When a large engine is required in London, two with 7-inches cylinders are worked together by means of a connecting screw, thus making a jet very nearly equal (as 98 to 100) to that of an engine with cylinders 10 inches diameter. It is also an advantage not unworthy of consideration, that two 7-inch engines may be had nearly for the price of one 10-inch one; so that if one happens to be rendered unserviceable the other may still be available. The usual rate of working an engine of the size described is 40 strokes of each cylinder per minute; this gives 88 gallons. The number of men required to keep steadily at work for three or four hours is 26; upwards of 30 men are sometimes put on when a great length of hose is necessary. The lever is in the proportion of 4-1/4 to 1. With 40 feet of leather hose and a 7/8 inch jet, the pressure is 30 lb. on the square inch; this gives 10.4 lbs. to each man to move a distance of 226 feet in one minute. The friction increases the labour 2-1/2 per cent. for every additional 40 feet of hose, which shows the necessity of having the engine, and of course the supply of water, as close to the fire as is consistent with the safety of the men at the levers. In order that the reader may have a distinct idea of such a fire-engine, I shall here endeavour to give a description, chiefly taken from those made by W. J. Tilley,[K] fire-engine maker, London. The engravings (figs. 1 and 2) represent a fire-engine of 7-inch barrels and 8-inch stroke.[L] The cistern marked A is made of mahogany or oak. The upper work, B, and side-boxes or pockets, C, are of Baltic fir. The sole, D, upon which the barrels stand, and which also contains the valves, is of cast-iron, with covers of the same material, which are screwed down, and the joints made good with leather or india-rubber. The pieces E, at each end of the cast-iron sole D, are of cast brass, and screwed to the cast-iron sole D, with a joint the same as above. In one of these pieces is the screwed suction-cap F, and to the other is attached the air-vessel G, made of sheet-copper, and attached to the piece E by a screw. The exit-pipe H is attached to the under side of the casting E by a swivel. The valves at I are of brass, ground so as to be completely water-tight. The barrels K are of cast brass. The engine is set on four grasshopper springs M. The shafts or handles O, of the levers P, are of lancewood. The box S, under the driving seat, is used for keeping wrenches, cord, &c.; in the fore part of the cistern A, and the box B above the cistern, the hose is kept; the branch and suction-pipes are carried in the side-boxes or pockets C; the rest of the tools and materials are kept along with the above-mentioned articles, in such situations as not to interfere with the working of the engine.