To answer which, please to observe the use of the small boiler, _d_, when it is thought fit by the person tending the engine to replenish the great boiler, which requires an hour and a half, or two hours’ time to the sinking one foot of water; then, I say, by turning the cock of the small boiler, _e_, you cut off all communication between _s_, the great force-pipe, and _d_, the small boiler, by which means _d_ grows immediately hot, by throwing a little fire into _b_, and the water of which boils, and in a very little time it gains more strength than the great boiler; for the force of the great boiler being perpetually spending and going out, and the other winding up, or increasing, it is not long before the force in _d_ exceeds that in _l_, so that the water in _d_ being depressed in _d_ by its own steam or vapour, must necessarily rise through the pipe, _h_, opening the clack, _i_, and so go through the pipe, _k_, into _l_, running till the surface of the water in _d_ is equal to the bottom of the pit, _h_; then steam and water going together, will, by a noise in the clack, _i_, give sufficient assurance that _d_ has discharged and emptied itself into _l_, to within eight inches of the bottom; and inasmuch as, from the top of _d_ to the bottom of its pipe, _h_, is contained about as much water as will replenish _l_, one foot, so you may be certain _l_ is replenished one foot of course; then you open the cock, _i_, and refill _d_ immediately; so that here is a constant motion without fear or danger of disorder, or decay, if you would, at any time, know if the great boiler, _l_, be more than half exhausted, turn the small cock, _n_, whose pipe will deliver water, if the water be above the level of its bottom, which is half way down the boiler; if not, it will deliver steam. So, likewise, will _g_ show you if you have more or less than eight inches of water in _d_, by which means nothing but a stupid and wilful neglect, or mischievous design, carried on for some hours, can any ways hurt the engine; and if a master is suspicious of the design of a servant to do mischief, it is easily discovered by those gauge-pipes; for if he come when the engine is at work, and find the surface, _c_, of the water in _l_, below the bottom of the gauge-pipe, _n_, or the water in _d_ below the bottom of _g_, such a servant deserves correction, though three hours after that, the working on would not damage or exhaust the boilers; as that, in a word, the clacks being in all water-works always found the better the longer they are used, and all the moving parts of our engine being of like nature, the furnace being made of Stourbridge, or Windsor brick, or fire-stone, I do not see it possible for the engine to decay in many years; for the clacks, boxes, and mitre-pipe, regulator, and cocks, are all of brass; and the vessels made of the best hammered copper, of sufficient thickness to sustain the force of the working the engine.