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not borne out by "practice." To prove, however, that it is borne out, a table is introduced, showing the "relative consumption of fuel by the Brit ish engines, which use low steain, and some of the fast running American boats, which are worked by steam approaching pretty nearly to the economical pressure of 57 lbs. per square inch."

To render this table complete, we should have the average velocity of the vessels the number of strokes per minute, and the area of the immersed portion of the transverse section. We should then be able to form some idea of the proportion of the engines to the vessel, and of the amount of power expended in obtaining high velocities. Without these elements the comparison, to be fair, should only be between vessels having the same size and moving at the same rate. We should then be better able to oppose "facts" and "theory."

It is hardly necessary to refer in this place to the various statements to be found of the value of the "expansion" mode of working. But two references will suffice. Dr. Lardner in his work on the steam engine, after pointing out the error of Woolf's views, as set forth in his patent, says, " yet so far as his invention suggested the idea of employing steam at very high pressure, and allowing it to expand in a much greater degree than was contemplated either by Watt or Hornblower, it became the means of effecting a considerable saving in fuel, for engines used for pumping on a large scale, the steam being produced under a pressure of forty or fifty pounds, or more upon the square inch," etc. He then goes on to say, that this principle is now applied in the form originally proposed by Watt.

But lest it should be asserted that Dr. Lardner's statements are theoreti cal, we beg leave to refer to the article in the first volume of the Papers of the Institution of Civil Engineers, for a full account of the measured duty of the Cornish engines, together with their consumption of fuel. In these engines the pressure is raised to about 40 lbs. to the square inch, and the steam is cut off at one third, one-fourth one-fifth, one-eighth, or even onetenth of the length of the stroke, according to the work. In the English Journals, numerous statements under the highest authority, show the economy of this mode of working steam, and although intended for quite different purposes, these engines will give some idea of the value of the principle.

The next criticism is upon the opinion expressed by Professor R. as to the mode of improving the performance of the Great Western, stigmatised by Mr. Ward as "grossly erroneous and highly mischievous." This opinion is as follows, "on examining this vessel and comparing her performance with that of American steamboats, it is easy to perceive that her speed might be very materially increased, without making any important change in her engines, and probably with a saving of fuel. It would be necessary to modify the boilers so as to convert a less quantity of water than they now do into steam, but to furnish it of a tension of 20 or 30 lbs. instead of 3, which they now carry, nor when the boiler is of sufficient strength, need any increase of danger be apprehended from using steam of this medium pressure. It is now well established, that the mere pressure

of steam is among the least important causes of danger, and that such as are most to be apprehended are as likely to occur in using steam of a single atmosphere, as that of ten or twelve." The comment runs as follows, "This whole paragraph is made up of errors; but the last sentence, in which is repeated the absurd and dangerous idea that the pressure of steam has little or nothing to do in the bursting of boilers, when such disasters occur, is the most surprising. What else than the pressure of steam ever yet produced an explosion in a steam boiler? What else can find a place in a steam boiler, while at work, to produce one? The existence of any other cause has not only never been proved, either by reasoning or experiment, but the non-existence of other causes which have been supposed to produce explosions, may be inferred from the circumstance, that in every case where the facts could be made out, after an explosion has occurred, the pressure of steam has been found to have been abundantly sufficient to produce the effects observed; and when the same conclusion must be arrived at by reasoning from the known laws of caloric vapor, it is melancholy to find such an opinion promulgated to the world through such a channel, and with the sanction of a respectable name-and it is to be hoped that further reflection, etc." Here is a very serious misapprehension of the latter portion of this "unfortunate opinion." How any one can construe the statement that "the mere pressure of steam is among the least important causes of danger," into one like this, the pressure of steam has little or nothing to do in the bursting of boilers," it is not easy to conceive, if we bear in mind the meaning of the English word mere. If in the first sentence we substitute the words "existence of a boiler," for the words pressure of steam," and we shall have by this new mode of translation, "the existence of a boiler has little or nothing to do in the bursting of boilers." In fact, the whole concluding paragraph contains an insinuation that Professor Renwick believes in the existence of some mysterious agent capable of bursting boilers, ad libitum. Where such belief is expressed, we cannot say; and it is rather remarkable, that in all the writings, conversations, or lectures of Professor Renwick, his opinion should have lain dormant until elicited by this new mode of translation.

