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Show 22 STEAM-ENGINE. NoTE XI. To prevent the cooling of the cylinder by the contaCl: of the external air, he furrounded it with a cafe containing fl:eam, which he again proteCl:ed by a covering of matters which conduCl: heat Oowly. This confiruCl:ion prefentecl an eafy me:ms of regulating the power of the engine, for the fl:eam being the aB:ing power, as the pipe which admits it from the boiler is more or Iefs opened, a greater or fmaller qmntity can enter during the time of a flroke, anJ confequently the engine C:lll aa with exaClly the necefl~ry degree of energy. Mr. Watt gained a patent for his engine in q68, but the !unhcr profecution of his defigns were delayed by other avocations till 1775, when in conjunc1ion with Mr. Boulton, of Soho, near Birmingham, numerous experiments were made on a large fcalc hy their united ingenuity, and great imprOI'Cme nts added to the machinery, and an act of p:u·liament obt:tined for the prolong.Hion of their patent for twenty-fi ve years; they have fince that time drained many of the deep mines in Cornwall, which, but for the happy union of fuch genius, mull: immediately have ceafed to work. One of thcfc engines works a pump of eighteen inches diameter, and upwards of roo fathom or 6oo feet high, at the rate of ten to twelve fl:rokes of [even feet long each, in a minute, and tl1at with one fifth part of the coals which a common engine would have taken to do the fame work. The power of this engine may be eafier comprehended by faying that it raifed a weight equal to 8r,ooo pounds So feet high in a minute, which is equal to the combined action of 200 good horfes. In Newcomen's engine this would have required a cylinder of the enormous diameter of 120 inches, or ten feet; but as in this engine of Mr. Watt and Mr. Boulton the fl:eam acts, and a v:~cuum is made, alternately above and below the pifl-on, the power exerted is double to what the fame cylinder would otherways produce, and is further augmented by an inequality in the length of the two ends of the lever. Thcfe gentlemen have alfo, by other contrivances, applied their engines to the turning of mills for almofl: every purpofe, of which that great pile of machinery, the Albion Mill, is a well known infl:ance. Forges, flitting mills, and other great works are ereB:ed where nature has furnifhed no running ·water, and future times may boafl: that this grand and ufeful engine was invented and perfected in our own country. Since the above article went to the prefs, the Albion Mill is no more; it is fuppofed to have been fet on fire by interefled or malicious incendiaries, and is burnt to the ground. \Vhence London has loft the credit and the advantage of poffeffing the mofl: powerful machine in the world! ( 23 ) N 0 T E XII.------F R 0 ST. In phalam: firm the fiend of Frojl aJ!ail. CANTO. I. 1. 439· TH~ cau_fe of the expanfion of water during its converfton into icc is not yet well afcerta1ned~ It was_ fuppofed to have been owing to the air being fet at liberty in the act of congelatiOn, wh1ch was before diffolved in the water, and the many air bubbles in ice we~e th.ought to co~ntenance this opi_nion. But the great force with which ice expands dunng Its co~gelat1~n~ fo as to hurfliron bombs and coehorns, according to the experiments .of MaJOr WillJ~ms at Q1eb~c, invalidates this idea of the caufe of it, and may fome time be brought 1nto ufe as ~ means of breaking rocks in mining, or projecting cannon-balls, 01: for other mechamcal purpofes, if the means of producing congelation Jhould ever be d1fcovered to be as cafy as the means of producing combufl:ion. Mr. de Maira~ attribu~<': the incre~fe ~f bulk of frozen water to the different arrangement of the particles of It 1~ c?flaiiJ~atwn, as they are conflantly joined at an angle of 6o degrees; and mull: by tlus d1fpofitwn he thinks occupy a greater volume than if they were parallel. He fo~nd the augmentation of the water during freezing to amount to or.e-fourtee~th, one-eighteenth, one-nineteenth, and when the water was previouf1y purged of air to only one-twenty-fecond part. He adds that a piece of ice, which was at firfl: only one-fourteenth part fpecificially lighter than water, on being expofed fome days to the frofl: became vn~-twelfth .lighter than water. Hence he thinks icc by being :xpofed to greater cold n:nwcreafcs 111 volume, and to this attributes the burfling of ice 111 ponds and on the glaciers. See Lewis's Commerce of Arts, p. 257. and the note on M ufchus in the fecond part of this work. This expanfion of ice well accounts for the greater mifchief done by vernal frofl:s attended with moifl:ure, (as by hoar-fro!ts,) than by the dry frofis called black frofl-s. Mr. Lawrence in a letter to Mr. Bradley compbins that the dale-mill: attended with a frofl: on may-d:~y had defiroyed all his tender fmits; though there was a !harper frofl the night before without a mill:, that dicl him no injt1ry; and adds, that a garden not a fione's throw from his own on a higher firuation, being above the dale-mifl:, had received no · damage. Br;1dley, Vol. II. p. 232. . Mr. Hunter by very curious experiments difcovered that the living principle in fifh, 111 vegetables, and even in eggs and feeds, poffeffes a power of refifiing congelation. Phil. Tranf. There can be no doubt but that the exertions of animals to avoid the pain of cold may produce in them a greater quantity of heat, at leafl: for a time, but that vegetables, eggs, or feeds, ihould poffefs fuch a quality is truly wonderful. Others have imagined that animals poffefs a power of preventing themfelves from becoming much warmer than 98 degrees of heat, when immerfed in an atmofphere above that degree of heat. It is true that the increafed exhalation from their bodies will in fome me~fure cool them, os much heat is carried off by the evaporation of fluids, but this is a chemica_! not an animal procefs. The experiments made by thofc who continued |
