168 Dr. Marcet on the specific gravity, and temperature 
tables, taking care to annex to each specific gravity, under the 
head ‘ observations,’ any collateral information which I may be 
able to offer. 
more serious objection of depending for accuracy upon very nice adjustments, which 
can hardly be relied upon under very great pressures. 
Lieut. Fean klin, who commanded his Majesty’s ship the Trent, and was not 
provided with one of Sir Humphry Davy’s machines, sometimes used a cylindrical 
leaden vessel with two valves, like that employed by Dr. Irving ; and at other times 
he made use of an empty corked bottle, the cork being strongly tied to the bottle. In 
every instance the bottle was found filled, the cork having been forced into the 
bottle; except on one occasion, on which the bottle had filled itself without the cork 
being driven in, not apparently from its being more strongly fastened than in other 
cases, but rather probably from its being more porous, so as to allow the water to 
filter through it before the pressure was sufficient to move it from its position. Lieut. 
Franklin had with him my instrument; but he used it only in a few in- 
stances, on account of its being too light to reach great depths, and of too delicate 
a structure to render the addition of a very large weight practicable ; an objection 
however which may very easily be remedied. From all these circumstances it is easy 
to perceive, that the means used for raising water from great depths, have hitherto been 
far from uniform in their principle, or certain in their performance. 