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But lest we should be considered as evading, by a mere form of words, we beg once more to refer to authority. Mr. Redfield, in his communication made to the commissioners appointed by the English Government for conducting an inquiry into the causes of steamboat accidents and the practical means of preventing their recurrence, has the following. That the safety of steam boilers from explosions does not necessarily depend upon working with so low a pressure as five or seven pounds to the square inch, and that a reasonable increase in the proportionate strength of the boilers in steam vessels would remove all immediate hazard, and nearly end the catalogue of these disasters, is rendered apparent by the facts which relate to this branch of navigation as it has been carried on in various directions from the city and port of New York." Again, "It must not be supposed

however, that the average pressure of steam now used on the New York steamboats can be greatly increased, without incurring material hazard. The thickness which is found most suitable for boiler metal and the practical and economical limits of form and size, are such as should prevent us from allowing a maximum pressure exceeding one and a half or two atmospheres above the common boiling point, for condensing engines; and an addition of about one atmosphere for high pressure engines, which are worked without a condenser and air pump. To these limits, if an adequate system of boiler construction be adopted, the pressure may with safety be carried, as is done in locomotive engines, in the use of which, owing to a better system of construction, fatal accidents have been less frequent, perhaps, than with low pressure marine engines."

In making the foregoing remarks, we have not pretended to advocate any system of extra high pressure, but merely to point out the fact, that the opinion so severely remarked upon, is not an uncommon one, and that we have the authority of a practical man, and a very cautious one too, for considering that there may be another opinion than the one entertained by Mr. Ward.

The testimony of almost all practical and well informed men is, that the mere use of steam of 40 or 50 pounds pressure per square inch, as in locomotive boilers, etc., is not the cause of danger; and that the use of such pressures in boilers of competent strength, skilfully and carefully managed, is less dangerous, if not more economical, than a low pressure, depended upon as safe, merely because it is a low pressure.

For the American Railroad Journal and Mechanics' Magazine.

ENGLISH AND AMERICAN RAILROADS.

I have lately seen the last half yearly reports of several English railway companies, and thought that a comparison of the results contained therein with those of the American railroads, would be of some interest for your readers, and as the railroads constructed in Massachusetts bear the most resemblance to the English, I have chosen for a comparison the railroads near Boston, for which the last "Annual reports of the railroad corporations in the State of Massachusetts," furnish the necessary data. The following statement is extracted from the reports of five of the most frequented railroads in England.

Cost

Name of Railroad.

per

Length Cost of half year-half year Nett Proportion of 10 whole ly gross ly exprofit. receipts to ir.iles. road. mile. receipts. I penses. expenses. £ Dolls. Dolls. Dolls. Dolls. Liverpool & Manchester 32 1,398,552 211,909) 706,878 401,483 305,395 Grand Junction, 79 1-4 1,900,000 94,756 1,099,422

100 : 57

523,218

576,204

100: 48

London & Greenwich,

London & Birmingham, 112 1-2/5,600,000 241,422|1,674,385 3 3-4 608,000 786,347

681,202

993,183

100: 41

134,078

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Leeds and Selby,

20

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134,054 13,748,8171,795,073 1,953,744

In making the reductions, the pound Sterling is taken at four dollars

eighty-five cents.

98 256

35,798

100: 73

100: 48

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The average cost per mile of the above first four railroads with an aggregate length of 245 miles, is 38,723., or $187,706, while the average half yearly receipts are $14,120 per mile, being at the rate of 15 per cent annually in the cost of the railroads; at the same time the expenditure permile of road was for the half year 6761 dollars, equal to 48 per cent. of the gross revenue, and leaving 7359 dollars as the net profit, which is at the rate of 78 or nearly 8 per cent. per year on the cost of the roads.

