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one thousand, as by a pressure of more than twenty thousand pounds on a square foot.” This, certainly is manifest, but it is also manifest, that if one boiler is so constructed as to be twentyone times the strength of another, it will bear twenty times the force, with less liability to yield to the pressure. A boiler constructed to bear the pressure of ten pounds on the square inch, is certainly more liable to yield to that force, than one capable of bearing a pressure of from three to seven hundred pounds is to a force of one hundred and fifty, the latter being the usual strength and working pressure of the cylindrical boiler. We are told (page 189) that "it is not merely from the boilers' bursting,
that danger arises where a high pressure engine is used; for in
as in the Norwich packet, may carry away the boiler itself,
though boilers may be constructed to bear the required pres'sure, yet the accident on board the Norwich packet, shows that “the boiler itself may be carried away bodily by high steam.” Here is certainly a new discovery in mechanical philosophy, one, the application of which would be more worthy a patent, than all its predecessors. Upon this new principle, steam engines may be constructed which will consist of only a boiler, “ too strong to burst” well bolted down, and highly heated; it will be necessary perhaps to steer stern foremost, as it seems this is the direction in which a boiler is “ carried away bodily by high steam.” If this principle has ever been applied in practice, the writer has never heard of it, except in the well-known trick in the “whole art of Legerdemain,” where we are instructed, “ how to make
dumplins jump out of the pot," by putting a little quicksilver into them before the pot begins to boil; or perhaps in the equally common experiment of standing in a washing-tub, and lifting yourself up by the handles. The fact is, that the boiler on board the Norwich packet was, from its construction, unsafe; a large portion of it was made of cast iron, from its size and thickness in
capable of bearing the pressure of very high steam. Had it been much smaller in its diameter, and the cast iron ends made of a thickness which would have sustained a higher pressure than the wrought iron sides-or in other words, had its construction been like that of the Columbian engine, the fatal accident would never have happened: the side would have had a rent made in it, the fire might have been put out, as has frequently occurred with this engine, the fire-man might have been scalded or killed, which, however, it is believed, has never happened; the rent would have operated as a complete safety valve, the pressure upon the boilers would have been thus instantaneously lessened, and no further evil experienced Before dismissing the subject of danger from explosion, which is certainly the most important of all the controverted points, permit me to add one other remark:-it must be evident that the time of greatest danger is when a boat stops, and the safety valve is not raised. Accident from this cause is more likely to happen in a low, than in a high pressure engine-in the former, a small increase of heat will cause the pressure to rise from 5 or 6 pounds on the inch, to 14 or 15, an increase only of 9 or 10 pounds, which is more than the boilers are intended to bear: in the latter, suppose them to be working with 150 pounds pressure; this must rise to 300, (the lowest estimate of the strength of Evans' boilers) an increase of 150 pounds to the inch, before there is any danger of explosion. This could not happen by accident, as the fire would burn down, before the requisite temperature could be produced. This difference is evinced in the different modes of practice adopted on board the boats in the Delaware. Those with low pressure engines, on arriving at the wharf, immediately raise the valve and suffer the steam to escape, or it is known the boiler would give way. On board the Ætna, working by a high pressure engine, the practice is to close the valve and fire-place, and preserve the steam for future use;* the boiler is thus tested after the passengers have left the boat, as the heat will rise higher than it can whilst the steam is expended in working the engine.
Much more might be said on this part of the subject, but as I fear, Mr. Editor, that you already think I have claimed a full share of your valuable pages, I shall proceed to a short notice of
* Our correspondent must be under a mistake.-ED.
some other points embraced in the “ Review," (page 189) “as to
the permanent expense in fuel,—the writer continues, (page • 189)—“We believe the advantage on fair experiment will be
found in favour of the condensing engine; which under circum6stances equally favourable will afford more power with the same
expense."- (Page 191) “ For this is the true question, what (is the daily expense of fuel.” “ The great expense of an en'gine is the fuel it consumes.”
“ The condensing engines of Bolton and Watt, in Cornwall, in the first four months of the year 1816, raised about twenty. eight and a half millions of pounds of water, one foot height for each bushel of coals consumed."
