ART. VI.-On the importance of more frequent and more accurate Deep-sea Soundings in connection with the successful establishment of a Submarine Telegraph across the Atlantic; by Prof. W. P. TROWBRIDGE, Assistant U. S. Coast Survey.

IN the year 1849, two citizens of Philadelphia, Horatio Hubbell, Esq., and Col. John H. Sherbourne, presented a lengthy memorial to Congress promulgating a plan for establishing tele graphic communication across the Atlantic ocean; and asking the Government to aid in carrying out the project. This memorial contained the announcement of the probable existence of a table-land or plateau between Newfoundland and Ireland, in the following words.

"Your memorialists proceed to say that from many observations which have been made, there is incontestible evidence of the existence of a submarine table land extending from the banks of Newfoundland across the Atlantic ocean to the mouth of the British Channel." "This is proved by the altered color of the sea water, which has a different appearance, in unfathomable places, from what it has in shallow spots." "This combined with the volcanic construction of Iceland and the Azores, and the situation of that portion of the ocean that lies between these volcanic groups, has led to the conclusion that there has been a lifting up of the bottom of the sea, through the agency of a Plutonic power, and that the bottom thus elevated appears to be cut through, in many places, by deep-water channels." "The appearance of Medusa, Polypi, and other marine creations, seen upon the edge of the discolored water, strengthens this opinion." "Your memorialists propose that these suggestions should be investigated," &c.

The first experiments made to test the truth of these suggestions were the soundings of Commander Berryman, made in the summer of 1853. Previous to this time no cast of the deep-sea lead had ever been made north of the Azores. The soundings of Berryman, and the subsequent soundings of Commander Dayman, have been variously interpreted concerning the proof of the existence of the submarine table-land announced by Messrs. Hubbell and Sherbourne. In a popular sense this announcement conveyed the idea of a vast unbroken level at the bottom of the sea, the existence of which has not been conclusively established by the soundings referred to.

The question, however, is one of very little importance, provided the irregularities of the bottom do not offer any serious obstacle to the safe descent of an electric cable, or cause its destruction subsequently. The question now presented is, taking the bottom of the ocean as it probably exists, with elevations and

depressions corresponding to those found upon the face of the dry land, what influence will these elevations have upon the practical operation of depositing an electric cable, and in the preservation of the electric continuity. Upon this point there has been very little discussion, on account of the popular belief in the existence of a level bottom across the only part of the ocean where a submarine telegraph has been supposed to be practicable. But even upon the line of the Atlantic telegraph, although there may not exist remarkable submarine mountains and valleys, yet it is not improbable that considerable elevations and depressions The profile of Capt. Dayman differed essentially from that of Commander Berryman; so much so as to give rise to serious controversies with regard to the strict correctness of both, since to the probable uncertainties of the soundings, was added the uncertainties in relation to the intermediate depths, the soundings being made generally fifty to one hundred miles apart.

occur.

The explorations of Dayman and Berryman ought therefore to be regarded as general reconnoissances only, from which the true profile of the bottom can only be conjectured. In the explorations of the Gulf Stream by the U. S. Coast Survey, Lieutenants Craven and Maffitt discovered, off Charleston, a series of submarine ridges and depressions several hundred fathoms in height and depth in the horizontal distance of twenty to thirty miles. Such ridges and valleys would have been passed unnoticed in the explorations between Newfoundland and Ireland.

It may be taken for granted that a submarine cable should touch the bottom at every point; otherwise some parts of it must remain suspended across valleys, or chasms, of unknown depth and extent; under these circumstances its continuity is endangered by its weight, its chafing at the points of suspension, the action of currents, and other causes. Whether the Atlantic cable was destroyed by such influences or not will probably never be revealed, but it may be important to examine how far a more accurate and detailed section of the bottom may diminish the risks which must always attend an enterprise of this char

acter.

Such ridges and elevations as were found in the Gulf Stream, though moderate in height and depth when compared with the great depths of the Atlantic, are yet of sufficient magnitude to be taken into account.

The facility with which the ocean is traversed upon its level surface, and its great horizontal extent, compared with its depth, are apt to give rise to inadequate conceptions of the real magnitude of the inequalities of the bottom, inequalities which upon dry land would be overcome with difficulty. But when it

is intended to adapt a line to these inequalities, it is their real and not their comparative magnitudes which must be taken into

account.

An accurate and detailed profile of the bottom is therefore necessary in order to estimate correctly the total amount of cable required to reach from one point to another, following the curve of the bottom, This is importont, not only in determining the total depth of cable necessary to reach from continent to continent, but also to shew at what points a greater or less surplus over the horizontal extent is needed.

It is only by the aid of accurate knowledge upon these points that the practical operation of depositing a cable can be reduced to a positive degree of safety and certainty. It was shown in a paper communicated to the American Association for the Advancement of Science at the Baltimore meeting, April, 1858, that in laying a submarine cable, if the rate of paying out be equal to the speed of the ship, and if the speed of the ship be greater than the rate of descent of the cable in the water, the form assumed by the cable from the ship to the bottom will be a right line, and there will be no tension upon the cable, provided the bottom be a uniform level plain. But if, from depositing upon a level bottom, a descending slope be reached, the cable from the ship to the bottom will form a large catenary, one end of the catenary being at the ship and the other at the crest of the descending slope.

The catenary will produce a dangerous tension upon the cable, if the descent of the slope at the bottom be very deep, unless the speed of the ship be slackened.

