ON THE ACTION OF WAVES AND CURRENTS. 521 
20. Appliances for Land Water.—The introduction of land water, 
besides the extension of the pipes for its introduction, required certain 
arrangements for its regular supply in definite quantities. The water 
was to be taken from the town’s mains. And in the first laying down 
the pipes it had been anticipated that it would be sufficient to regulate 
the supply by cocks against the pressure in the mains. Fresh water 
regulated in this way had been from the first supplied in small quantities 
into the generators to ensure the level being kept properly. The experi- 
ence thus gained showed that it was impossible to obtain even approxi- 
mate regularity in this way, as the nearly closed cocks always got choked 
even within twenty-four hours. 
To meet this it was arranged to supply the water through thin-lipped 
circular orifices under a small but constant head of water, which head 
can be regulated to the quantity required. The head of water in the tank 
from which the orifices discharge is regulated by a ball cock, which only 
differs from an ordinary ball cock in that the ball is not fastened directly 
on to the arm of the cock, but is suspended ‘from it by a rod so arranged. 
that the distance of the ball below the arm can be adjusted at pleasure. 
This arrangement has answered well. The cylinder in which the ball 
cock works is made of sheet copper, with a water gauge in the form of a 
vertical glass tube, with a scale behind to show the height of water above 
the orifices, which are made in the bottoms of two lateral projections from 
the sides of the cylinder. One of these orifices feeds the large and the 
other the small tank. The streams from the orifices descend freely 
in the air for about 4 inches, and are then caught in funnels on 
the tops of lead pipes leading to the respective tanks. The cylinder 
is fixed against a wall about 8 feet above the floor, and conveniently near 
the tanks. Any obstruction in the pipes conveying the water to the tanks 
would be at once shown by the overflow of the funnel. The orifices are 
made with areas in proportion to the quantities to be supplied to their 
respective tanks. Then the supply cock connecting the ball cock with 
the main is fully opened, and the ball is adjusted till the quantity sup- 
plied to one of the tanks is correct. The other is then measured ; if this is 
not found correct one of the holes is slightly enlarged until the proportions 
are correct. 
This having once been done for an experiment, no further regulation 
is required except to test the quantities and wipe the edges of the orifice. 
When the tanks are stopped for surveying, the water is shut off from the 
main and simply turned on again on restarting. 
21. The Tide Gauges.—In the experiments made last year a tide gauge 
was used. This gauge consisted of a small tin saucer with a central 
depression in its bottom, in which a vertical wire rested, restraining any 
lateral motion in the float, the wire being guided vertically by a frame 
made to stand on the level surface of the class covers, while the wire 
passed down between two of the covers opened for the purpose, the frame 
carrying a vertical scale. This gauge was used both to adjust the levels 
of the water and to obtain tide curves by observing the heights of the 
tide at definite times and then plotting the curves with the heights of 
the tide as ordinates and the times as abscisse. 
For the earlier experiments this year the same gauge was used for 
both purposes, and it has been used all through: for the purpose of ad- 
justing the levels of the water, automatic arrangements being used for 
drawing the tide curves. 
