31 
of a heavy iron tube over 20 feet in length, weighing* at least a ton. 
In the photograph may be seen the cord, with weight (invisible) 
attached, passing over the small pulley-wheel on the left, and con- 
necting on to the pencil carrier which moves along two parallel 
slides. Attached to the other side of the carrier is the other cord, 
passing round the small wheel on the right, and thence up to the 
clock— an ordinary “Ansona.” At the back of the clock it winds 
round a cylinder fixed to an extension of the centre-arbor. As the 
clock gradually runs down, the weight draws the pencil carriage 
along the slide a distance of approximately twelve inches in the 
twenty-four hours. A long chain, made from bicycle chains, passes 
over two gear-wheels, and attaches to the float on the right-hand 
side (neither float nor any portion of the well appears in the photo- 
graph). The top gear-wheel engages in a small cog-wheel on the 
end of the axis of the drum, and gives the rotary movement to it. 
It is so geared up that a foot rise or fall corresponds closely to half- 
an-inch turn of the drum. The chain passes down over a lazy-pulley 
and is made fast to a counterpoise weight. The cylinder or drum 
is fifteen inches long and six inches in diameter. It is placed hori- 
zontally on a solid stand beyond which one end of its axle projects, 
engaging by the system of gear-wheels mentioned above upon the 
eight-inch B.S.A. wheel. 
In the majority of tide-gauges the pencil is operated by the 
float and the drum, with its axis placed either horizontally or verti- 
cally, is driven round by clock-work. By introducing the above 
radical change in the Port Hedland gauge a more easily decipherable 
tide curve was ensured and a distinct improvement in the adjustment 
of time was expected. For it can be readily understood that it is 
not necessary to depend upon the clock which draws the pencil- 
carriage along, for the time. This is marked on the sheet at the 
beginning and end of a day’s run, and may be obtained from the 
local post-office. The sole purpose of the clock is to give uniform 
motion to the pencil, and so long as its rate does not materially vary 
during each twenty-four hours it is possible to fix with great 
accuracy the exact instant of any point on the tide curve. Thus, if 
the sheet were put on at nine o’clock and taken off at the same time 
next morning, then it is only necessary to divide the horizontal line 
between these two marks into twenty-four equal parts and we have 
every hour of the day marked on the sheet. Two examples of the 
tide curves registered at Port Hedland on this instrument are re- 
produced ( vide Plate IX., Fig. 2, and Plate X.) to show what a clear, 
widely-spaced trace is obtained. It must be borne in mind that they 
are on a scale considerably reduced from the original sheets, which 
measure thirteen inches in length; the height being correspondingly 
increased. Incidentally, the photographs are examples of “spring” 
and “neap” tides respectively and clearly indicate the marked differ- 
ence between the two types. It will be noticed that the high waters 
appear at the bottom of the sheets, which is rather confusing, per- 
haps, but owing to the nature of the gauge it cannot be avoided. 
