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] 839.] THE CIVIL ENGINEER AND ARCHITECT’S JOURNAL. 93 and consequently that the quantity of steam generated by the corh- bustion of 841bs. of coal under a pressure of 151bs on the square inch, and recondensed without having been allowed to expand, will raise 44,467,fi001bs. one foot high and no more. This we will allow to be the greatest effect that can be accomplished by atmospheric steam, and yet we assert the possibility of raising not only 70,000,000 but double that quantity, one foot high, by the combustion of the same quantity of coal, by making the steam in a condensing engine perform a part of the stroke at a high pressure, and then causing it to expand through the rest, though it should be reduced at the end of the stroke even to a lower pressure than that of the atmosphere. But Mr. Palmer attempts to demonstrate that “ high pressure steam, when applied expansively, cannot produce so great an effect as atmospheric steam, thereby meaning to infer that no high-pressure engine can perform the same amount of duty as a condensing engine, both con suming equal quantities of fuel.” He professes to draw his arguments from the established laws of nature, and adduces the followingtheorems; to prove which he very unnecessarily occupies seven pages, and then never makes any use of them ; iiuleeed, if he had, they would rather have shown an advantage, both in the use of high-pressure steam and in expanding it. 1. The sum of sensible and latent heat in steam is a constant quantity, viz., about 1172 deg. F. 2. All matter (steam, of course, included), whether solid, liquid, or gaseous, from the most dense and refractory to thejleast ponderable, evolves caloric on compression, or increase of specific gravity, and absorbs caloric on dilatation, or when its specific gravity is diminished. 3. To convert equal quantities of water of any assignable tem perature, and under like pressure into steam of given temperature and elasticity, requires equal weights of fuel to be expended; but, although equal weights of water must absorb equal increments of caloric, when atmospheric steam is generated, it does not follow that all the caloric absorbed in high-pressure steam is exclusively supplied by the fuel expended. The law maintained is simply this, that the same causes produce the same effects. 4. Steam of two, three, or more atmospheres elasticity, is not com posed of two, three, or the like number of volumes of water con tained in an equal volume of atmospheric steam, when generated under the same barometrical pressure, but contains proportionably less water as the pressure under which the steam is generatedincreases. From the first of these theorems we conclude that whatever be the pressure of steam before expansion (so that it be in that state called saturated, that is, as dense as it is possible for it to be at its tem perature), if its density be reduced by expansion to that of steam generated under any given pressure, it will assume the latter pressure and the corresponding temperature, and will therefore be still in the saturated state; so that if steam enter the cylinder of a steam-engine at a pressure of three atmospheres, and, after having performed a little more than one third of the stroke, be made to expand through the rest, so that its density shall be reduced at the end of the stroke to tliat of steam generated under the pressure of the atmosphere; then the cylinder will be filled with steam in every respect the same as atmospheric steam, and, by the third of the above propositions, gene rated at the same expense of fuel as that quantity of atmospheric steam; and yet the effect will be about double what it would have been if the steam had been worked at the pressure of the atmosphere throughout the stroke, for the mean pressure is somewhere near two atmospheres. The fourth proposition shows that the economy of fuel is greater, the greater the pressure is at the commencement of the stroke, for the consumption of fuel is in proportion to the density, which, by the last named proposition, does not increase so rapidly as the pressure. The steam will thus, at a higher pressure, be required to work at full pressure during a greater portion of the stroke than if its density increased uniformly with its pressure, in order to (ill the cylinder with steam of a given density, which shows that the mean pressure, and consequently the effect, Will be greater, the higher the pressure at the beginning of the stroke. The almost incredible advantages to be derived from the expansion of steam becoming every day more generally known, from the ex perience of the Cornish pumping engines, and the adoption of this principle constantly extending itself in consequence, as every body is desirous of availing himself of those advantages, it becomes absolutely necessary that the action of the steam, during that portion of the stroke of the piston through which it expands, should be better un derstood than it is at present, in order that we may be enabled to make a more exact calculation of the power exerted under such circumstances. The present rule for calculating the mean pressure on the piston, when the steam is used expansively is extremely defective; it sup poses the steam to lose none