The failure of the first attempt to lay the Atlantic cable off the coast of Ireland was doubtless due to this cause. The bottom suddenly fell off from five hundred fathoms to seventeen hundred fathoms, a descent of seven thousand feet, and the same speed being kept up, with nearly the same rate of delivery, it was impossible for the cable to assume the form of the bottom, and a catenary of large dimensions must have been formed, causing the great tension which parted the cable. The same circumstances must occur on a smaller scale when the depression is more moderate, even in deep water: and it may happen that a submarine valley is passed before the cable has had time to descend to the crests; in which case, if the surplus paid out between the crests be insufficient, there must inevitably be a catenary formed from one crest to the other, the effect of which cannot be avoided or foreseen.

It may therefore be safely asserted, that to avoid risk of breaking a cable in the operation of depositing it upon the bottom of the sea, the speed of the ship should be regulated by the depth and form of the bottom. If the principle be adopted of paying out a uniform surplus to suit all the inequalities of the bottom, there

will not only be an unnecessary waste of cable in some places, but the surplus may fail to be sufficient in others, the result of which might be a rupture.

On the other hand, provided an accurate and detailed profile of the bottom be constructed, from which the exact length of cable required between any two points, however near together, can be determined, there is no reason why an irregular form of bottom should present any serious obstacle to the safe deposit of a cable, provided the speed of the ship be so regulated as to deposit the proper amount in the proper place; and it is only by following this rule that risk of breaking from the weight of the cable can be avoided.

In conclusion, the following rules may be stated.

1. Soundings of unquestionable accuracy should be made at intervals not greater than ten miles, and where there is a steep slope of the bottom, at more frequent intervals.

2. From these soundings a profile of the bottom should be made, in sections, upon a large scale, from which the length of the curve of the bottom may be calculated.

3. A chart should be constructed based upon the profile, showing the rate of speed and delivery between the different stations, in order that the cable paid out may adapt itself without tension to the curve of the bottom.

4. The profile and chart should be used as guides in the operation of laying the cable.

There is a popular belief that many parts of the Atlantic across which submarine lines of telegraph have been projected, are filled with mountains and valleys of vast magnitude. All that can be said on this subject is, that the reported measurements of great depths are neither sufficiently accurate or numerous to lead to any probable conjecture of the natural features of the bottom. And the needle-like elevations which have been represented to exist, are more the result of imagination than a representation of facts. Whatever the form of the bottom may be, an accurate profile of it is the only true basis upon which any reliable calculations with regard to the practicability of a submarine telegraph can be made.

And with the help of such accurate profiles even where great irregularities of bottom exist, the risks of failure may not be so great as has generally been supposed. And it is not improbable that the Azores might be made an intermediate station between the two continents notwithstanding the supposed rugged character of the bottom near them; while there is yet no proof that the bottom between the Azores and the Banks of Newfoundland is at all unfavorable to such a project.

ART. VII.-Abstract of a paper on the Ophiurans, a tribe of Starfishes; by Dr. CHR. F. LÜTKEN.*

Terminology and Morphology.

THE body of an Ophiuran consists of a disc, and five or sixt arms issuing therefrom. The disc contains the digestive and reproductive organs and their outward openings, namely: the mouth with its five slits (rimae oris) forming a star in the centre, and twenty (in Ophioderma, &c.) or ten (in Ophiocoma, &c.) genital slits, on the under surface, parallel with and close to the arms. The arms have a solid frame and are supplied with nerves, vessels and muscles, and, by reason of their length and flexibility, acquire, as organs of motions, a perfection quite wanting among the true sea-stars. On its upper surface the disc generally presents an unbroken edge, but below it is invaded by the arms, which pass along its under surface, quite to the mouth-slits. In describing Ophiura the mouth is placed downwards, the back of the disc is therefore the upper surface, towards the periphery is outward, towards the centre inward. The solid parts belong to three different systems, the interior skeleton, the skin skeleton and the surface skeleton. This is the arrangement of Gaudry, though his interpretations are not always right, as will presently be seen. The interior skeleton is nothing more than the ambulacral plates turned upwards and inwards, soldered by their sides in pairs and enclosed by the interambulacral plates. It consists of a series of discoid joints (ossicula ambulacralia-ossicules discoides, GaudryAmbulacralwirbel, Joh. Müller,) which follow each other, like vertebræ, and are connected, partly by a sort of hinge, and partly by muscular bands extending from joint to joint. Each joint has an incision above and below, indicating the line of juncture of the two halves of which it is made up. The outer end of each joint carries a part of the hinge, consisting of three teeth, whereof the lowest runs upwards and is embraced by the two uppermost; on the inner end of the following joint is fixed the corresponding part of the hinge, namely, two edges diverging from each other below, but joined above. On the lower side is a conical cavity for the root of the tentacle.

This is the structure among the typical Ophiurans; but two points, mentioned by Gaudry in Asterophyton, deserve notice. The first is, that, when the arm divides in two equal branches,

* Additamenta ad historiam Ophiudarum. Af det Kgl. danske Videnskabernes Selskabs Skrifter. 5te Række 5te Bind. For this Abstract the Journal is indebted to THEODORE LYMAN of Boston.

In certain species of the genus Ophiactis (Lütken) and in Ophiocoma pumella (Lüt.).

‡ Ánnales des Sciences Naturelles, 3me Serie Zoël. xvi, 339.