluable instrument in depths under a thousand fathoms, bringing up a good wine glass ful of the bottom at each cast. It may be used either with the cod or ordinary deep sea line. In greater depths when a specimen of the bottom was required, we used the Bulldog machine.

To save time, the two operations of determining the depth by a small line, and sending down the instruments for scientific purposes, were carried out together, an officer being stationed at each line to time the marks in their passage over the gunwale. A deep sounding, when the instruments were to be recovered, would occupy from two to four hours.

Having made these preliminary observations, I may now proceed with the progress of the voyage.

Having swung ship for compass deviation, I sailed from Plymouth Sound on the 22nd of June, and on the 24th commenced our examinations, in pursuance of your orders, at the 100 fathoms line on the 51st parallel of latitude. The deep water valley crossed by Commander Dayman ninety miles west of Valentia, was found to extend to this parallel, as we had 1,180 fathoms in its deepest part and 375 fathoms on the bank outside it. From the depth of 1000 fathoms in this depression, the Bulldog machine brought up a bivalve shell embedded in the soft clay.

On crossing the bank to the westward, we passed from a depth of 710 fathoms to 1,550 fathoms in a distance of seven miles. Although this increase of depth seems so great, if the incline is gradual, of which we have no evidence to the contrary, it amounts to but 12 feet of dip in 100 feet horizontal, or about 1 in 8.

To the westward of this we dropped our lead on the position of a reported vigia (the Brazil Rock) and obtained 2,350 fathoms, and here the deep sea line being unequal to the strain broke, taking with it all our instruments attached.

With reference to this and other vigias in this part of the ocean, I may observe that we frequently passed balks of timber, covered with barnacles and sea weed, having somewhat the appearance of a rock awash.

Carrying out the system of sounding laid down for me in your orders in the parallel of 51° 35', we passed from 1,440 to 930 fathoms in a distance of 2.7 miles, or a little under 19 feet of dip to 100 feet horizontal, and this is the steepest incline we have met with.

The unsettled weather we experienced frequently interrupted our work, and on the 8th of July, having expended our coals, I ran into Galway to replenish, and obtain a fresh rate for our chronometers. We were detained here by continual gales until the 21st, when the weather moderating we again sailed, carrying out a line of soundings with us; but had scarcely arrived on our ground, when the weather became more severe than ever, and on the morning of the 24th, while lying to in a heavy gale, we had the misfortune to twist our rudderhead off. This compelled us to return to Galway for repairs, and in