To get rid of this liability to have a Thor-hammer or thunderbolt generated in the stomach of a steam-engine, at any moment when the vigilance of the engineer happens to be at fault, something is going to be done. No safety-valve or fusible plug is adequate. The boiler cannot be all safety-valve. The trouble is, the hammer is not more likely to strike the first of its terrible series of blows on the valve than anywhere else. A safety-valve, in good order, is a sovereign precaution against the excess of an equally distributed strain, but it is not an adequate protection against a shock or unequal strain. The old-fashioned gaugecocks, which are by no means to be dispensed with, reveal the state of the water in the boiler to the watchful engineer about as surely as the stethoscope reveals to the doctor the condition of his patient's lungs. A surer and more convenient indication is the tubular glass gauge, on the fountain principle, which in its best form is both trustworthy and durable. No well-informed proprietor suffers his boiler to be without one; but it is not a cure for carelessness. It is only a window for the vigilant eye to look through, not the eye itself. Steam-boilers will have to be constructed so that when the subsidence of the water fails to check itself by enlarging the supply, it shall, before the point of danger is reached, infallibly check the combustion, let off the steam, and blow a whistle or ring a bell, which the proprietor may, if he pleases, regard as the official death-knell of the careless engineer. Human vigilance must not be superseded, but fortified,--as in the case of the watchman watched by the tell-tale clock. The steam-creature must be so constituted as to refuse to work itself down to the zone where alone unequal strains are possible; it must cry out in horror and strike work. Mechanically the solution of the problem is easy, and the enhancement in cost of construction will be nothing, compared to the risk of loss from these explosions. With this guard against the deficiency of water, steam-power will become the safest, as it is the most manageable, of all forces that have hitherto been subsidized by the civilized man. But there is one more improvement worth mentioning. We do great injustice to our steam-slaves by the slovenly and unphilosophical way in which we feed them. We take no hints from animal economy or the laws of dietetics.