he would make himself be waited on, and, in case of sickness, have his food and medicines brought to him, by machines set in motion by his steamengine. I am quite aware that people generally imagine that this smoothness of motion is gained at the expense of power; but they are mistaken, -utterly mistaken! The proverb, "much cry and little wool," (faire beaucoup de bruit et peu de besogne), is true not only in the moral world; it is also an axiom in mechanics. A few words more, and I have done with these technical details. For some years past, it has been found very advantageous not to leave the communication between the cylinder and the boiler free during the whole time of each stroke of the engine. This communication is interrupted when the piston has performed, for instance, a third part of its course; the remaining two-thirds of the length of the cylinder are then traversed in virtue of the momentum acquired, and, above all, by the effect of the expansion of the steam. Watt had early pointed out this method.* Very competent judges have * The principle of the expansion of steam, already clearly indicat ed in a letter from Watt to Dr. Small, dated in 1769, was put in practice at Soho in 1776, and at the Shadwell water-works in 1778, from considerations of economy. The invention and the advantages which were expected from it are described at length in the patent of 1782.-M. ARAGO. The following is the passage in the letter to Dr. Small, above referred to. The letter is dated the 28th of May, 1769:— "I mentioned to you a method of still doubling the effect of the steam, and that tolerably easy, by using the power of steam rushing ïnto a vacuum, at present lost. This would do little more than considered the discovery of expansion not less important, in an economical point of view, than that of the condenser. It is certain, that, since its adoption, the steam-engines in Cornwall are achieving unhoped-for results; that, with one bushel of coal, they do the work of twenty men, working for ten hours. Let us recollect, that, in the coal districts, a bushel of coal costs only ninepence, (about eighteen French sous,) and it will be demonstrated that Watt has reduced, over the greater part of England, the wages of a working man's average day's labour, of ten hours, to less than a sous of our money. double the effect, but it would too much enlarge the vessels to use it all. It is peculiarly applicable to wheel engines, and may supply the want of a condenser where force of steam only is used; for, open one of the steam valves, and admit steam until one-fourth of the distance between it and the next valve is filled with steam, shut the valve, and the steam will continue to expand and to press round the wheel with a diminishing power, ending in one-fourth of its first exertion. The sum of the series you will find greater than onehalf, though only one-fourth steam was used. The power will, indeed, be unequal, but this can be remedied by a fly, or several other ways."-See Edinburgh Review for January 1809, p. 320. For a full account of Mr. Watt's Expansion Engine, and of his patent of 1782, See Robison, STEAM-ENGINE, pp. 126–131, and, still more particularly, Farey, "Treatise on the Steam-Engine," pp. 339-352, where extracts from the specification are given.—TR. * At a time when so many persons are interested about steamengines with a directly rotatory motion, [steam-wheels,] I should be guilty of an unpardonable omission were I not to say, that Watt had not only conceived the idea, as is proved by his letters patent, but even made some of them. These engines were abandoned by him, not because they would not work, but because they appeared to him, in an economical point of view, notably inferior to the double engine with rectilineal strokes. There are few inventions, great or small, of all those which are found so admirably united in the steam-engine, which are not the Numerical calculations give so good an idea of the utility of the inventions of our fellow-member, developement of some of the first ideas of Watt. Trace his labours, and, besides the points of principal importance particularly enumerated above, you will find him proposing engines to act without condensation; engines where, after having performed its office, the steam is dissipated in the atmosphere, intended for localities where there is a difficulty of obtaining cold water in abundance. The expansive principle, to operate in engines with several cylinders, will also figure among the projects of the Soho engineer. He it is who will be found to have suggested the notion of pistons perfectly tight, though composed exclusively of metallic parts;-it is again Watt who will be seen first to have had recourse to mercurial barometers in order to ascertain the elasticity of the steam in the boiler and in the condenser ;-who devised a simple and permanent gauge by means of which