REPORT ON THE TIDES. 
193 
may be easily recovered. It should also be carefully stated 
whether the time in which the observations are given is mean 
or apparent, and how obtained. 
The name of the observer, or his initials, should be attached 
to each observation. The simplest method of observation ap¬ 
pears to be by means of a staff, carefully graduated, connected 
with a float, and working through a collar where the height is 
read off. The staff must be kept in a vertical position by 
means of friction rollers ; the float should be in a chamber to 
which the water has access by a small opening, in order that 
the ripple may be as much diminished as possible. It would 
be convenient to have a clock close to the tide gauge ; and if 
made to strike minutes, so much the better. The observer 
should note the height of the water at the end of every minute, 
for half an hour before the expected time of high water, and 
until there can be no doubt that the time of high water is past. 
The minute at which the water stood the highest, or the time 
of high water, is then easily seen. This process is tedious, and 
it might be imagined that it would suffice to note the time when 
the water reaches a certain height shortly before high water, 
and the time when it reaches the same line in its descent; but 
the water rises and falls by jerks, and much too irregularly for 
this plan to be adopted with safety, at least in our river. 
Mr. Palmer has described, in the Philosophical Transactions , 
a self-registering machine which is intended to give the time and 
height of high water ; and I believe it is intended to set one up at 
the London Docks, but I have not heard that it is yet in opera¬ 
tion. The principle consists in a style, or pencil, which is moved 
horizontally by the tide along the summit of a cylinder, which 
is turned round slowly and uniformly ; the pencil describes a 
curve upon paper wound round the cylinder, which curve indi¬ 
cates the fluctuations of the water. The motion of the tide 
being originally vertical, is changed by a common mechanical 
contrivance of the simplest kind. 
When it is intended to make a long series of observations, it 
is of course very desirable to adopt every precaution to ensure 
accuracy ; but many persons have it in their power to make ob¬ 
servations, which may be useful in determining the establish¬ 
ment of a port, or the mean interval between the moon’s south¬ 
ing and the time of high water, without any expensive apparatus. 
For this purpose the observations during one lunation, or even 
less, may suffice, where, as in the river Thames, the rise is con¬ 
siderable and the tides little subject to irregularities. In the 
open ocean, where the rise on the contrary is small, the tide 
often hangs half an hour at high water, and the phaenomena 
N 
