Description of an Hydrometrograph 
an imperfect manner, that errors of one-half the quantity passed 
could neither be avoided nor detected. 
The means formerly made use of for this purpose, at the 
Bavarian "salt-works, and which are generally known, consist in 
employing a certain number of gauge-pipes, or orifices, placed 
in a horizontal line, in the sides of an oblong prismatic vessel ; 
and in which, by the opening or shutting more or fewer of those 
orifices, the surface of the water was endeavoured to be con- 
stantly kept at the same level or height in the vessel, so that its 
surface might form exact tangents to the circles of the apertures 
through which it issued ; and there is no doubt, that an appara- 
tus of this kind, properly adjusted, and diligently attended to, 
is very useful for ascertaining, at any moment, the rate at which 
the water is delivered ; at least, equally accurately as the log, 
when thrown overboard a ship, shews the rate at which the 
ship is sailing, at the time of the observation. But it is evi- 
dent, that unless the supply or delivery of the fluid be perfectly 
uniform and constant, which can hardly ever be the case, this 
method is quite insufficient for ascertaining, with any precision, 
the whole quantity of the fluid delivered in the course of a day, 
a week, or a month ; as each apparatus would require the con- 
stant attendance of a person to regulate the level of the water in 
the gauging-vessel, by opening or closing the orifices of the 
gauge-pipes, according to the diminution or increase of the sup- 
ply ; and, at the same time, to observe and keep an exact ac- 
count of each change or interruption which takes place ; and the 
final result of all this labour, would only be a complicated cal- 
culation, liable to many errors, and, of course, not to be depend- 
ed upon. It was, therefore, a most desirable object, to invent a 
perfectly correct and infallible measurer of the quantity of fluid 
delivered in any given time, independent of every inequality or 
interruption of the supply, which would require no attendance 
whatever, and would record, by its own mechanism, the number 
of cubic feet of fluid delivered, from the commencement of the 
operation, without any other trouble to the observer, than mere- 
ly writing down the numbers indicated by certain indexes upon 
dial plates, in a decade order. 
An experience of many years has proved, that this object has 
been obtained in a most successful manner, from the general use 
