er-are the data for the analysis of the evaporative effects; the true causes of which in the several experiments, the author now attempts to develope. The authentic facts here recorded of the working of boilers and engines of established credit and notoriety, will enable the employer of any boiler or engine to compare his practice with specimens of acknowledged and wellattested merit. The results derived from the above data are arranged in a tabular form, so as to exhibit at once the relation which any one property and the several parts of the boiler bear to any other, and to the effects produced, the amount and activity of the combustion (to which the author assigns the term calorific forces,) and the modifications it experiences by the structure and disposition of the several parts. There are also certain quantities and relations which exert a peculiar influence over the results, which, being rightly ascertained, are exponential or indicative of the practice of each particular boiler; these Mr. Parkes calls the exponents of that boiler, and are as follows: The quantity of coal burnt under a boiler in a given time, the quantity burnt on each square foot of grate per hour,-the quantity of water evaporated per square foot of heated surface-and the number of pounds of water evaporated by a given quantity of coal. Besides this, the influence of time, that is, the time of duration of any given portion of heat about a boiler, and about equal areas of surface, demands our most attentive consideration, and is especially treated of at the close of the paper. It appears most distinctly, that the boilers tested as to their merit by their respective evaporative economy, arrange themselves in the inverse order of the rate of combustionthe Cornish boiler being greatly superior to all the others when tested in this manner, as well as also as in respect of time is selected as the standard of comparison, whereby to mark the scale of descent from the highest point of excellence yet attained in evaporative economy. For this purpose, then, the Cornish results are considered as unity. The value of the exponents for the Cornish, Wagon and Locomotive boiler respectively, are collected together in the following table, which will serve to show at one glance the respective values of the boilers on this comparison. Boiler. lbs. Cornish 10. of Coal burnt under one boiler in 44.08. seconds. 1.0. of Coke ditto in 1657. ditto. in 6:45. ditto. Locomotive Cornish 34. of Coal burnt on each square foot of grate per hour. ditto ditto 10. of Water evaporated by 1 square foot of heated surface per hour from 212°. Cornish ditto ditto 118. of Water evaporated by 1 lb. of coal from 212o. 8.8. ditto Cornish ditto 1 lb. of Coke, ditto Locomotive 5.4.1 ditto 1 lb. of Coal, ditto The Cornish boiler possesses some peculiar advantages, both as regards structure and the practice of slow combustion, since, by the former, great strength is attained, and, by the latter, time is given for the complete combination of air with the beated fuel, for the transmission of heat through the metal, and for the escape of the steam through the water. The plates of the Cornish boiler are usually an inch thick, whereas those of a low pressure boiler are usually one fourth to five sixteenths of an inch thick; thus a much larger extent of surface is necessary to transmit a given quantity of heat in a given time in the former than in the latter case. The Cornish engineers allow seven times as much surface as in the general wagon boiler practice, for the evaporation of equal weights of water in equal times, and twelve times as much as in the locomotive; from which there is a gain of from 30 to 40 per cent. in the former, and of 64 with coke and 100 with coal in the latter case. The wagon boiler has great disadvantages of structure, being ill adapted to resist internal pressure, liable to collapse, and greatly affected by incrustation. According to the above table, which exhibits the mean of eight experiments, the combustion is 24 times more rapid per boiler, and 3 times more rapid per square foot of grate per hour, and the rate of evaporation is 7 times greater than in the Cornish. The loss of heat, the Cornish being unity, is 24 per cent. The construction of the locomotive boiler is so very different from that of every other species of evaporative vessel, that no strict analogy can be drawn betwixt it and any other. From the above practical results it appears, that the rate of combustion per boilor is nearly 7 times, and per square foot of grate per hour 23 times more rapid-that the rate of evaporation from equal surfaces 12 times more rapid than the Cornish boilerthe loss of heat, the Cornish being unity, 51 per cent. The author discusses at length the varying circumstances connected with different boilers, and the corresponding influence on the above results, and particularly the system of management by which he was enabled with a wagon boiler to approach the Cornish results. The table accompanying this paper will frequently enable the intelligent employer of a boiler to ascertain the best proportion of parts, and the best practice. For, having decided on the quantity of steam he requires, he knows the quantity of fuel which will generate it if he adopts the measures of surface and proportions of parts, which have given relative effects; or he can ascertain whether his present practice be good or defective. Notwithstanding the great stride which has been made in the economy of fuel by the Cornish engineers, the sources of waste are still great, and we may hope for great advances in evaporative economy, when combustion as a science and practical art has received the attention which it merits.-Trans. Ins. C. E. THE ARCHIMEDES STEAM VESSEL. Our readers will probably recollect that the Archimedes, a remarkably fine formed vessel of 230 (?) tons burden, fitted with a pair of engines, of 45 horse power each, manufactured by Messrs. Rennie, and the screw propeller, as applied by Mr. Smith, was first tried early last summer, and that the experiments were suspended, in consequence of the unfortunate bursting of one of the boilers. At that time the screw consisted of one whole turn of a single thread, 7 feet in diameter, and 8 feet pitch. The boilers have now been replaced by two new ones, manufactured by Messrs. Miller and Ravenhill; and at the same time a modification has been introduced in the form of the propeller. It consists now of two half turns of a thread, 5 feet 9 inches in diameter, and 10 feet pitch, placed diametrically opposite to each other on the propeller shaft, so as to occupy a space of only 5 feet in the length of the vessel. These alterations being completed, an experimental trip was made down the river to Gravesend, on Monday, the 4th ult., and the result was considered highly satisfactory. We regret that we were unable to be present, as we can, therefore, only speak from information we have collected since. We understand that she run from Gravesend to London bridge, a distance of 28 to 30 miles, which was accomplished in two hours, both wind and tide being favorable. No conclusion can, however, be drawn from this result, respecting the comparative performance, on account of the co-operation of the wind and tide; but the mean speed of the vessel through the water was ascertained during the trip, by noting the time in which she ran a mile, first with, and afterwards against the tide. The results of the experiment were the following:- Number of revolutions of the engine shaft per minute, The mean speed through the water was thus 4'32" 22 13.2 miles. 