LIFE-PRESERVER. 663 
Ills plans : “ l fliall only add, that I expect no benefit nor 
advantage whatever to myfelf from my perfeverance and 
labours on this fubjeift, nor reimburfement for an expenfe 
of fome hundred pounds which it has coft me in repeated 
journeys to Edinburgh and London, as well as in expe¬ 
riments, which a living of lefs than feventy pounds a-year 
could very ill afford ; but I fliall neverthelefs reckon my¬ 
felf amply rewarded, if what I have to propofe fliall at 
any time, or in any cafe, prove the means of relieving 
from the deepelt diltrefs, and of refcuing from otherwife 
inevitable death, even a few of thofe who have had the 
misfortune to be involved in the horrors of fliipwreck.” 
The reader will confider with pleafure the philanthropy 
of his heart, which induced him, with fo fmall a portion 
of worldly means, to undertake fo arduous a talk; and 
will contemplate, with furprife, the perfeverance and un¬ 
remitted attention which lie exerted in effecting the ob¬ 
ject; and admire the ingenuity, efficacy, and fimplicity, of 
the means, by which he has effected it. In the hour of 
diffrefs and danger the bleffings of many an unfortunate 
perfon, refeued from a watery grave, will attend his efforts 
in the caufe of humanity. 
In his reply to the fecretary of the Society of Arts, 
(who had acquainted him with the rewards that were de¬ 
creed to him, and the time w-hen they would be deli¬ 
vered,) the feeling mind will regret the neceffity of fucli 
paffages as the following: “Were I to attend in perfon, 
it would altogether defeat the end of the fociety’s bounty. 
My lituation debars me that honour, and I regret it the 
more as I cannot have that opportunity of tellifying to 
liis grace the prefident, and to the fociety, the deep lenfe 
I have of the favour and honour they have done me. I 
truft that my remote diftance will be my humble apology 
to the fociety for my non-attendance, and that you will 
do me the favour to receive the fociety’s rewards for me. 
Whenever I can find a proper opportunity, I will direft 
fome perfon to call upon you for the fame; and I will en¬ 
deavour to get a model of a boat fitted up on my plan, 
and fent to the fociety.” 
The idea of employing empty cafks as life-prefervers 
has been purfued by Mr. Cleghorn, with great fuccefs, in 
his publication called the Hydro-Aeronaut, or Naviga¬ 
tor’s Life-Buoy. He propofes to apply the principle of 
the buoyancy of empty cafks either-in the ffiip, or boat, 
(as by Mr. Bremner,) or outfide the boat, or detached in 
the form of rafts, or on a fmall fcale for faving the lives 
of individuals ; and how fmall a quantity of confined air 
is neceffary to every ufeful purpofe, is a matter which 
might aftoniffi an uninformed perfon, or any one who has 
not confidered the fubjeft; though Mr. Cleghorn’s affer- 
tions will ftand the teft of experiment, as being founded 
on true hydroftatical principles. 
Mr. Cleghorn’s chief aim is to ffiovv, that, without any 
particular precaution, every (hip has almoft always within 
itfelf effe£lual means to prevent the lofs of any of its crew- 
in cafes of fliipwreck ; that man, naturally the moft help- 
lefs of animals in water, may eafily acquire buoyancy fuf- 
ficient to fupport him individually in that element; and 
confequently, that perfons of every defeription may be 
freed from the danger and dread of drowning, and allured, 
that, by a very Ample method, they may be, in mod cafes, 
little more expofed to the lofs of life in water than they 
ufually are when travelling by land. 
A body of any kind floating in water difplaces a vo¬ 
lume of water, whofe weight is exactly equal to the weight 
of fuch floating body. Agreeably to this well-known 
principle, when a man is fufpended in water by the aid 
of two inflated bladders, his weight in water is exaflly 
equal to the weight of water difplaced by the immerfed 
part of the bladders, becaufe in water he lofes all his own 
weight, excepting the weight which the bladders fupport. 
