A GRAPHICAL REGISTRER OF TIDES AND WINDS. 
213 
places, the cylinder with the paper will move, and thus by a very simple motion 
from the clock, the real time will be expressed once in the thirty minutes 
around one of the minute points. 
To avoid the risk of inattention on the part of the individual to whom the 
operation of the machine may be intrusted, the machinery connected with the 
float will put the registering apparatus into gear a short time before the time 
of high water, and the clock will put it out of gear when the operation has 
been continued for thirty minutes. 
To obtain the exact time of high water, or even to ascertain it with mode- 
rate precision, does not appear practicable but by means similar to those de- 
scribed. The motion of the surface of the water, occasioned by the wind, 
and the vibrating motion of the general mass upon the turn of the tide, are 
obvious reasons : but by having the float placed in a protected situation, and 
the varying height marked in fact by the time, we may expect to arrive at a 
sufficient accuracy for the purposes required. 
When this machine has been completed, a full description of it shall be for- 
warded to the Royal Society, and I hope it will hereafter do me the honour 
to accept either the original or copies of the series of observations upon the 
tides of the Thames, which both machines may exhibit. 
