The last resort, in desperate cases, is to leap from the window. When this is to be attempted, mattresses, beds, straw, or other soft substances, should be collected under the window; a piece of carpet or other strong cloth should be held up by ten or twelve stout men. The person in the window may then leap, as nearly as possible, into the centre of the cloth, and if he has sufficient resolution to take a fair leap, he may escape with comparatively little injury.[J] FIRE-ENGINES. In the application of manual power to the working of fire-engines, the principal object is, to apply the greatest aggregate power to the lightest and smallest machine; that is, suppose two engines of the same size and weight, the one with space for 20 men to work throws 60 gallons per minute; and the other, with space for 30 men, throws 80 gallons in the same time; the latter will be the most useful engine, although each man is not able to do so much work as at the former. The reciprocating motion is generally preferred to the rotary for fire-engines. Independent of its being the most advantageous movement, a greater number of men can be employed at an engine of the same size and weight; there is less liability to accident with people unacquainted with the work, and such as are quite ignorant of either mode of working, work more freely at the reciprocating than the rotary motion. To these reasons may be added, the greater simplicity of the machinery. Various sizes of engines, of different degrees of strength and weight, have been tried, and it is found that a fire-engine with two cylinders of 7 inches diameter, and a stroke of 8 inches, can be made sufficiently strong at 17-1/2 cwt. If 4 cwt. be added for the hose and tools, it will be found quite as heavy as two fast horses can manage, for a distance under six miles, with five firemen and a driver. [Illustration: FIG. 1. Fire-Engine used by the London Fire Brigade. Longitudinal section,--with the Levers turned up for travelling.] This size of engine has been adopted by the Board of Admiralty and the Board of Ordnance, and its use is becoming very general. When engines are made larger, it is seldom that the proper proportions are preserved, and they are generally worked with difficulty, and soon fatigue the men at the levers. [Illustration: FIG. 2. Transverse section.] When an engine is large, it not only requires a considerable number of men to work it, but it is not easily supplied with water; and, above all, _it cannot be moved about with that celerity on which, in a fire-engine establishment, everything depends_. When the engine is brought into actual operation, the effect to be produced depends less on the quantity of water thrown than upon its being made actually to strike the burning materials, the force with which it does so, and the steadiness with which the engine is worked. If the water be steadily directed upon the burning materials, the effect even of a small quantity is astonishing.