76 G. H. HALLIGAN, 
structed on the same principles, so far as the connection 
between the water surface and the recording pencil is con-— 
cerned. Mechanical art has now reached such perfection, 
that little or nothing can be done to improve the working 
parts of many of the gauges now in use, but the connection 
between the water surface and the registering gear has 
always been recognised as the great element of error in all 
tide-gauges. 
In Sydney Harbour, where we have a difference between 
highest high and lowest low water of about seven feet, we 
must allow for a range of nine feet in order to record . 
possible earthquake waves or abnormal tides, the floor, on 
which the gauge table stands, must be, say, three feet above 
highest tides, and if the instrument is three feet above the 
floor it will be 15 feet above the level of lowest water. In 
all gauges (except the Richard gauge, referred to later on) 
this distance is bridged by a flexible band or chain, and it 
is just here that most of the errors creep in. At low water 
about 15 feet of chain is stretched between the float and 
the band wheel, with a very short length on the balance 
weight; but at high water the float is within six feet of 
the wheel, and 10 or 12 feet of the chain or band is then on 
the side of the balance weight. This means that the lower 
six or eight feet of the flexible band or chain is always in 
tension and the remainder is unequally strained in propor- 
tion to its distance from the band wheel at low water. 
The continual change in the disposition of the balance 
weight, means a constantly increasing weight of band or 
chain during flood tide, and its gradual diminution during 
the ebb, has been partly overcome by the use of platinum 
wire of small sectional area in proportion to its length, but — 
in most gauges the old fashioned brass chain or copper band 
is still in use. 
