by the height of the springs and the draught upon the main; the water being only, in some instances, a few inches above the invert of the syphon inlet.

For the removal of air, which would naturally accumulate at the summit level of the syphon, a 4-inch cast-iron air pipe, with lead joints was carried back to the pure-water tank; and for the automatic removal of the air a neat design of pumps and water wheel was supplied, and the whole of the fittings manufactured, in a most satisfactory manner, by the Glenfield Company, Kilmarnock. This machinery is shown in detail in Figs. 3 and 4, in Drawing 2, and the following is a brief description thereof:

The pumps are a pair of diagonal pumps with brass barrels. The pistons are of gun-metal, with a cup leather above and below (the pumps being double acting). The barrels are each set at an angle of 45° from the plumb of the crank shaft, and are worked by one crank pin passing through a bush in a slotted cross-head, of the ordinary donkey-engine pattern; the valves and chests are of gun-metal, metal to metal, of the conical form; access can easily be had to each valve as it is covered by a screwed cup and is in a separate chest. This crank is driven by a water wheel 3 feet in diameter, the sides or shrouding being of cast iron with ribs cast on to carry the buckets. The buckets were made of sheet brass. The small quantity of water required to work the wheel is obtained from the brook and is conveyed from a higher level through an earthenware pipe of small diameter.

Attached to the air pipe is a vacuum gauge, which indicates the presence of air at the summit of the syphon, and so renders unnecessary the constant working of the air pumps.

Although the normal water level is of necessity kept low by the constant draught upon the main, the water being supplied under constant pressure to the town, still with the sluice valves upon the main being closed, the water level in the pure-water tank would naturally be increased.

This syphon has now been in operation nearly seven years, and has so far worked satisfactorily; and although the risk in substituting a syphon for the original line as proposed was no doubt great, still, in the first cost there was a saving of nearly 30007., whilst there is every prospect of a continuance of the satisfactory working of the syphon, and which, after so many years' working, would certainly appear to justify the author's departure from the somewhat hard and fast rule adopted, of having the line of supply

main so situated that in no instance shall it be placed at a higher level than that of the hydraulic mean gradient.

In conclusion, the author desires to state that in determining upon the substitution of a syphon for the straight line of pipe, he was unable to refer to any existing work of a similar description, and he is unaware of any such syphon arrangement having been previously adopted in connection with any similar work of water supply.