4EA LOG AND SOUNDING MACHINE. Q^^ 



In order more clearly to show the superiority of this ma- Its superiority 

 chine, and make it apparent, that the quantity of stray-line ^^^'"P ' '"' 

 yecred out does not at all affect the truth of the result: suppose 

 the common lead thrown from the mizea^hains of the ship, 

 which may be represented by the point a of the triangle ab c^ 

 (fig. 3), and that the ship has moved forwards through the 

 space equal to the line b c, while the lead has descended 

 through the line a c; it is evident, that it is impossible, iu 

 ♦his case, to ascertain the exact depth, as a quantity of line, 

 equal to a bt would be paid out, whereas the true depth is 

 equal only to the line a c, which is much less. But the case 

 is very different when the patent sounding machine is used, 

 as the operation ceases when it has reached the bottom; nor 

 is the stray-line, a by whatever its length, at all taken into 

 the account. 



It has been found extremely difficult, and sometimes im- Takes accu- 

 possibie, to obtain soundings in very deep water with the "^[^""j/.^jet'i'lf* 

 common lead, which may perhaps be thus accounted for. 

 The common line which is used for sounding, though, if left 

 to itself, it would sink in water, yet its descent would be 

 much slower than that of the lead, separately; it conse- 

 quently follows, that the lead must be so much impeded by 

 carrying the line with it, that when it does reach the bottom, 

 there will be scarcely any sensible check to enable the sea- 

 man to know the precise moment. Indeed, if he can ascer- 

 tain even this to a certainty, he still cannot depend upon the 

 truth of his soundings; for if there be the least drift or cur- 

 rent, the line itself will assume a curve, similar to that of 

 the hne of a kite in the air. These two causes will always 

 operate against the perfection of the common mode of 

 mounding. 



After so fully describing the principle of the patent 

 sounding machine, it is scarcely necessary to prove, that it 

 is liable to neither of the foregoing objections; and it may 

 be sufficient to say, that,'as it will certainly find its way to 

 the bottom, if a sufficient portion of stray-line be allowed 

 to guard against its being checked in its progress, and 

 the certainty of its having reached the bottom may be as- 

 certained by the arming, there can be no doubt of the prac- 

 ticability 



