To one end of a stout spar, A C, was firmly lashed a block, D, and to one end of the rope which passed through this block was attached a smaller block, G, which allowed the dredge-rope

E

A

H

or sounding-line, I G H, to run easily through it. The other end of the rope through D was made fast to the "accumulator," E F, which consisted of a number of solid vulcanised indiarubber springs, about two feet long, connected at each end to a disc of wood. In the event of the dredge fouling among rocks, or the vessel pitching much in a sea, a sudden strain was put upon the dredge-rope and on the block G, and thence communicated by the rope G D F to the accumulator, E F, which immediately was stretched out, sometimes to three times its original length. On the only occasion when a dredge was lost, the writer saw a strain upon the indicator amounting

to 17 cwt. a few minutes before the dredge-rope parted. This happened in comparatively shallow water, on a day when what a landsman would call half a gale of wind was blowing.

The expedition was divided into three cruises; the first, under the charge of Mr. J. Gwyn Jeffreys, F.R.S., and accompanied by the writer, lasted from the end of May till the middle of July, and the area of its work lay between latitudes 51° 20' N., and 57° 30′ N. (Rockall), the westernmost point being 15° 30′ W. The second, under the charge of Dr. Wyville Thomson, F.R.S., accompanied by Mr. John Hunter, M.A., of Belfast, lasted from the end of July to the middle of August, and was occupied in explorations off the S.W. of Ireland; the deepest dredging of all, 2,435 fathoms, being accomplished at the most southerly point reached, 47° 35′ N. and 12° 15′ E. The third, under the charge of Dr. Carpenter, F.R.S., accompanied by Dr. Wyville Thomson and Mr. P. H. Carpenter, lasted from the middle of August to early in September, and was devoted to an examination of the "warm and cold areas" between the Hebrides, Shetlands, and Faröes, the northern limit being Thorshaven, in the Faröes, the western 9° 20′ W., and the eastern 0° 35′ E. In this cruise the greatest depth attained was 750 fathoms, but during it a most important addition to the dredging apparatus was made by Capt. Calver. It consisted of horizontal arms attached to the dredge frame, to which were fastened two or three "swabs," or "hempen tangles" as they were christened by their inventor, by which the bottom of the sea was swept as well as scraped. In this way many animals were captured which seldom or never were obtained in the dredge-bag, and the utility of this contrivance was so evident that no deep-sea dredge can henceforth be considered complete without it.

In order to dredge in any particular spot, it is necessary to know the exact depth of water. Sounding, therefore, is an essential preliminary to dredging. In the Porcupine's soundings three objects were attained- (1) a knowledge of the exact depth, (2) the temperature at that depth, (3) a sample of water from the bottom. Where there was reason to believe that the depth was less than 1,000 fathoms, an ordinary "deepsea cup-lead," weighing 1 cwt., was used; in other cases the "Hydra" machine before described. The sinker or weight having been attached, two of the Miller-Casella thermometers were made fast to the line immediately above the weight, and close to them the water-bottle. The whole was then let go, the line running out with great rapidity, at the rate of 100 fathoms per minute at first. By a seconds' watch, the time of each 100 fathoms in running out was noticed, the interval increasing with the friction of the water on the greater length of

1

line, so that towards the end of a 1,200 or 1,300 fathoms' sounding between two and three minutes were required for 100 fathoms to run out. Capt. Calver took each sounding with his own hands, and was able to tell with great certainty the precise moment when the weight struck the ground. In the fine weather with which we were usually favoured, the soundingline even at these great depths hung quite vertically over the stern of the vessel, and the bottom could be felt at the end of it, by slightly raising and lowering the line by hand. Five minutes were then allowed for the thermometers to take up the temperature of the surrounding water, after which the line was hove-in by the donkey-engine, and when the instruments arrived at the surface the indices of the thermometers were read and the results recorded. Soundings were taken in this manner at ninety different stations, and when it was desired to take the temperature of the sea, and samples of water at various vertical depths (short of the bottom) over the same spot, the operation was repeated with the cup-lead, letting it down, e.g., to 1,250, 1,000, 750, 500, and 250 fathoms, and drawing it up again after each operation. In this way the serial temperature soundings were obtained.

The contents of the water-bottle were immediately examined for their specific gravity by delicate glass hydrometers reading to four decimal places; for the organic matter contained in them by the chameleon (permanganate of potash) test; and for the quantity and relative proportions of gases dissolved in it. This last point was determined by Dr. W. A. Miller's apparatus, which was first adapted to the necessities of shipboard by the writer. The gases were expelled from the water by boiling it in such a way that no air had access to it, and were collected over mercury and measured. The carbonic acid was then absorbed by potash, and the oxygen by pyrogallic acid; the remainder being taken as nitrogen. In addition to being thus tested, some of the contents of the water-bottle were preserved for further analysis on shore.

It now remains to describe the process of deep-sea dredging proper. In water less than 500 fathoms' depth, two dredges were frequently employed, one from the bow, another from the stern; but at greater depths only one dredge was used. The object to be attained was to get the dredge to fall vertically through the water to its right position on the bottom, over which it was to be dragged by the motion of the vessel at the surface. In small depths this was a matter of little difficulty, as the time occupied by the dredge in falling to the bottom was so short that the vessel did not drift much from one spot, and then, if the drift of the vessel was not enough, recourse was had to the paddles to move the dredge over the ground.