TIDE GAUGE. The phenomena of the tides relate too intimately to physicial science to come fittingly under notice in this work; but tide-ganges, such as that recently erected at Sunderland, are too important to commerce to be passed over here.
Mr. Meik, the engineer of Sunderland has invented and registered a tide-gauge, for the Use of ships entering or leaving a liiirboun In a tidal harbour the number of ships which can enter or leave during one tide depends on the time, the depth, and the rapidity of the tidal flow ; and Mr. Meik wished to produce some sort of gauge which should indicate these conditions, in a way intelligible to ordi• nary seamen, at the busy port of Sunderland, by night as well as by day. In conjunction with Mr. Watson, a brass founder at New castle, Mr. Meik has carried out his project at Sunderland in the following way.
There is a vertical tube, up which the water rises to a greater or less height according to the state of the tide, A float is borne on the surface of the water; and a copper wire from this float passes upWards to a train of wheels and rollers, which rotate in one or other direction according as the float rises or sinks. 1 A web of wire gauze passes from one roller to another; on this web are painted in large letters the various depths from high to low water ; and two fixed pointers also indicate the number of feet and half feet of depth of I water, at any hour of the tide, on the bar at the entrance of Sunderland harbour. By day
the figures on the web are shown white on Et black ground; by night they appear distinctly lighted up, the ground still remaining dark. A white transparent varnish is used for the figures, and an opaque black for the ground. There are also tide tegisteting gauges ern. i played at some ports. There is a vet- t tical tithe, into which the water of a river or harbour can enter from beneath, rising to a greater or less height according to the tide.
A float is on the surfado of the water, and a copper wire passes upwards from the float to a rack which holds a pencil. There is a cylin. der, on the surfaeo of which is fastened a sheet of paper, properly ruled for the and largo enough to receive the entries for fourteen days. A time pied° gives an equable motion to the cylinder ; and as the point of the pencil is in contact with the cylinder, a waving line becomes marked on the paper, passing round the cylinder as time progresses, and passing along the cylinder according as the tide rises arid falls, There thus results a permanent record of the height bf the tide at every hour and even minute of the day.