366 LIE.E.P R.E 
hundred fathoms of the fhore. The only certain method 
of faving the crew of a vefiel infuch a ftate is, to eftablifh 
a rope of communication from the fhore to the fhip. One 
of the plans is, that of throwing from the vefiel into the 
lea an empty calk with a cord attached to it; “the wind 
and the waves would drive the cafk to the fhore, and af¬ 
ford the means of eftablilhing that rope of communication 
already mentioned." Phil. Mag. iv. 250. It feems very 
remarkable, that the anonymous author, who appears to 
have taken much pains to point out means for faving the 
111 ip tv recked, fhould not have thought of fending with 
the empty cafk at lead one man, to make the rope’s end 
fa ft on-fhore, as it mud frequently happen, when a fhip 
is in danger, whether owing to darknefs or to the neared 
land being uninhabited, "that there is no perfon ready to 
lay hold of the rope, and fix it on-fhore, without which it 
can be of no ufe. A very convenient raft for thispurpofe 
might be made by ladling together a few fmall calks and a 
feaman’s ched. Fig. 3, on the preceding Plate, reprefents 
fuch a machine ready for ufe: the apparatus N, to hold 
the perfon upon it, is made from a feaman’s ched with 
holes cut in the iides of it, to allow the perfon within it 
.firmer hold, and to let out the water that may be thrown 
into it from the waves; OO are two pulleys attached to 
the ends of the ched, and through which the line is to 
run ; the raft is to be balladed underneath, to prevent it 
from upfetting. The whole apparatus is fo arranged as 
to be enclofed in a fniall box, and may be feen at the re- 
pofitory of the Society of Arts in the Adelphi. Such a 
machine fhould be kept on-board every fir ip, great and 
fmall. 
When a fhip is leaky, and in danger of finking, it is 
very common to throw her guns and goods overboard, to 
lighten her. In fuch cafes, it would be much eafier, and 
much more effectual, if, indead of throwing away valu¬ 
ables, many of which are but little, if any thing, heavier, 
and fome perhaps are lighter, than fea-water ; cafks con¬ 
taining water, or other liquids of little value, as many as 
might be fufficient, or could be had, were to he emptied 
of their contents, and well bunged ; if tliefe contents could 
be pumped or thrown over-board, the fhip would evi¬ 
dently be lightened of the weight of fuch contents. 
Thus, if calks containing four hogfheads, or one tun of 
water, could be emptied into the fea, the veil'd would be 
lighter by the weight of four hogfheads or one ton of wa¬ 
ter, and would, befules, acquire a new degree of buoyancy, 
fufficient to fupport upwards of one ton of iron or brafs, 
or one ton and a third of dint or done, and many tons of 
goods not much heavier than water. But, allowing that 
the contents of thefe emptied calks do remain on-board, 
the fhip, it is true, carries the fame burden as it did be¬ 
fore they were emptied; but, fhould the ihipfill with wa¬ 
ter, fo as to float the empty cafks, their buoyancy would 
of courfe take place, and prove, that every four empty 
hogfheads, or every four hogllieads of confined air, contri¬ 
bute confiderably more to buoy up the vefiel, than every 
ton of iron or brafs, or many tons of goods little heavier 
than water, could contribute to bear it down and fink it. 
As this new and eafy operation may prove a great fav¬ 
ing, and a mod valuable acquifition, both to our navy and 
commerce, it feems to deferve particular notice. The ef¬ 
fects of confined air for faving goods lighter than iron or 
brafs, would be in proportion to their weight compared 
to the weight of thefe metals in water. Thus, four hogf¬ 
heads, or one ton, of confined air, would contribute more 
to fupport a leaky vefiel than four ton and a half of coal 
would contribute to fink it. Therefore, by emptying four 
hogfheads of their water, and bunging them, four ton and 
a half of coal would be faved ; and, though the water 
from thefe four hogfheads were to remain in the hold, the 
vefiel would be fafer than it would he by throwing the 
four ton and a half of coal into the fea ; and the fame pro¬ 
portion would fubfid for any number of tons of air to four 
times and a half the tons of coal. Of other goods, lighter 
S E R VE1, 
than coal, more might be faved, in proportion to their 
weight in water. 
