276 Instrument. to measure and register [Ocr. 
H Containing the float, although represented in the figure, must of 
course be placed beneath the floor upon which the tripod is placed : 
it should be as long as the greatest rise and fall which is expected. 
The present machine is adapted for 27 feet of rise; the cireum- 
ference of the cylinder K being rather more than 27 inches, and its 
diameter 82: the wheel F is the same diameter, and the line 0 
must make 12 turns upon it for the whole 27 feet. _ For situations 
where a greater fall is desired, the diameters of the wheels must be 
proportionably increased. 
The only adjustment this instrument requires is, that the clock 
be put in beat by levelling the feet, and regulated to keep good 
time, the line & must be lengthened or shortened until the float 
hangs level with the assumed fixed point from which the heights are 
to be measured. 
If the clock wants altering, it must be stopped when the minute- 
hand points at 10’, and the second-hand at 60”; and then the hour- 
hand must be set at the requisite division; for if the alteration be 
made at any other period, the pencil will not mark when the mi- 
nute-hand arrives at 10’. 
The instrument is made to take to pieces for convenience of car= 
riage. The table B can be removed from the top of the tripod by 
two milled head screws ; the pendulum detached from the clock, 
and fixed close to one of the legs of the tripod; and the weights 
and float to the base; in which state the whole can be put into a 
moderate sized packing case. I am very much indebted to Mr. 
Cary, mathematical instrument-maker, in the Strand, for the 
trouble and pains he took in executing this instrument. 
It is generally admitted that theory alone affords no practical con- 
clusions concerning the flowing and ebbing of the tides: recourse 
must therefore be had to numerous and aceurate observations for 
practical rules to find the times of high and low water. This ma- 
chine will register every ten minutes, with little trouble to the ob- 
server, the variation which takes place from high water to low water, 
and vice versd. As this instrument marks the ascent and descent of 
the water every ten minutes, sufficient datum will be given for find- 
img the nature of the curve described by the tide: and if a register 
of the strength of the wind, and the point of the compass it blew 
from, -was also kept, it might determine whether the wind most 
affected the velocity or the altitude of the tide. If instruments of 
this description were used in different parts of the world, and tables 
‘of the flux and reflux of the tide preserved for a period of 184 years; 
the length of time in which most of the lunar irregularities of mo- 
tion take place, little doubt can be entertained but that as accurate 
tide tables might be made for the rest of the world as have been cal- 
culated for Liverpool by Mr. Noldens, and for the Thames by Capt: 
Huddart. 
Expense, generally speaking, is an objection against purchasing 
an instrument. The one here described, being simple, is propor- 
tionably cheap: and the cost might still be reduced by making the 
clock and the other wheels of wood. As few persons are furnished 
