The greatest depth of water in the northern division is 20 feet: it was originally intended to excavate so as to give the water a depth of 20 feet over the whole, but a quantity of rock was left, as the capacity was thought to be sufficient without taking it out. The southern division has 30 feet of water where the bottom was filled in with embankment, and 25 where excavation was made. A portion of rock was left in this division for the same reason as that in the northern division; the greater part of it being in the south-west corner, where it rises above top water line. The capacity of the Reservoir when both divisions are full, is 150,000,000 Imperial gallons. The surface of water in the northern division covers 18.13 acres, and in the southern division, 12.75 acres; making in both nearly 31 acres. Plate XXIII. is a plan of the Receiving Reservoir. The Aqueduct enters a gate chamber at A. where there are regulating gates by which the water can be discharged into the northern division; or into the southern division by a continuation of the Aqueduct within the Reservoir bank to the angle B. of that division. [Illustration: XXIII Scale 200 feet to one inch _F. B. Tower._ _Gimber._ RECEIVING RESERVOIR] A connection pipe of cast iron is placed in the division bank at C. to allow the water to flow from one division into the other in order to equalize the level; it is placed 10 feet below top water line and has a stop-cock to close or open it. At D. is a waste weir, where surplus water may pass off: it is so arranged that the water, when it rises to a proper level, will flow into a well, and from this a brick sewer conducts it off into low grounds, where it finds its way to the East River. At each place where it is designed to discharge water from the Reservoir, a gate house is built far enough into it to reach the greatest depth of water beyond the slope of the embankment. These houses have a wall upon three sides, and the front which faces the centre of the Reservoir has a suitable screen of wood work and wooden gates which regulate the level below the surface for the current of discharge, and the iron pipes leading from these houses have a stop-cock by which the discharge is controlled; this stop-cock is in a vault within the Reservoir bank. The position of these effluent gate houses is marked on the plan by the letters E, F, G, H, there being two in each division. A foot bridge affords convenient access from the bank to the house. Those houses on the east side denoted by E, F, are the ones from which pipes lead to the lower or Distributing Reservoir, and those on the west side denoted by G, H, are intended for supplying the western part of the city north of the Distributing Reservoir.