If only one-half of the bladders be under water, one of 
thefe bladders, (if they are alike,) being entirely under 
water, would equally fupport the man. This ffiows, that, 
in order to give any volume of confined air all its buoyant 
power in water, it muff be entirely immerfed, and that a 
much linaller volume of confined air than is ufually fup- 
pofed will fuffice to fupport human bodies and others in 
water. As bladders are too weak to be relied on for ge¬ 
neral ufe, efpecially in dangerous cafes, let it be luppoled 
that the common air here given is confined in fmall calks, 
which we will call air-cajks, or life-buoys , either of wood, 
metal, or any other fuitable fubltance, as will be explained 
hereafter. When a pint, a gallon, or any other meafure, 
of air is mentioned, it is always underftood to mean com¬ 
mon air, or its own buoyancy, abiftrafledly from the wood, 
metal, or other fubftance, in which it may be confined; 
as it is on the buoyancy of the air alone we calculate, 
common air being always nearly of the fame weight, and 
having nearly the fame buoyancy ; whereas the weight of 
wood, metal, or other fubftances, employed to confine the 
air, varies greatly, and muff be confidered apart. Thus a 
pint of air confined in a pint-calk of oak, elm, &c. placed 
in water, has the buoyancy of a pint of air and the addi¬ 
tional buoyancy of the wood which contains it. On the 
contrary, a tin or copper cafe, capable of containing jult 
one pint, has not in water the buoyancy of one pint of 
air, becaufe its buoyancy is diminilhed by the weight of 
the metal, for which an addition of air muff always be 
made, in order that the given volume of air may have its full 
buoyancy. Calks are peculiarly well adapted to the ob- 
je6l in view ; they are to be found ready, and in great 
abundance, wherever man in a civilized ffate exiffs. From 
their lhape, as well as their fubftance, they are ftrong and 
capable of much refinance ; and the common air which 
fills them comes fpontaneoully every where. 
To determine, to a phylical certainty, the ealieff and 
moft effectual means of fupporting human bodies in wa¬ 
ter, and faving them from drowning, only a few Ample 
experiments will be requifite. A pint of confined air 
fupports in frelh water one pound and a half of iron, or 
two pounds of flint or Hone ; confequently, two pints or 
one quart of confined air fupport three pounds of iron ; 
and, in the fame proportion, 14.93$ pints, or not quite 3J 
hoglheads, of confined air, fupport 224.0 pounds, or one 
ton, of iron. Eight pints of confined air have been found,, 
by experiment, to fupport, in frejh water, with his head 
above the furface, a bony man, weighing in air twelve 
ftone. Four pints of confined air fupport the fame man 
in frelh water, with his head all under the furface except¬ 
ing his nofe and mouth. The fame four pints of con¬ 
fined air fupport the fame man, in fea-water, with his head 
above the furface. One pint of confined air (or lefs) fup¬ 
ports the fame man in lea-water with his head all under 
the furface excepting his nofe and mouth. Thefe pro¬ 
portions of confined air, it is thought, will be found fuf- 
ficient for men of almoft any fize, lhape, or weight. 
Thus: In frefi water, two-thirds of a pint of confined air 
for every ltone a man weighs on land, will fupport him 
with his head all above the furface ; but for greater fecu- 
rity, and to render the application more eafy at firft, one 
whole pint per ftone may be allowed. One third of a pint 
of confined air for every ftone will fupport him with his 
head all under the furface excepting his nofe and mouth* 
whether in a perpendicular polture or lying on his back,, 
this lait being preferable; but half a pint of confined air 
per ftone may be granted as above. In lea-water, one third 
of a pint of confined air for every ftone a man weighs, 
will fupport him with his head above the furface; but 
half a pint of confined air per ftone may be granted as 
above. One tw-elfth of a pint of air (or even lefs) for 
every ftone a man weighs, will fupport him with his head 
all under water, excepting his nole and mouth ; but one 
lixth of a pint of confined air per ftone may be granted as 
above. For a detail of the very curious and interefting 
experiments which led to thefe conclufions, we mull refer 
to Mr. Cleghorn’s pamphlet, p. 59 & feq. The whole is 
well deferving of perufal. 
A man then, who would render himfelf buoyant in frelh 
water, if he weighs in common leaks 12 ftone (of 14JIV 
each),* 
