120 NEGRETTI AND ZAMBRA, HOLBOEN VIADUCT, E.G., 



174. Tide Gauge, Self-registering, Wegretti and Zambra's Im- 

 proved Newman's (fig. 125), for recording the rise and fall of the tide, by a 

 lined traced with a pencil on a ruled paper, wound on a cylinder moved round 

 by a clock once in twenty-four hours. The paper showing the rise and fall in 

 feet and inches, and also the time in hours. An exceedingly valuable.instrument 

 for places where the phenomena of tides, and the construction of accurate tide 

 tables are of the utmost importance. Such observations should also be accom- 

 panied with the registration of atmospheric phenomena. 



The tide-gauge, shown in the illustration (fig. 125) consists of a cylinder, 

 A, which is made to revolve once in twenty-four hours by the action of the 

 clock B. A chain, to which is attached the float, D, passes over the wheel, (7, 

 and on the axis of this wheel, (in about the middle of it), is a small toothed 

 wheel, placed so as to be in contact with a large toothed wheel carrying a 

 grooved pulley, E, over which passes a small chain. This chain, passing along 

 the upper surface of the cylinder, A, and round a second pulley, F, at its 

 further end, is acted on by a spring so as to be kept in a constant state of 

 tension. In the middle of this chain a small tube is fixed for carrying a pencil, 

 which, being gently pressed down by means of a small weight on the top of it, 

 marks on the paper placed round the cylinder the progress of the rise or fall of 

 the tide as the cylinder revolves, and as it is drawn by the chain forward or 

 backward by the rise or fall of the float. The paper is prepared with lines 

 equi-distant from each other, to correspond with the hours of the clock, A, 

 crossed by others showing the number of feet of rise and fall. 



The cylinder while in action revolves from left to right to a spectator 

 facing the clock, and the pencil is carried horizontally along the top of this 

 cylinder ; the large wheel, G, is caused to revolve by the rise and fall of the 

 float, which turns the wheel with the small pulley, E, attached to it. If the 

 tide is falling, the small chain is wound round the cylinder, E, and the pencil is 

 drawn towards the large wheel ; brst if the tide is rising, the small chain is 

 wound on the cylinder, F, by means of the spring contained in it. Thus, by 

 means of the rise and fall of the tide, a lateral progress is given to the pencil, 

 while the cylinder is made to revolve on its axis by the clock, so that a line is 

 traced on the paper showing the exact state of the tide continuously, without 

 further attention than is necessary to change the paper once every day, and to 

 keep the pencil carefully pointed ; or a metallic pencil may be used. As indi- 

 cated, it is self-recording, requiring very little attention a few minutes every 

 day being sufficient. 



These gauges are now in action in several parts of the world, faithfully 

 recording the rise and fall of the tides. 



Price, fig. 125, N. and Z's. Improved arrangement, from 50 

 NOTE. The price for the Ruled Papers or Charts used with this Apparatus and 

 No. 175, along with Charts for other Recording Instruments, will be found on page 132. 