9'5" 23 6.6 miles. 9.9" The mean number of revolutions of the engine shaft was 221 per minute which, multiplied by 5 (which Mr. Smith informs us is the multiplying power of the wheel work, which communicates the motion from the engine shaft to the propeller), gives 120 for the number of revolutions of the screw per minute. If the screw were moving through a solid body, it would advance the length of its pitch in each revolution, or 1200 feet per minute, which is the same as 13.6 miles an hour; but since the vessel, and consequently also the screw only advanced at the rate of 9.9 miles an hour, there must have been a recession of the screw through the water, in the direction of the shaft, equal to 3.7 miles an hour. The proportion of the available power of the engines effectively employed in propelling the vessel was, therefore, 72.7 per cent., the remaining 27.3 per cent. being expended in obtaining the necessary resistance to the propeller. Mr. Hearapath, in his report in the Railway Magazine for the 19th Oc tober, has committed an error of 1.1 mile an hour to the disadvantage of the performance, in consequence of taking the mean time of running a mile, and finding the corresponding speed, instead of taking the mean of the speeds with and against the tide. We believe the latter to be the method usually followed; but, in case there may be any doubt as to its correctness, it is easily demonstrated thus. The speed with the tide is equal to the velocity of the vessel through the water (which is required to be determined,) added to the velocity of the tide which is an indeterminate quantity. Also the speed against the tide is equal to the velocity through the water, diminished by the velocity of the tide. If, therefore, we call the former V and the latter v, we shall have By adding these two quantities together, v is eliminated, and we find that the speed with the tide, added to the speed against the tide, is equal to twice the speed through the water.-Trans. Inst. C. E. In last No. of "Fulton," page 41, 26th line from top, for "1835," the date of the completion of the Erie Canal, read 1825. INSTITUTION OF CIVIL ENGINEERS. Feeling as we do, a deep interest in the formation of an American Society of Civil Engineers, we have always warmly seconded any endeavors to bring about a successful organization of the profession in this country. It has been with us a favorite topic, and in our intercourse with the meinbers of the profession, we have been frequently urged to move in the matter. During a tour through several neighboring States, we had received so many solicitations to represent the united opinion of a large number of Engineers, as to the necessity for a concert of action throughout the profession, an embodiment of the whole information on subjects connected with Civil Engineering, and a means of occasional but free inter-communication-the true and legitimate objects of a Society of Engineers-that we had resolv ed to give as far as it was in our power, a view of the desiderata for such an organization, with a proposed outline of a constitution, which should be in fact an adaptation of the constitution of the English Institute, to our more extensive country. It was urged that such a measure was necessary to the elevation of the professional standard in the United States; and that being in communication with a large number of Civil Engineers, we could more conveniently obtain an expression of their opinions. While taking the preliminary steps we, received intelligence of a meeting which proposed a convention for this very purpose. Of course we made no further move in the matter, than to publish the official proceedings of this convention and its committees. We must confess that a convention has always appeared a questionable mode of obtaining a satisfactory organization. Many individuals, who from various circumstances might be prevented from attending, and yet who entertained opinions from which valuable hints might be obtained, are thus excluded from taking a part in any organization which might take place, and would feel a natural indif ference towards making any further efort to introduce rules and regula tions which they might consider absolutely necessary. Besides this, the effort to connect with institutions already established immediately introduced feelings of party spirit, which should have no place in the formation of a society of Engineers, and which belonged only to those preexisting institutions. Many thought that the Civil Engineers of the United States, thus organized, would become in fact a mere section of some local society. These notions, whether incorrect or not, undoubtedly had an influence. We had hoped however, that these preliminary difficulties might be avoided, and the project prove successful. Such however, has not been the case. The official reports of proceedings have hitherto been published in this Journal, but although the result was known, we have not, until just now received the official announcement of the non-adoption of the proposed constitution, and consequent termination of all action. We give, (page 81,) a communication from Mr. Miller, with the final correspondence. From a perusal of them, we are satisfied that many of the gentlemen dissenting from the proposed constitution, are warmly in favor of an efficient organization, and would willingly unite on the common ground of the improvement of the profession. Before concluding, we must remark, that there appears to be a mistake as to some of the objects proposed. Although a library, and collection of maps, models, etc, are very desirable, yet at first they are not attainable and are not therefore to be made prime objects. A much more useful and far more practicable object, is to obtain a concentration of the influence and information of the profession, together with a concert of action. What we want first of all, is, an investigation into the improvement system, as modified by our peculiar circumstances in a national point of view; descriptions and details of individual works; statistics of works in operation; the elements of a judicious, economical and safe system of management of railroads, canals and steamboats, upon which subjects the opinion of an intelligent body of engineers would have the greatest weight, as a basis for legislative action when necessary, but which would go far to do away with any such necessity; and lastly the cultivation of science in all its bearings upon Civil Engineering, in which we doubt not, the members of the profession in the United States are fully able to co-operate with their transatlantic brethren. These are the ends to be kept in view, and yet to be accomplished with ease, if properly taken up. It is not necessary nor is it practicable that every member shall at any one time be in personal attendance although this occasionally is desirable and not difficult of execution. Members can appear by their communications and receive the benefit of all that is offered without personal attendance. We give place with great pleasure to the communication of Mr. Miller, and invite attention to the subject with the hope that we shall receive many ther communications on the subject, which we shall as cheerfully insert. |