SMALL WATER SUPPLIES. 



Strut 



42. The planking should be 2 in. or 3 in., and all 

 joints tongued and grooved. 

 They may be square on the top, 

 rounded, bevelled (on the out- 

 side), or the top may be a thin 

 iron plate. The first thing to 

 do when using such a gauge is 

 to find the level of still water 

 A suitable apparatus is shown in fig. 43, 

 and consists of a round brass rod 

 AB, having a hook of brass wire 

 fixed to it and brought to a 

 sharp point. The rod slides 

 vertically in the tube, which is 

 securely fixed to the support. It is 

 split along one side and has a vernier 

 cut upon it ; on the rod AB is a 

 scale of inches and tenths. In use 

 the rod is adjusted so as the 

 hook just causes a small pimple to 

 appear on the water surface. The 

 gauge should be placed some dis- 

 tance back from the gauge, and must 

 be very carefully set so that the top 

 of the hook is exactly dead level with 

 the sill of the gauge when reading 

 zero. The depth of water flowing 

 over the gauge which is ascertained by this ap- 

 paratus effects the flow, inasmuch as the greater 

 the depth the greater the quantity flowing, but also 

 (as we before explained) the head due to the depth 

 causes the velocity to be proportional to the square 

 root of the head. Having set up the apparatus in a 



