, fits into a socket e attached to the float. The pin may be pushed into the socket or be withdrawn, by a lever pivoted at
. This pin keeps the float concentric with the trough, but does not bear any part of the weight of the stone. The annular iron trough rests on a bed of cement on a low brick pier built in the form of a hollow octagon.
Fig. 4.
At each corner of the stone were placed four mirrors
