388 Hydrometrical Observations. 
the land, so that it communicates to it a flavour; so that at 80 leagues 
within the sea, its waters are seen and taste sweet, and in a semicircle of 
100 leagues in circumference, they form a gulph not in the least brackish, 
so that the sailors call it the fresh sea.” 
The instruments now used for obtaining water from different depths, 
are more perfect in their construction than that already alluded to as 
having been used at the Dee, which, as has been seen, was made for a 
temporary purpose. Instruments of various constructions have of late 
been tried for experimenting on this subject ; and as I am not aware that 
any work on marine surveying, or on surveying instruments, contains a 
description of such an apparatus (to which I have applied the name of the 
hydrophore{), the following account of two modifications of it, both of 
which I have been in the habit of using, may perhaps be instructive. 
Fig. 9. represents a hydrophore used for procur- 
ing specimens of water from moderate depths, 
drawn on a scale of one-tenth of the full size. It 
consists of a tight tin cylinder, letter a, having a 
conical valve in its top b, which is represented in 
the diagram as being raised for the admission of 
water. The valve is fixed dead, or immovable, on 
a spindle working in guides, the one resting be- 
tween two uprights of brass above the cylinder 
and the other in its interior, as shewn in faintly 
dotted lines. The valve-rod is by this means 
caused to move ina truly vertical line, and the 
valve attached to it consequently fits the hole in 
the top of the cylinder with greater accuracy than 
if its motion was undirected. A graduated pole 
c, which, in the diagram is shewn broken off, is 
attached to the instrument, its end being inserted 
in the small tin cylinder at the side of the large 
valve or water cylinder, and then fixed by the 
clamp screws shewn in the diagram ; the bottom of the water cylinder 
may be loaded with lead to any extent required. The spindle carrying 
the valve has an eye in its upper extremity to which a cord is attached 
for the purpose of opening the valve when the water is to be admitted, 
and on releasing the cord, it again closes by its own weight. When the 
hydrophore is to be used, the cylinder is lowered to the required depth 
by the pole which is fixed to its side ; or if the depth be greater than the 
range of the pole, it is loaded with weights, and let down by means of a 
rope so attached as to keep it ina vertical position. Care must be taken 
while lowering or raising it, that the small cord by which the valve is 
opened be allowed to hang perfectly free and slack. When the cylinder 
has been lowered as far as is required, the small cord is pulled, and the 
* Page and Pog:a, 
