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Show 124 BRAMAH'S PRESS. the same as a screw, the threads of which can be made finer than we can know or even imagine. Thus, as there is no limit to the slowness of the motion of the water, there is none to the greatness ' of the ·power of the press. We shall see in a future section how powerful and general an instrument water is in nature's working; but as it is only men who, like Bramah, understand the properties of substances well, and are at the same time very ingenious as mechanics, that can apply those principles to useful purposes, we, who are not so gifted, can often understand the great principle in nature, from the small application of it by man, better than we can from nature itself. The principle of the press is this: water is forced into a large cylinder through a very small pipe ; and, without making allowance for the friction, the pressure on the cylinder is as many times that on the pipe as the surface of the cylinder contains that of the pipe. If, for example, the little pipe through which the water were forced in had its bore something less than one-tenth of an inch in diameter, and if the cylinder that received the water were about the size of one of the gasometers at the large gas-works, , one man forcing in the water with the· pressure of a single hundred-weight, would communicate so mu.d1 to the water in the cylinder as that it would raise up ten thousand ships of about three thousand tuns each, or move Highgate Hill in one mass ; and a11 that power would be obtained by the application of a very simple principle, of whose operation there are countless instances in nature, together with less w<l:ter than is. contained in an ordinary mill-pond. It IS true that If we were to try such an experiment we shoul~ have som.e difficulty in finding a cylinder; because 1t would gtve way, and give way with a dr~adful explosion, if it were not, at its very weakest pomt, more than able merely to balance the weight of the vast tleet or the entire bill. With us sucb MOTION, LIGHT, AND HEAT. 125 vessels would be out of the question ; but still as we have no occasion to lift large fleets or entire hills,for we take hold ?f other. natural principles, and make the fleets sail, and dig through the hills, or break them up piece and piece by gunpowder -we can have cylinders for water-presses as stro~g as we have any use for. But nature is not limited in her instruments or operations as we are. We are spectators, and can only imitate that which we have found out; whereas that which we call nature is the thing itself which we observe,-all substances and all their properties. Thus, in the resistance of pressure, natu~e can have her apparatus strong, up even to the tearmg asunder even the globe itself; and we know not how many powers in addition to those with which we are acquainted there may be linked together t? prevent that catastrophe; but we do ~now that If a carriage-wheel, made of the toughest non, were made to trundle round at any thing nearly equal to the rate at which the earth moves it would not only be in a moment scattered to at~ms, but th?se atoms W?uld speed away on fire, burning and bemg burnt With more intensity than any furnace that we could kindle or even imagine as being heated by all the art of the founder, and spread conflagration far and wide. Yet that motion of the earth be!lds not the slightest thread which the little spider spms from stubble to stubble in the autumnal field · and it. is as silent as if the mighty careering mas~ were m a state of perfect repose. What eff~ct the rapid ~otions of the earth may hav~ ~pon light and heat IS quite another matter· but I~ IS .a matter so exqv;:.;itely nice and delic.at~ that It w~ll not come at all within the range of our observatiOn. If the earth will not pause in its path round the sun until we can find out the general mfl~1ence which its mo~ions have upon the creatures on Its surface, and their phenomena much less can we hope to question the march of the sunbeams L2 , |