of its temperature during its expansion, while (neglecting that lost by radiation, which is a comparatively trifling quantity) the caloric absorbed by the steam itself in con sequence of its dilatation, which no clothing of the cylinder can pre vent, amounts to many degrees, particularly if, in order to obtain the greatest advantage possible from the principle of expansion, the steam be cut off after the piston has performed but a small portion of the stroke. In this case, the application of the law, that the pressure and density increase in the same ratio, would make the mean pressure appear much more considerable than it really is. We shall attempt, in a future paper, to bring this branch of the theory—we will not say to perfection, for that were presumption, but as near that limit as can be required for practical purposes. MEMOIR OF RICHARD TREVITHICK. While the biography of literary men has received full attention, al though rarely presenting any object of interest, the lives of men of science, deeply enwoven as they are with the history of the pursuits in which they are engaged, have frequently remained unknown, or too often neglected. Nothing, however, can be more interesting to the student, or better calculated to animate him in his career, than the perusal of those eff orts of application and genius, which have overcome impediments apparently unconquerable, or created a giant work from the rudest and most incongruous material. It is here that w r e find the most practical lessons of perseverance, and the most effective stimuli to our exertions: the slow and arduous path to fame is thrown open to our view, and we are taught not to be daunted at the most protracted la bours, and not to neglect the slightest effort for success. When, too, our own countryman is the theme, we warm as we take pride from the halo shining on our native land, and we feel the exalted nature of that genuine fame which is not restricted to selfish enjoyment, but brightens the whole human race. It is not unaccountable that oblivion should often encloud the me mory of the greatest practical geniuses, for their early labours are hid den in the obscurity of the study or the workshop, and then, after bat tling against the efforts of the malignant, or the immoveable resistance of stolidity, the inventor is long dead before the contest is ended, or his works are successfully established. In the meanwhile, the progress has been so slow and so gradual, that, like a plant, casts off ail semblance of the seed, so the name of the author has ceased to keep company with his labours. Often, too, where a name survives, we are led to dis trust, when, like that of an Arkwright, it has supplanted the rightful owner. One of the neglected benefactors of the human race is the subject of the present notice, whose memory, except in his native mines, is among his fellow-countrymen almost consigned to oblivion. At the present period, therefore, when we are beginning to enjoy the benefits of steam locomotion, we have thought that it would be acceptable to present some account of the engineer to whom our country is so much indebted for his efforts in promoting this improvement. We can only regret that this task had not fallen to the lot of others possessed of more ample materials for doing justice to the subject. Although we knew Trevithick during a most active portion of his career, yet the lapse of ears soon renders the memory of incidents vague and imperfect. We now no one, indeed, who could better have fulfilled this task than a late President of the Royal Society, Trevithick’s fellow-countryman and friend. Many errors of omission must therefore be excused, and many misrepresentations palliated; audit must be remembered that we are not so much to blame in committing faults, as that we merit protection for attempting what has not been done before. Richard Trevithick originally moved in that class of society called in Cornwall the Captains of Mines, for which profession he was educated in the mine counting-house as clerk, having as one of his colleagues at that period Richard Griffiths, now the Chief Government Engineer in Ireland. Cornwall, at that period, was something different from what it is now, the mail road not extending beyond Exeter, the Cornish language just extinct, and the great influx of London capital not having commenced. This state of affairs, consequently, did not allow of any superior education ; and although belonging to the mining aristocracy, Trevithick had little but the routine of practice to qualify him for the profession itt which he was destined from his birth to move. Of his early years, therefore, it is unnecessary to say more, than that his career was distinguished by the introduction of many improvements into the operations in which he was engaged, and by a promise of distinction which his future exertions did not belie. The mine captains, from their inter-marriages, were nearly all re lated, and among Trevithick’s nearer cousins were the Vivians. An drew Vivian, one of these, was a man of greater worldly abilities than most of his class, and fertile enough in all those expedients which are useful in raising money. With him Trevithick engaged in several affairs, he finding work, and Vivian supplying money. It was in part-
