80 G. H. HALLIGAN. 
ment also involves the use of a larger float in order to carry 
the weight of the tongs. In practice it has been found 
that = inch hollow steel bars with gun-metal pivots + inch 
in diameter meet all requirements, and as the weight of 
the tongs is only 114 Ibs, it is not a serious matter. For 
permanent installations this machine does very well, as it 
is cheap, compact, and is not easily put out of order, but 
for survey work it is not sufficiently portable. It also 
requires a house for its protection from the weather, and 
a well in which the float may work, and in these respects 
it is similar to the other gauges herein described. 
The author has long thought that if the weight of the 
water above the zero of the gauge could be periodically 
recorded, a more compact machine might be constructed 
than any of those now in use. He wishes to record his 
indebtedness to Mr. P. W. Napier of the Harbours and 
Rivers Office of this State, for the idea on which the gauge 
now illustrated was designed. (Plate 3.) 
It consists of a chamber A, about half filled with mercury 
B, to which the sea water has access through the orifice H, 
filling the upper part of the chamber C. A tube D open at 
each end is let into this chamber A, and the mercury has 
access to this tube at the lower end. As the tide rises or 
falls it produces an unequal pressure on the mercury, which 
rises and falls correspondingly in the tube D. A float G 
on the mercury, conveys this motion, by means of the bent 
rod H, to a pen J, by means of which a curve is traced on 
the clock driven cylinder F. The whole instrument is 
inserted in a water-tight case (Plate 3) through the side 
of which the tube EF extends. A level platform about two | 
feet square and about three feet below the level of the 
lowest tide is prepared for each gauge, and care must be 
taken that the machine is lowered on to the clean surface 
of this platform when it is in use. The clock need only be 
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