120 Sea Log and Sounding Machine. 
To prove how much inconvenience and danger are 
avoided by Massey’s lead, it is enough to state, that 
soundings may be taken in depth from sixty to eighty 
fathoms, while the ship is under way, at the rate of three 
miles an hour ; and as the rate of sailing may be still ma- 
terially reduced, without entirely stopping the vessel, or 
altering her course, so may soundings be had, to any 
depth required, while she is under way. 
In order more clearly to show the superiority of this 
machine, and make it apparent, that the quantity of stray- 
line veered out does not at all affect the truth of the re* 
suit : suppose the common lead thrown from the mizen 
chains of the ship, which may be represented by the point 
a of the triangle a b c, (fig. 5,) 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, in this case, to ascertain the 
exact depth, as a quantity of line, equal to a b , 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 opera- 
tion ceases when it has reached the bottom ; nor is the 
strayline, a 5, whatever its length, at all taken into the ac- 
count. 
It has been found extremely difficult, and sometimes 
impossible, to obtain soundings in very deep water with 
the 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 de- 
scent would be much slower than that of the lead, sepa- 
rately ; it consequently 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 sensi- 
ble check to enable the seaman to know the precise mo- 
ment. Indeed, if he can ascertain even this to a certain 
