range also raises the steam in the boiler. The steam, in passing into the vessel in which it is condensed, sucks in sufficient air to aërate the water; and after being filtered by a filter attached to the condenser, it

is then ready for use. In passenger ships the engine may be made to drive proper ventilating fans. I consider that every ship ought to be fitted with an engine, as it would increase the safety of the ship, reduce the labour, and add to the comfort of all on board, while it also might be made available, with a simple apparatus, for the slow propulsion of the ship

in calms.

Another form of vertical engine and boiler constructed by Carrett and Co. is shown in fig. 33. Here it will be seen that, as in the previous example, the engine is placed on the top of the boiler, and no foundations are consequently required. The heating surface of this boiler is all formed of boiler plate, and consists of an internal fire box, water box, and uptake flue.

Ordinary direct-acting Vertical Engine.-In the vertical engine of Mr. Ferrabee of Stroud, the crank shaft lies across the top of an appropriate framing, with the cylinder beneath. This engine is represented in fig. 34, which is sufficiently illustrative to enable the material features of the engine to be readily apprehended. The engine is fitted with an expansion valve of the piston construction, and the amount of expansion is regulated by the governor which moves in or out, in an appropriate link motion,

the point which moves the expansion valve; and the amount of its throw is correspondingly affected, and consequently the rate of the expansion. The feed water is heated by the waste steam, and the general design of the engine is very judicious.

Engines for centrifugal pumps.-At the Paris Exhibition of 1867 an engine for driving a fan direct was shown by Mazaline, and Gwynn also had a small and simple horizontal engine driving a centrifugal pump direct.

Fig. 35.

APPOLD'S CENTRIFUGAL PUMP, BY EASTON, AMOS AND SON.

The best form of centrifugal pump is that of Appold with curved vanes, as represented in fig. 35. In 1851 pumps by Appold with straight vanes, with inclined vanes, and with curved vanes, were carefully tested, and it was found that the work done relatively to the power expended amounted with the pump with straight vanes to 24 per cent., with the pump with

inclined vanes to 43 per cent., and with the pump with curved vanes such as are shown in fig. 34— to 68 per cent. This pump has been much used in raising water for irrigation, for draining land and foundations, for pumping out docks, and for various other purposes for which low lifts are required. But for some of these purposes the chain pump formed with square boards moving slowly in a wooden trunk appears to be fully as effective. The centrifugal pump is sometimes driven by toothed wheels, and sometimes by serrated surfaces of contact or the circumferential ridges and furrows known by the name of frictional gearing. But toothed wheels require to work so very fast when the lift is at all considerable, that they are soon cut away, and it appears advisable when gearing is used in such cases to make it spiral, or in steps, and with the teeth bottoming and very broad. If frictional gearing is used, it should be of much greater breadth and power than the authors of that scheme deem necessary, seeing that in certain cases the wheels which have been deemed by them of adequate size have been found quite insufficient to transmit the strain.

Messrs. Easton, Amos & Son combine the pump and the engine to drive it into one structure, and have found, from a carefully-conducted experiment with one of these machines, that with a mean lift of 6 ft. 6 in. nearly, the fan making 124 revolutions per minute, a quantity of water = 6748 cubic feet or nearly 183 tons per minute was delivered. The

engine power as per indicator diagrams, carefully taken, being 111.2 horse power, it follows that the useful work done was in this case 733 per cent. nearly of the power expended.

From several carefully-conducted experiments made by the Court of Policy of Demerara upon one of the pumps in that country, it was found that the useful work done=66-55 per cent. of the power expended, while a well-constructed scoop, tried under precisely similar circumstances, gave no more than 22-3 per cent., and a centrifugal pump of another construction, 29.3 per cent. only.

By the combined system of construction any settlement of foundations which is more or less inevitable in all Fen districts is neutralised, as the whole of the machinery is self-contained, and its working is unaffected by settlement, while the first cost of building foundations and masonry is materially less than by any other plan.

The arrangement of engines employed to drive Appold's centrifugal pump, by Messrs. Easton, Amos & Son of London—by whom large numbers of these pumps are made-is shown in fig. 36. The spindle of the fan is vertical, and is armed at the top with a bevel pinion, to which motion is given by a bevel wheel placed on the shaft of the engine. The fan is contained in a cast-iron casing which also serves to support the engine, and there are two suction pipes, one for each side of the fan. The water drawn in at the centre of the fan is put into rapid rotation by the