This method of fupporting leaky veftets would have an¬ 
other great advantage. It would require nothing more 
than to unbung the holes in the beads of the calks ; to let 
the contents run, and to bung the cafks again when empty. 
This might foon be done by one man, indead of employ¬ 
ing many hands in the hard, tedious, and deftruftive, la¬ 
bour of throwing overboard valuable and frequently light 
goods, at a time when men are fo much wanted for other 
necefiary employments. A fnip having a confiderable 
part or the whole of her cargo in cafks, fuch as wine, 
brandy, rum, &c. would never link, were the people, when, 
there appears great danger of finking, to empty and bung 
up as many calks as might fufiice to keep the diip above 
water. The number requifite would be much fmaller 
than it would appear to be at fird fight. Ships at fea, ef- 
pecially thofe of the navy, when part of their cafks have 
been emptied for ufe, are fometimes found too light; for 
which reafon, thofe cafks are filled with fea-water, to add 
to the fliips’ weight, and make them fail deeper and ftea- 
dier. Should fuch fhips become leaky, and threaten to 
founder, it feems evident that they might always be faved 
by emptying and bunging their calks, as has been ex¬ 
plained. 
Confined air might alfo be very ufeful on voyages of 
difcovery, and on other occalions, for reconnoitring hid¬ 
den rocks or fhoals, which impede navigation ; and like- 
wife to facilitate landing on unknown coafls, where the 
land cannot be approached without much danger. A 
boat with air-cafks might attempt to land on almoft any 
fhore ; and, even fhould it be Itaved, the men might be 
faved by clinging to the air-calks. But, were the men in¬ 
dividually provided with fmall air-calks, or life-buoys, 
their lives would be perfeftly fafe, and they might con¬ 
tinue their purfuit, though deprived of both their boat 
and its air-cafks. With their own fmall life-buoys only, 
they might float in deep water, and lfep or (tand upon 
the rocks or fhoals within reach of their feet, and by found¬ 
ing mark fuch as were (till lower in the water. Confined 
air might alfo be ufeful to divers; it would raife them 
rapidly to the furface of the water, after leaving at the 
bottom the weights of Hone requifite to fink them, as is 
pradtifed in the pearl-fifhery. With confined air they 
might reft and breathe on the furface of the water, with¬ 
out a boat, which would frequently not be wanted either 
to convey them to the place of their defcent or to receive 
them on emerging. And a communication, if ufeful, 
might be eftabli'fhed between the furface and the bottom 
of the water, by means of a cord, one end of which might 
be held in the diver’s hand, and the other end attached to 
his weights of ftcne, to be left at the bottom of the water, 
the length of the cord being at lealt equal to tt,e depth of 
the water. 
It has been found by experiment, and is admitted in 
hydroftatics, that a cubic foot of river or frelh water 
weighs about 701b. and a cubic foot of fea-water about 
73lb. This difference, at firft fight, appears by much too 
inconfiderable to jultify what has been aliened, that “half 
the volume of confined air requifite to fupport a man in 
frefh water will fupport him in tea-wateryet it is clearly 
demonftrable, thus: Suppofe a man, weighing 1501b. in 
air, or on land, being immerfed in frelh water, difplaces 
two cubic feet of it; he lofes lo-olb. and retains only iolb, 
of his own weight. The fame man immerfed in fea-water 
alfo difphces two Cubic feet of it, lofes 1461b. and retains 
only ^Ib. of his own weight. In frefh water he is iolb. 
and in fea-water only 41b. heavier than the refpeitive vo¬ 
lume of either water which he difplaces ; and, in order to 
float with his head above the furface, requires artificial 
buoyancy, capable of fupporting iolb. if he be in frelh 
water, and only 4II). if in fea-water. The difference, 
therefore, between the power of fea-water and frefh water, 
for fupporting human bodies, is as 4 to 10, or as 2 to 5; 
