NOTES ON TIDE-GAUGES. 75 
NOTES on TIDE-GAUGES witH A DESCRIPTION oF 
ANEW ONE. 
By G. H. HALLIGAN, L.S., F.G.S. 
[With Plates I. -IIT.] 
[Read before the Royal Society of N. 8. Wales, June 3, 1903. ] 
THE great importance of an accurate knowledge of the 
movements of the tides must be patent to all of us, not 
only from a scientific point of view, but from its direct 
bearing on all commercial matters in which the shipping 
interest is involved. In this country, where most of our 
river entrances have sand bars which can only be crossed 
at certain stages of the tide, a consideration of these 
matters is forced upon us, as most of our harbour works 
are carried out with the object of increasing the tidal scour 
and making the tidal range greater at our river entrances. 
As these circumstances occur at many other places in the 
world, it is not surprising that a large amount of attention 
of inventors and mechanics has been given to the question 
of recording the ebb and flow. in the best and most econ- 
omical manner. The machines which are here illustrated, 
(Plate 1) are intended to show the types generally used in 
various parts of the worid. It willbe seen that they differ 
in the arrangements of the parts; in some the cylinder, on 
which the record is made, is horizontal; in some vertical 
and in others inclined. The majority of gauges have the 
clock outside the cylinder it is designed to drive, though 
why this is done the author fails to see, while some have 
the clocks underneath the machine, and others on top. 
But although dissimilar in details, they are all, with the 
exception of one, which will be referred to later on, con- 