It therefore appears that although the railroads in England are constructed at an enormous expense of 187,706 dollars per mile, the nett income per year is nevertheless 8 per cent. on their cost, which favorable result can only be attributed to the immense number of passengers, conveyed annually over these roads. The number of psssengers which passed over the London and Birmingham railroad in the year 1839, was 608,564, of which each performed, at an average, a distance of sixty-five miles. The number of passengers on the Greenwich railroad during the same year, was 1,513,455.

The following is now an analogical statement of five railroads in America, showing the results of their operations in the year 1839.

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The average cost per mile of the first four railroads is $44,394; the Eastern railroad has only been in operation through the year, on a length of 13 miles, the cost of which will not materially differ from the average of $44,394 per mile. The English railroads above specified, are therefore 41 times more expensive than those near Boston; the latter have, however, for the greater part, only single tracks, while the English have double. tracks throughout.

The gross income per mile of road, was $6862, or 15 per cent. of the cost of the roads, which is very near the same as on the English railroads. The expenditure per mile was $2840 (41 per cent. of the income,) leaving as nett revenue per mile $4022, or nine per cent. on the capital expended. Thus it appears that while the gross receipts bear the same proportion to the cost of the railroads both here and in England, the expenses are less here, leaving therefore a greater nett income in proportion to the capital invested.

It is a known fact, that the expenses on railroads do not grow in the same proportion as the traffic increases, and the greater the latter therefore, (the charges for transportation remaining the same,) the better proportion will

the nett profit bear to the gross receipts; that is, while the nett profit on the railroads in Massachusetts is now 59 per cent. should the traffic increase four-fold, the nett profit would be 70 or more, per cent. of the gross receipts. Now the gross receipts on the English railroads above mentioned, are four times as large as on those in Massachusetts, the charges for transportation there, being at least, equally high, and the nett profit is only 52 per cent. of the gross revenue; thus showing that the management of the railroads in America, is in a considerable degree cheaper than in England. Your's truly,

K.

A CONSTANT READER OF THE JOURNAL,

Philadelphia, April 6, 1840.

For the American Railroad Journal and Mechanics' Magazine.

CUBA, ALLEGANY Co., MARCH 27TH, 1840. MESSRS. EDITORS-If the writer of the article on crank motion in your last number (March 15th) will examine Tredgold on the steam engine, vol. I, appendix,p. p. 173 to 182, new edition by Weale-he will find a correct general investigation of the crank motion, by W. S. B. Woolhouse, F. R. A. S., &c.-from the concluding remarks of which, I have copied the following, which may be interesting to some of your readers. Yours, &c., HENRY TRACY.

"We have gone thus far into an investigation of the motion of the crank, as it forms one of the most important instruments of the steam engine, and has hitherto met with very little attention from scientific writers. It is, doubtless, the most simple, and perhaps the most efficient, contrivance, that can be devised to convert a reciprocating into a rotatory motion; and in this respect we cannot be surprised that it has not been superseded by any of the numerous inventions that have been proposed with the view of dispensing with it. We are compelled, however, at the same time, to admit that this beautiful simplicity is accompanied by corresponding inconveniencies, in the inequalities of motion, pressure, friction, and consequent wear. The mechanical defects of engines constructed on the rotatory principle appear to be of greater magnitude, and the disadvantages and difficulties that stand in the way of their application to the most important uses, are of a very formidable nature. This is much to be regretted, as we conceive a perfectly equable motion to be a great desideratum in the steam engine; and the only hope we can have of succeeding in obtaining it is in the exclusive employment of rotary action. On this head we may refer our readers to an instructive paper, entitled "On the Fallacies of the Roatry Steam Engine," by John Scott Russel, Esq., a gentleman to whom practical science is much indebted. One of the leading objects of this paper, which is printed in the Edinburgh New Philosophical Journal for Janurry, 1838, is to show that no loss of power is sustained by the intervention

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