THE

AMERICAN

JOURNAL OF SCIENCE AND ARTS.

[SECOND SERIES.]

ART. I.-On a new Sounding Apparatus for Deep-sea Sounding; by Prof. W. P. TROWBRIDGE, Assistant U. S. Coast Survey.— With a Plate.

[Published in this Journal by permission of the Treasury Department.] Communication addressed to Prof. A. D. BACHE, Supt. U. S. Coast Survey, dated U. S. Coast Survey Office, Washington, D. C., April 6, 1859.

Dear Sir,-In my report to you of May 31, 1858, I had the honor of presenting the results of an investigation of the laws of descent of heavy bodies in the ocean, under the conditions required in deep-sea sounding.

The object of that investigation was to ascertain and develop fully the causes of failure and error in deep-soundings, and to devise a more certain and reliable mode of measuring the depth of the ocean, in the off-shore hydrography of the Coast Survey, and especially in the swift current of the Gulf Stream.

I have now to present for your further consideration a sounding apparatus based upon the developments given in my former report, and the result of further study and experiments on the subject.

The distinguishing feature of the method herein described, though exceedingly simple in its application, has never before been proposed, inasmuch as its necessity could hardly have been felt, without a careful analysis of the circumstances of descent of the sounding lead and line.

In the method of sounding heretofore employed, the influence of the friction of the water upon the line, or "endwise resist

SECOND SERIES, VOL. XXVIII, No. 82.—JULY, 1859.

ance" as it is called by Prof. Airy, was known to exist, but the amount of this endwise resistance in pounds, and its ultimate effects at great depths, had not been determined. It was supposed that by making use of a weight of thirty or forty pounds and a small fishing line, this resistance would be reduced to an inappreciable amount, or at least that its effect in retarding the descent of the lead would not be sufficient to destroy confidence in the results.

It appears, however, from the investigations referred to, that a weight, such as is ordinarily used in sounding, will be practically held in suspension at no very great depth, even when the line used is the smallest that will sustain the weight with safety in the air; and in confirmation of this conclusion, the fact is well established, that, notwithstanding repeated experiments made by the most skillful officers and with the utmost care, the bottom of the ocean has never been reached in its deepest parts; and even where the bottom has been attained and specimens brought to the surface, the uncertainties of the results have given good grounds for controversy with regard to the depth.

These failures and uncertainties do not arise from the magnitude of the distance to be measured, nor from the impenetrability of the fluid through which the lead has to pass: distances infinitely great and infinitely small in the universe above and around us, have been measured with precision; and the unexplored depths of the ocean are occupied by a medium freely and equally penetrable at all depths. Yet in this field, a field daily traversed by the commerce of the world, a distance of a few miles only has baffled all attempts to measure it.

The difficulty lies in the simple cause stated above, viz. the "endwise resistance" or friction upon the sounding line, which prevents the lead from going to the bottom where the depth is great.

The apparatus which I have devised, is designed to avoid this friction upon the line, while at the same time the line is not dispensed with, but is made use of, as in the ordinary mode.

Before describing this apparatus I will briefly refer to some of the results given in my previous report on this subject.

The rate of descent of an iron globe or sphere, as the simplest geometrical form, was first determined when falling freely in the ocean, and it was found that a sphere will attain a certain maximum velocity, within twenty-five feet of the surface, which velocity will be kept up without sensible increase or diminution to the bottorn.

For a 32 lb. iron shot this uniform velocity is about sixteen feet per second.

The conditions of descent when a small line is attached to the sphere and drawn down with it, were then discussed, the line

being uncoiled from a reel on the deck of the vessel, and drawn down by the weight of the sphere. The friction of this line in the water causes a remarkable change in the rate of descent. Nearly the same maximum velocity at starting is attained, but the velocity becomes rapidly reduced, until the sphere becomes suspended nearly motionless in the water.

Taking the simple case of a 32 lb. shot attached to a small fishing line, the shot attains its maximum velocity of sixteen feet per second within twenty-five feet of the surface, but before a hundred fathoms of the line is drawn into the water, this velocity is reduced to eight feet per second-a diminution of half the velocity from the friction of one hundred fathoms of line. At five hundred fathoms the velocity is again reduced half, or to four feet per second; and at three thousand fathoms to about one foot per second. Whereas at this depth, if there is no line attached, the shot will fall with its original velocity of sixteen feet per second undiminished. Below this depth we may determine, in the same way, the circumstances in the two cases: the shot falling freely still retains its uniform velocity of sixteen feet per second at four, five, and six thousand fathoms depth, while with the line attached, at five thousand fathoms the velocity is reduced to a few inches per second, and at six thousand fathoms the descent is not perceptible under ordinary circumstances.

