Hydrometrical Observations. 389 
vessel is immediately filled with the water which is to be found at that 
depth. The cord being then thrown slack, the valve descends and closes 
the opening. The instrument is then slowly raised to the surface by 
means of the rod or rope, as the case may be, care being taken to preserve 
it in a vertical position. This apparatus is only applicable to limited 
depths, but will generally be found to answer all the purposes of the civil 
engineer. 
The form of hydrophore, represented in this figure, is used 
is deep water, to which the small one is inapplicable. It 
consists of an egg-shaped vessel, letter a, made of thick 
lead, to give the apparatus weight, having two valves and 
c, one in the top and another in the bottom, both opening 
upwards ; these valves (which are represented as open in 
the diagram) are, to ensure more perfect fitting, fixed on 
separate spindles, which work in guides, in the same man- 
ner as in the instrument shewn in the last figure. The valves, 
however, in that which I am now describing, are not opened 
by means of a cord, but by the impact of the Projecting part 
d, of the lower spindle on the bottom, when the hydrophore 
is sunk to that depth. By this means, the lower valve is 
forced upwards, and the upper spindle (the lower extremity 
of which is made nearly to touch the upper extremity of the 
lower one, when the valves are shut) is at the same instant 
forced up, carrying along with it the upper valve which al- 
lows the air to escape, and the water rushing in fills the 
vessel. On raising the instrument from the bottom, both valves again 
shut by their own weight and that of the mass of lead d, which forms 
part of the lower spindle. The mode of using this hydrophore is suffi- 
ciently obvious. This instrument weighs about half a hundred weight, 
and has been easily used in from 80 to 40 fathoms’ water in making engi- 
neering surveys, and could, no doubt, be employed for much greater 
depths if necessary. 
In all these experiments, the water being emptied into bottles, is corked 
up, and labelled with certain numbers, which should be entered in a book 
containing remarks as to the place of observation, time of tide, and such 
other particulars as, from the nature of the inquiry, seem to deserve 
notice ; and the water thus preserved may be subjected to analysis, pro= 
duced in evidence, or employed in any other way required by the cir- 
cumstances of the case. 
The marine productions of an estuary, such as the fish, shells, and 
plants which occur in it, occasionally affect questions regarding which 
an engineer may be consulted ; but as it is not my present intention, as 
Stated at the beginning of this chapter, to enter into the nature of the 
questions in which these investigations are required, or the manner in 
which they bear upon them, it is not considered necessary, in mentioning 
these productions, to do more than simply direct attention to the subject. 
