through a funnel at the centre. This distributor revolved on ball bearings on a central shaft coming up through the centre of the filter. A photograph of this distributor is given on Fig. 24. The objection to the arrangement will be seen in the illustration, namely, the difficulty in constructing a distributor of large size. A large revolving distributor requires stays on the cantilever principle, so that with a filter 60 feet in diameter, the top of the central shaft from which the stay rods spring would be at least 3 feet above the top of the filter; therefore three feet of fall would be lost. With a larger filter the shaft at the centre would have to be higher in proportion, and more fall still would be lost. On this account revolving distributors with an overfeed are only suitable where there is an ample fall at the outfall worksa condition rarely met with-and for small filters. The other revolving distributor with the top-feed, the "Whittaker Bryant," was suspended on an adjustable conical bearing, an arrangement which was remarkably free from friction. There were the same drawbacks to this distributor as to the one already described.

Revolving Distributors fed from below. This obvious limitation to revolving distributors was overcome by feeding the central chamber from below. Here, again, a difficulty presented itself. The joint where the revolving arm moved on the fixed central shaft was the weak spot. The danger was that the joint would either leak-or if tight enough not to leak, there would be so much friction that the apparatus would not revolve. This difficulty has been obviated by English engineers in three different methods.

The Candy Distributor. The syndicate representing the Candy and the Whittaker Bryant Sprinkler have introduced a most ingenious mercurial seal (Fig. 25), which permits the adoption of a perfectly easy frictionless joint.

A plan and section of the central feed of this distributor are shown in the accompanying plate (Figs. 26, 27). The sewage passes from the feed chamber up the central shaft; then through the upright longitudinal holes into the cylinder into which the perforated arms are fixed. This cylinder is suspended on ball-bearings from the top of the central shaft. The cylinder is open above, and below it fits into a groove a couple of inches deep, which is filled with mercury. To keep

the cylinder in its place, and to prevent lateral oscillations, it is also provided below with ball-bearings. The feedchamber is fixed a foot or so above the level of the perforated arms. The sewage rises inside the cylinder some thirteen inches with this head, the mercury being about thirteen times heavier than sewage. The only outlet for the sewage is therefore through the perforations in the movable pipe, which turns round with a head of about a foot. The author has four of these distributors in his district, and they are quite a success. The results of analyses of the effluent obtained are given on p. 142.

Messrs. Adams' Cresset Distributor.-Messrs. Adams have overcome the friction difficulty by adopting for their joint an air-lock between two water-seals. A section through Messrs. Adams' "Cresset" distributor is given in Fig. 28, and an illustration of the distributor at work in Fig. 29. There is no loss of head other than that required to revolve the apparatus, the sewage rising in the central chamber to the same level as in the feed tank. The ball-bearings upon which the distributor revolves, work in a race supported upon the central column, well above water level and protected from rain. A lubricator is fitted upon the cross head by means of which the ball race is kept oiled. The arms are stayed with steel guy ropes. Messrs. Adams generally have four revolving arms instead of two, but there does not appear to the writer to be any special advantage in this. It is obvious that by reduplicating the number of water-seals the head working the distributor can be increased to any extent within reason. This make of distributor is working satisfactorily at Buxton and Chesterfield in the author's district.

Messrs. Mather and Platt's Revolving Trough Distributor. The revolving distributors already described are actuated on the principle of Barker's Mill. Messrs. Mather and Platt have introduced a turbine into their distributor, and have adopted a trough instead of a pipe for distributing the sewage. The trough is easier to clean than a perforated pipe, and as the apparatus is turned by the turbine, a perforated pipe is not necessary to utilize the trajectory force of the sewage issuing from the holes in the distributor. It is, therefore, possible to have a much larger number of holes, and have them closer together than is the case with the revolving