MECHANICS AND USEFUL ARTS. 63 



alone; and the amount of which, in pounds, lias been determined for differ- 

 ent cases, in which different forms of weight and different sixes of line were 

 used; and the entire inapplicability of the ordinary mode of sounding for 

 great depths, or even for ordinary depths, where the object was to obtain a 

 correct knowledge of the depths, has been demonstrated. 



Methods have been proposed, in which a line is dispensed with, by detach- 

 ing a float at the bottom, 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 as 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 Avater, must be avoided. 



The apparatus which Lieut. T. has devised is designed to secure this object, 

 by attaching to the sinker a tube or case, in which the sounding-line is com- 

 pactly 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 but 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 Avill 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 Indi- 

 cator, however, which, from its faulty construction, does not give accurate 

 results, Saxton's Current Meter, a much more delicate instrument, has been 

 adopted 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. Besides overcoming the principal difficulty in sounding, there 

 are other important advantages secured by this arrangement, which simplif}', 

 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. 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 ocean. This 

 permits of the use of a line which may be coiled compactly -within a small 

 space, the strength of the tide 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. 



Second : 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, 

 'enders such a mode of registering the depth uncertain and unreliable. 



