202 On the Compressibility of Water. 
generally secured by six layers of cotton or linen cloth, saturated 
in a composition of tar and wax. ‘The first experiment from 
which he draws any conclusion in favour of his hypothesis, is the 
third (see Phil, Mag. vol. Ivii. page 54): the bottle was sunk 
300 fathoms; when drawn up, only a part of the neck remained 
attached. to the line. He concludes that the result was not from 
external pressure, but from the expansion of the condensed sea 
water in the bottle; because the cork was compressed into half 
its length, making folds of about 1-Sth of an inch; and because 
the coverings, consisting of six layers of cloth and cement, had - 
been torn up on one side. Now, from these circumstances, he 
was not entitled to draw the above conclusion ; nor, supposing 
he had proved the pressure from without to have had no con- 
cern in producing the effect, was he entitled to ascribe it to the 
expansion of the water. The great compressibility of air, 
convinces us that little resistance was to be looked for from it to 
the external pressure of the water: the whole must have there- 
fore depended upon the strength of the glass and coverings. Now 
the failure of either of these might be the destruction of the other 
by the force with: which the water would enter, similar to the 
accidents which sometimes occur, when we suddenly cut a piece 
of bladder tied over the top of an exhausted receiver, the glass 
of which is rather thinner than usual. Should therefore the com- 
pactness of the glass and the closeness of the coverings resist the 
entrance of the water, under so great a pressure from without, 
we could expect nothing ‘else but that the coverings should be 
torn, the bottle broken, and the cork probably compressed: or, 
if we suppose the concave bottom of the bottle to have given way, 
then the rush of water upwards, into what we might under that 
pressure, comparatively speaking, call avacuum, would be power- 
ful, and may be supposed to have compressed the cork. — 
But, in the second place, let us for a moment allow with 
Mr. Perkins, that the external pressure did not produce the re- 
sult ; it by no means follows of necessity that the water had been 
compressed, and that it had burst the glass by resuming its for- 
mer volume, when drawn to the surface. The bottles at the time 
they were sent down were filled with air; when the water there- 
fore enters, the air must be absorbed, and this absorption can only 
be maintained by continuing the external pressure: now when 
we draw up the bottle, the water and air will have a tendency 
to separate, and, as the space it formerly occupied is filled with 
water, the elastic force with which it must act will be very great; 
and this accounts for the bottles only coming up whole when a 
space was left at the top by the water, to receive the compressed 
air. In confirmation so far of this, Mr. Perkins remarks, that 
when 