The time of descent becomes an important element also in practice; in the two cases given, the shot falling freely will descend to the depth of three thousand fathoms in twenty minutes, and to the depth of six thousand fathoms in forty minutes. While with the line attached, it will require two hours to descend three thousand fathoms, and eight hours to descend six thousand fathoms. These effects were shown to be due to the friction alone; the amount of which in pounds, was determined for different cases, in which different forms of weight and differ ent sizes of lines were used; and the entire inapplicability of the ordinary mode of sounding for great depths, and even for ordinary depths, where the object is to obtain a correct knowledge of the depths, was demonstrated.

Methods have been proposed in which a line is dispensed with, by detaching a float at the botton, when the plummet strikes, and watching for the return of the float to the surface; but this is impracticable, as there is no material applicable, within our knowledge, that will float to the surface from the bottom of the sea, on account of the great pressure, which condenses the bulk, so us to render bodies specifically lighter than water at the surface, heavier than water at even moderate depths.

A line must therefore be used to bring back to the surface any machine by which the depth may be registered in the descent.

And the motion of this line in an extended form in the water must be avoided.

The apparatus which I have devised is designed to secure this object, by attaching to the sinker a tube or case in which the sounding line is compactly coiled, and from which it will be discharged freely, thus causing the plummet to carry down the coil, while one end of the line is held fast at the surface; the line being uncoiled from the descending sinker in the manner that a spider falling from a height gives out a thread in his descent by which he retains communication with the point above to which the thread is attached. The motion of the line in an extended form through the water being thus avoided, all the conditions of free descent are secured, and the plummet will descend to the greatest depths with a rapid and uniform velocity.

The depth is ascertained in the manner heretofore known as Massey's method, by a helix or curved blade, which is caused to revolve, by the motion of the apparatus through the water. Instead of Massey's indicator however, which from its faulty construction does not give accurate results, I have adapted Saxton's Current Metre, a much more delicate instrument, to this purpose.

A specimen tube is also used differing somewhat from those now in use, in construction but not in its essential points.

The lower end of the line is attached to the register and to the specimen-box which weigh together only two or three pounds, and as the line is hauled in from the bottom it brings up the register and specimen-box, leaving the plummet and attached case at the bottom.

The details of construction are shown in the accompanying drawings and description of the apparatus.

Besides overcoming the principal difficulty in sounding, there are other important advantages secured by this arrangement which simplify rather than complicate, the problem. These are as follows:

First, there is no strain upon the line, in the descent, except from its own weight, no matter to what depth or with what velocity, the plummet may descend.

ocean.

It is possible therefore to employ a very small line; a single thread of silk may in fact be extended to the bottom of the This permits of the use of a line, which may be coiled compactly within a small space, the strength of the line being made just sufficient to insure its being hauled in with safety, bringing up at the same time the specimen-box and the register. The strain brought upon it, in hauling in, will depend upon the velocity, of the upward motion, which may be regulated accordingly.

Secondly, a rapid and uniform descent being secured, the indications of a revolving register will be reliable when attached to this plummet; while in the present mode of sounding the slow motion of descent at great depths, renders such a mode of registering the depth uncertain and unreliable.

Thirdly, there being no strain upon the line in the descent and the motion being uniform, it is practicable to determine the depth by the time of descent, making use of a small insulated wire as a sounding line, and determining the instant that the weight strikes the bottom by an electrical signal transmitted through the line. An apparatus was devised as long since as the year 1845, for ascertaining the moment when the weight strikes the bottom, by electricity, but in the mode of sounding heretofore employed, no particular advantage would result from this, while the danger of breaking the electric continuity is very great owing to the strain brought upon the line in the descent; and the plummet as now used descends with such a varying velocity, that even with the time of descent given, no calculation will give the depth. The method has therefore never been put in practice. Whereas, in the method proposed, there is no strain upon the line in its descent, and the plummet will fall through each successive hundred fathoms in the same time; the time of descent will thus furnish a simple means of calculating the depth.

In this process it will not be necessary to recover the line, and the time required to sound the ocean at any point, need only be that required for the plummet to sink to the bottom, moving with any velocity which may be desired.

I have made many experiments on the best method of coiling the line so as to secure its uncoiling with certainty, and without the possibility of strain upon the line, or the occurrence of a kink.

I have also given much attention to the quality and size of line to be used: upon these points, the practical working of the apparatus in a certain degree depends, but being merely mechanical questions they are easily settled. They are fully discussed in the description which accompanies the drawings.

The importance of the problem, which is thus sought to be solved, in connection with the survey of the coast, has never been questioned. A knowledge of the configuration of the bottom of the sea, adjacent to the coast, is necessary to the solution of many questions of importance to navigation, and to science, and especially that of the ruling feature of the Atlantic coast, the Gulf Stream; but besides these considerations the question has become one of great public interest in connection with the laying of submarine telegraphs; the risk of such enterprises being diminished in proportion to the accuracy with which the depth of the sea is known at every point of any proposed