1839.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



93 



and consequently that the quantity of steam generated by the com- 

 bustion of 841bs. of coal under a pressure of 151b.s on the square inch, 

 and recondenscd without having been allowed to expand, will raise 

 44,4G7,5001bs. one foot high and no more. This we will allow to be 

 the greatest eflcct 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 theend of the stroke 

 even to a lower pressure than that of the atmosphere. But Mr. 

 Palmer attempts to demonstrate that " high pressure steam, M'hen 

 applied expansively, cannot produce so great aneirect as atmospheric 

 8team, 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 lawsofnature,andadducesthe foUowingtheorems ; 

 to prove which he Very unnecessarily occupies seven pages, and then 

 never makes any use of them ; indeeed, 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 theUeast 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 pressui-e, 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 

 that 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 ttiird of the above propositions, gene- 

 rated at the same expense of fuel as that quantity of atmospneric 

 steam ; and yet the elfect will be about double what it would have 

 been if the steam had been worked at the pressure of the atmosphere 

 tlu'oughout 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 woi'k at full pressure during a greater portion of the stroke than if 

 its density increased uniformly with its pressure, in order to fill the 

 cylinder with steam of a given density, which shows that the mean 

 pressure, and consequently the effect, will be greater, the liigher 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 knowii, 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 availinghimself of those advantages, it becomes absolutely 

 necessary that the action of the steam, during that portion of the 

 stroke ol 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 temperatiu-e during its expansion, 

 while (neglecting that lost by radiation, which is a comparatively 



trifluig 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, ])articularly 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 consitlerablc 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 thev 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 efforts 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 we 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 coimtryman 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 winch is not restricted to selfish enjoyment, but 

 brightens the whole human race. 



It is not unaccountable that oblivion should often encloud the ine- 

 mory of the gieatest practical geniuses, for tlieir 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 stoliditv, the inventor is long dead before the contest is ended, or his 

 works are'successfuUy established. In the meanwhile, the progress has 

 been so slow and so gradual, that, like a plant, casts off all 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 aie 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 ofothers 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 

 years soon renders the memory of incidents vague and imperfect. We 

 know 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 ; and it 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 in 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 woridly 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 

 aflairs.he finding work, and Vivian supplying money. It was in part- 



