of sea waters , in different parts of the ocean , 207 
Explanation of Plate XII. 
Fig. 1. The principle of this improved machine is essen- 
tially the same as that delineated in Plate XI, the valves VV, 
being kept open by means of a weight W, and closing them- 
selves when the weight reaches the bottom. 
The valves in this machine are made of solid brass, and 
they fall by their own weight, so as to close the cylinder, 
the moment that the square FDE, which turns freely upon a 
pivot in P, is depressed in E, where it preponderates, the 
piece cc, which supports the valves, thus becoming unhooked 
from the recession of the hook, or clicket, in F. This may be 
effected in two ways ; • either by the weight W no longer 
pressing on the square in F, so as to keep it fast in its place, 
and therefore suffering it to recede, so as to disengage cc ; or 
by letting down along the line a weight B, that shall fall upon 
DE along the rope A, and disengage the valves by the jerk it 
occasions. This constitutes the improvement by which water 
is now expected to be raised from any given depth, as well as 
from the bottom. 
Fig. 2. This figure does not require any particular refer- 
ences. It represents the instrument in its natural size, which 
simply consists in a glass bulb of moderate thickness, ca- 
pable of holding 844,6 grains of distilled water, with a neck 
or tube issuing from it, and containing a delicate mercurial 
thermometer, the elongated bulb of which is represented in 
dotted lines in the centre of the large bulb. To the end of 
this neck (the diameter of which is near half an inch), a long 
tube having rather a small bore, is ground air-tight, and 
