50
HARBOUR ENGINEERING.
In cases where there is any swell, the gauge may consist of a rod or
indicator, with a float at its lower end inclosed in a tube, the bottom of whieh
is perforated as shown in fig. 46. Such an apparatus may be affixed to a quay
or other vertical wall.
In important localities it is customary for tide-gauges to be more
Fia. 46. —Tide-gauge for use in rough Fie. 47. —Tide-gauge House on Quay Wall,
or choppy Water.
elaborately constructed and to possess self-registering apparatus. A well or
tube in free communication with the sea is fitted with a float supporting a
graduated upright stem, which passes upwards to a scale and pointer. For
self-registering purposes the float js çonnected by means of a chain or cord