“ Woolfe's improved double (high pressure) engines, raised upwards of fifty millions of pounds weight, one foot high for eve. 'ry bushel of coal consumed.” Here is certainly a discrepancy which it is difficult to explain: for four months in succession, the high pressure engines produced an effect with the same quantity of fuel, exceeding that of the others as fifty exceeds twenty-eight and a half; yet the writer of the “Review says that, “ as to the per'manent expense of fuel, we believe the advantage, on fair expecriment, will be found in favour of the condensing engine.” As no reason is given for this opinion, and the fact stated invalidates it, we leave it until some evidence is produced, which shall be candidly examined. “The advocates of condensing engines ask, that while machines of this description are so much safer in
comparison than the others--while they are competent to propel a boat against wind and tide nearly six miles an hour, why run so much risk for so little advantage?" (page 191.) This question is certainly very kind; but until the premises are proved, no answer ought to be expected, and when admitted, we shall all be advocates of condensing engines, and there will be no respondent. To guard against the evils apprehended from high pressure engines, we are told that it is proposed (page 193)" to prohibit by legislative interference, the navigating of passage boats by means of high pressure engines, as being dangerous, unnecessary,
and calculated “ to give alarm even when the danger is • slight.” And it is further proposed, that whenever by a long course of experience in manufactories, the high pressure engine
shall be found perfectly harmless, let the act interfering with
them be repealed.” If, as the advocates of condensing engines take for granted, it was proved that the danger slated really existed, there would be soine justice in the proposition; without this proof, it is only leading us back to the period when the exhibition of antimony and mercury was interdicted by law; and exposing ourselves to the pity, or the ridicule of posterity, for rejecting a safe and powerful agent, and retaining only that which is comparatively weak and inefficient. There are many who have well considered the subject, and who have very little doubt, that when the false alarms have subsided, which have been excited by the accidents arising from badly constructed engines, magnified by the fears of some, and the interest of others; the high ssure engine will be generally adopted; particularly for boats, as being lighter, cheaper, more powerful, and safer than the condensing engine. Some of the reasons for this opinion have been briefly stated.With respect to “ the long course of experience in manufacto• ries,” to prove that the high pressure engines are perfectly harmless, we are at a loss to know how long the course of experience must have been continued. The Columbian engine has been used in manufactories for more than ten years; it is said there are about one hundred of them in operation; they have been found to answer the expectations of the purchasers; they have been preferred to the English engine, by those who have used both; they have been found to be perfectly harmless; the proposed conditions have been fulfilled. If these assertions be true, would not legislative interference be ridiculous, unjust, and tyrannical?
Note-Before the above communication was sent to the press, an accident happened, which deserves to be mentioned in this place. The boiler on board the Ætna-a high steam vessel, constructed by Mr. Evans-burst, when the boat was about ten miles from this city. The rent or fissure, through which the steam escaped, was not greater than would have admitted the blade of a pen-knife. As Evans's engine is always provided with three boil. ers, in order to guard against such a casualty, a sufficiency of steam continued to be generated to keep up a pressure of about
70 pounds on the inch, by which the boat was enabled to continue her course.
In the examination of one of the constructors of steam engines before the British House of Commons, who was asked “ what • is the effect when wrought iron gives way?" he answered,“ gene
rally a rent: but I have seen one instance of a wrought iron boiler, where the whole of the upper part was rent from the bottom, driven through the house in which it was placed, and carried to a considerable distance; I believe several yards."-En. P. F.
FOR THE PORT FOLIO.
CRITICISM.-Lalla Rookh; An Oriental Romance, By Thomas Moore.
New-York, 1817. $ 1.
To the very meagre list of British poets who have loitered " in the bowers of Rochnabad" or strayed by “the streams of Mozellay," the attractive name of Moore is now added. More than a year has elapsed since we announced, on the authority of a private letter from the author, that the poem of Lalla Rookh was preparing for the press: indeed every page abounds with evidence of the industry and care with which it has been composed. Whether wandering among the fairy scenes of Persian plains, or gazing at the splendour of her courts, the author has never been dazzlea by the brilliance of the latter, nor lulled into indolence by the seductions of the former. He has returned from this “ voy"age of observation" loaded with the treasures of the cast, and he scatters them before his readers, with the profusion, of a prodigal. “ He has,”-says an ingenious critic, in the last number of the Edinburgh Magazine-he has, by accurate and extensive reading, imbued his mind with so familiar a knowledge of eastern scenery—that we feel as if we were reading the poetry of one of the children of the sun. No European image ever breaks or steels in to destroy the illusion-every tone, and hue, and form, is purely and intensely Asiatic-and the language, faces, forms, dresses, mien, sentiments, passions, actions, and characters of the different agents, are all congenial with the flowery earth, they in