the depth of water in the boiler may at any time be seen at a glance ;-who, to prevent troublesome variations of the level, connected the motions of the feed-pump with those of a float; -who, when it was much wanted, applied to a hole in the lid of the principal cylinder of the engine a little apparatus, the indicator, so contrived as to make the law of the evacuation of the steam be exactly known in its relations with the piston, [and to be a measure of the power,] &c. &c. Had time permitted me, I should have shown that Watt was no less skilful and successful in his attempts to improve boilers, to diminish the loss of heat, and to consume completely the clouds of black smoke which escape from ordinary chimneys, to whatever height they may be raised.-M. ARAGO. Mr. Watt, in his notes on Professor Robison, has stated his claim to the application of the crank, upon which he laid little stress, as he conceived it obvious to any one who considered the common foot lathe; and, in fact, it appears to have occurred to others, though probably unknown to him. To him we are unquestionably indebted for the beautiful contrivance of the sun and planet wheels, now little used, but of which we refer our readers to an excellent instance in the steam-engine of the brewery of Messrs. Whitbread and Co. in London, where it has been in successful operation for upwards of fifty years; and there are many others. The sun and planet wheels were adopted about the same time, 1786, in the engines of the great establishment of the Albion Mills, for supplying London with flour, which were destroyed by fire in 1791. See Mr. Watt's note on Robison, Mech. Phil. vol. ii. p. 137, and pl. v. in the same volume. Mr. Watt has there related, that that I cannot resist the desire of laying before you yet two other comparisons. I borrow them from one of the most distinguished correspondents of the Academy, Sir John Herschell. The ascent of Mont Blanc from the valley of Chamouni, is considered, and justly so, as the most toilsome undertaking that a man can perform in two days. Thus, the maximum of mechanical exertion, which we are capable of making in twice twenty-four hours, is measured by the raising the weight of our body to the height of Mont Blanc. This exertion, or its equivalent, a steam-engine will make, by consuming two lbs. of coal. Watt has, then, made it appear, that the strength which a man working for a day can exert, is no more than is contained in a lb. of coal. Herodotus relates* that the construction of the Great Pyramid of Egypt, occupied a hundred thousand men for twenty years. The Pyramid is built of calcareous stone; its cubic contents can be easily calculated; and hence the conclusion is drawn, that its weight is about thirteen millions of millions of lbs. To raise this weight to a height of a hundred and twenty-five English feet, the most valuable assistance in the planning and construction of the mill-work and machinery, was derived from that able mechanician and engineer Mr. John Rennie, then just entering upon business, under whose direction they were executed. They, indeed, formed an era in the history of practical mechanics, and of this country, by the introduction of improved machinery. We have pleasure in recording the intimacy and attachment, which continued through life, between that afterwards widely and justly celebrated civil engineer, and Mr. Boulton and Mr. Watt.-TR. * See Herod. Lib. II. cap. cxxiv.—TR. height of the centre of gravity of the Pyramid, it would be necessary to burn, under the boiler of a steam-engine, six hundred and thirty chalders of coal. There is, among our neighbours, one foundry which I could name, which consumes a greater quantity of fuel every week. COPYING PRESS FOR LETTERS; HEATING BY Birmingham, when Watt went to settle at Soho, could reckon among the inhabitants of its neighbourhood, Priestley, whose name says everything; Darwin, the author of the Zoonomia, and of a well-known poem on the Loves of the Plants ; Withering, an eminent physician and botanist ; Keir, a chemist, distinguished by his Notes on his translation of Macquer, and by an interesting paper on the crystallisation of glass;* Galton, to * He was likewise the author of another paper in the Philosophical Transactions, on the congelation of the vitriolic acid; of a treatise on the different kinds of permanently elastic fluids or gases, in 1777 and 1779; and of a fragment of a Dictionary of Chemistry in 178990, as well as of an Account of the Life and Writings of the wellknown and eccentric philanthropist, Thomas Day, in 1791. Mr. Keir was a gentleman of great literary as well as scientific attainments, but preferred a life of retirement in the bosom of his family, and the society of a few friends, to the allurements of the fame which must have attended him in a more public life. Dr. Darwin had, we believe, removed from Birmingham to Lich |