a 
74 Wood's Portable Self-Registering Tide-Gauge. 
from which the true height of the tides may be measured on 
the paper. 
The scale of the register is given on the stand. But it will 
be prudent in all cases to determine the scale by experiment 
on the machine when it has actually been adjusted for use. 
This will be done by moving the float up and down through a 
given height, and measuring the line described by the register 
pencil. 
To prevent the machine from suffering injury, there is a 
stop apparatus attached, of the following kind. A pall is fixed 
on the stand of the machine, and attached to a chain, which 
is wound round the axle X; this chain is of such a length 
as to allow the wheel to travel to its greatest range, either 
way, without interruption ; but should any cause tend to carry 
the wheel farther, the chain draws up the pall to act on a 
stop V, on the edge of the wheel; and so farther motion in 
that direction is prevented. 
The machine here described was made at Port-Glasgow, 
under the superintendence of Mr Wood; and I believe the 
cost of such a machine, with all its appendages, enclosed in a 
suitable box, does pot exceed forty or fifty shillings sterling. 
There are ropes round the large wheel W W in the model ; 
but a simple brass chain might be substituted with advantage, 
to avoid the expansion of the rope, on that side of the wheel 
where the float is attached. 
A plummet is hung at one end of the stand, and a screw at 
each corner serves for setting the machine level; the ropes 
getting deranged when this is not attended to. 
‘Mr Wood also further proposes, in those eases where it 
might not be inconvenient, to connect the machine with a 
clock, having a cylinder DD, shewn in the plate, attached to 
the register already described, so as to give a ¢éme-register 
as well as a height-register. 
For this purpose the travelling-bar T T merely carries an 
additional pencil O called the Time-pencil, which will traverse 
horizontally as the tide rises and falls. The axis of cylin- 
der DD is placed below the time-pencil, and parallel to the 
trayelling-bar. The cylinder revolves once in twenty-four 
