tubes, set vertically very closely together, conduct the smoke into the chimney. The engine is provided with a small fly-wheel in the usual manner of donkey engines. In their vertical form of engine the boiler is the same as has been already described, but the engine is set with the cylinder inverted, and the pump is of the combined plunger and piston form reinvented by Mr. David Thomson, and first introduced by him in the Richmond Waterworks in 1843. In this form of pump the valves are like those of a common single acting pump, and the area of the plunger is half the area of the piston or bucket. As the piston ascends, the pump sucks itself full of water in the usual manner; but when the piston descends, the water being forced through the valves in the bucket into the space above the bucket, which is too small for it, inasmuch as half the area is occupied by the plunger, it follows that half the water will be forced through the delivery valve when the bucket is descending. The water left in the annular space between the side of the pump and the side of the plunger is forced out when the piston or bucket. ascends; and we thus have the benefit of a doubleacting pump with the gear of a single-acting one. The plunger is open at the top so as to constitute a trunk, and it is properly bolted to the bucket. The trunk and bucket are moved by means of two piston rods proceeding through the cylinder cover, one being placed on one side of the shaft, and the other diagonally on the other side of the shaft. The ar

rangement, in fact, very closely resembles that of Messrs. Napier and Sons' original form of direct-acting screw engine, except that in that case the engine was horizontal. The air pump answers to the water pump in this case; and from the bottom of the trunk a connecting rod proceeds to the crank to turn it round. On one end of the crank shaft is placed a small fly-wheel, and on the other end is an eccentric for working the slide valve, and also the pump employed to feed the boiler. A small piston, acted upon by the water which is being forced out, governs the speed of the engine by opening or shutting the throttle valve.

Messrs. Shand, Mason and Co's. horizontal steam fire-engine is represented in fig. 118, and their vertical engine is similar, but with the cylinder upright. The performance of each class of engine is very nearly the same, and in an experiment made with one of these engines at Messrs. Penn and Son's factory in 1864, with an engine having two cylinders of 6 in. diameter, and 7 in. stroke, the power generated with steam of 120 lbs. pressure in the boiler, and with 152 revolutions per minute, was about 15-horse power. In the case of another engine of the same dimensions, also tried in 1864, the power generated with a little increase in the pressure of the steam was 18-horse power, and the total weight of this engine with its appurtenances was 24 cwt. 2 qrs. In an engine which Messrs. Shand, Mason and Co. sent to the competitive exhibition at Middleburgh,

in Holland, in July 1864, and for which they obtained the gold medal and 500 guilder prize, there was only one cylinder of 7 in. diameter and 8 in. stroke. In an experiment made with this engine, a jet of water 1 in. diameter was projected under a

SHAND, MASON, AND Co.'s HORIZONTAL STEAM FIRE-ENGINE.

water pressure of 125 lbs. per sq. in. With steam of 145 lbs. pressure in the boiler, an average pressure of 128.15 lbs. per sq. in. was maintained upon the piston at a speed of 165 revolutions per minute, and 5 lbs. per sq. in. of back pressure. In this case the

engine exerted 324 actual horse power; and as the total weight of the engine was only 32 cwt. the weight was about 1 cwt. per actual horse power. As this is a very remarkable result, I here introduce a copy of the indicator diagram taken at the time.

INDICATOR DIAGRAM FROM SHAND, MASON, AND Co.'s STEAM

AIR, AND GAS-ENGINE.

In the Paris Exhibition of 1867 Messrs. Shand and Co.'s engine worked with great efficiency, but was not tried officially. In the boiler of these engines the tubes are so thickly set, that it will be important to use pure water, so that there may be no incrustation, which, if considerable, would prevent the access of the water and cement the tubes into a solid mass. It is a necessity of all fire-engine boilers, however, that they should have but little water in them, so that the steam may be quickly got up; and as such engines are never required to work

abundant oppor

for long periods at a time, there is tunity for cleaning the boilers out. By making the upright cylinder which encircles the tubes removable by unscrewing a few bolts, as these makers have done, they provide in a great measure against the only objection that can be made to any of their arrangements.

Prior to the introduction of steam fire-engines, Messrs. Merryweather and Son, of Long Acre, had obtained a high reputation in the construction of hand fire-engines, and also in the construction of other fire apparatus; and in turning their attention to the construction of steam fire-engines they brought to the problem the ripened experience that they had already obtained in other analogous constructions. There are two main features in the mechanism Messrs. Merryweather employ in their steam fireengines-the one is in the boiler, which consists of a number of pendulous tubes hung in a furnace with a smaller internal tube within each, to enable the circulation of the water to be carried on; and the other is in the circumstance of the engine being without a crank, but the pump is worked by being attached to a reciprocating piston, as in Worthington's steam pump, or in the form of donkey-engine introduced by Messrs. Penn, but subsequently abandoned; while the valve of one engine is moved by the other if there are two engines, and by a small independent cylinder and piston if there is only one engine, the valve of this small starting engine being itself moved by a tappet. The benefits which Messrs.