ENGINEERING MAGAZINE, COMMENCED JANUARY, 1869, Published on the 15th of the month at $5.00 per year. The January number of this MAGAZINE, for the year 1881, begins the Twenty-fourth Volume. Beginning as an Eclectic Journal, and presenting almost exclusively matter selected from current literature, it literature, it has gradually become the chief medium through which the leading writers on engineering subjects can best present their original essays to American readers. The attitude of the MAGAZINE has been, and will continue to be, that of a journal of original and selected papers upon subjects relating to modern advanced Engineering. Theoretical and Practical Essays are alike presented in its pages, although the latter largely out-number the former, as best suited to the tastes and demands of the American Engineers. Some of the most valuable contributions to the literature of technical science within the last few years have been first presented in these pages. Among the more extended original contributions to the later volumes may be cited new contributions to Graphical Statics-Transmission of Power by Wire Ropes-Maximum Stresses in Framed Bridges-Momentum and Vis Viva-Rapid Methods of Laying out Gearing-Transmission of Power by Compressed Air-Geographica. Surveying— Mathematical Theory of Fluid Motion Thermodynamics - Practical Theory of Voussoir Arches-Cable Making for Suspension Bridges, &c., &c. To the above may be added the following valuable essays, translated from foreign sources, which have first appeared in these pages: Linkages and their ApplicationsThe Origin of Metallurgy-and The Theory of Ice Machines. The plans for future volumes comprehend many improvements in the same direction. The wants of the educated practical engineer, who desires to keep in the foremost rank of his profession will be steadily kept in view, and our constantly increasing resources for supplying the best of scientific information will be employed to secure such result. Cloth covers for Volumes I. to XXIII. inclusive, elegantly stamped in gilt, will be furnished by the publisher, for fifty cents each. If the back numbers be sent, the volumes will be bound neatly in black cloth and lettered, for seventy-five cents each. The expense of carriage must be borne by the subscriber. Notice to New Subscribers.-Persons commencing their subscriptions with the Twenty-fourth Volume (January, 1881), and who are desirous of possessing the work from its com. mencement, will be supplied with Volumes I. to XXIII. inclusive, neatly bound in cloth, for $60.00, in half morocco, $90.00. Notice to Clubs.-An extra copy will be supplied gratis to every Club of Five subscribers at $5.00 each, sent in one remittance. CONTENTS. PAGE. SMALL MOTIVE POWER. By Henry S. H. Shaw, Stud. Inst. C.E. I. (Illustrated)... From Selected Papers Inst. Civil Eng... 265 PNEUMATIC PROPELLER FOR RAILWAYS. By L. Gonin....From Abstracts of Inst. Civil Eng...... 279 By J. A. L. Waddell, C.E. NOTES ON RAILROADING. ON THE CALCULATION OF DIMENSIONS AS DEPENDING ON ON THE VARIOUS MODES OF TRANSMISSION OF POWER TO A Written for Van Nostrand's Magazine. 336 .. Paper read before Inst. Mech. Eng..... 339 PARAGRAPHS.-Note on the Present System of Permanent Way on the Six Chief Railways of France; Electric Properties of Paper, 280. Rousset's Deep Sea Sounder, 324. REPORTS OF ENGINEERING SOCIETIES.-American Society of Civil Engineers, 343; Boston Society of Civil Engineers; Polytechnic Club of the American Institute, 344. ENGINEERING NOTES.-On a Rope Tramway at Strasburg; Swiss Triangulation; The Suez Canal Tonnage, 346. IRON AND STEEL NOTES.-A Great Crucible Steel Casting, 346; Bessemer Steel in the United States; Chemical Society on Bar Iron, 347. RAILWAY NOTES.-Massachusetts Railroads; The Prussian Railway System: European Railway Commission, 347; Railways and Canals in Canada; French Railways, 348. ORDNANCE AND NAVAL.-An Hydraulic Ship: The Austrian Ironclad "Tegethoff." 348; The New Forty-three Ton Breech-Loading Gun, 349. BOOK NOTICES.-Publications Received; Locomotive Engineering and the Mechanism of Railways, by Zerah Colburn, 349; Caoutchouc : Gutta Percha et Gomme Factice; Nouveau Traite de Chimie Industrielle, Wagner et L. Gautier; Life History of Our Planet, by Wm. D. Gunning; Easy Lessons in Sanitary Science, by Joseph Wilson, M. D.; Materials and Construction, by Francis Campin, C. E.; The Steam Engine and its Inventors, by Robert L. Galloway; The Marine Mammals of the N. W. Coast of North America, by Charles M. Scammon; Sewing Machinery, by J. W. Urquhart, C.E., 350. MISCELLANEOUS.-Waterproof Paper-How Made, 350; Freight on Bycycles in England; Diurnal Variations of the Barometer; Circulation of Air in the St. Gothard Tunnel; Trade-marks Law in Switzerland; Color Relations of Metals, 351; Japanese Leather Paper; A Phosphor-Bronze Steam Launch; German Coal-owners ring, 352. VAN NOSTRAND'S ENGINEERING MAGAZINE. NO. CXLVIII-APRIL, 1881.-VOL. XXIV. SMALL MOTIVE POWER. By HENRY S. H. SHAW, Stud. Inst. C.E. From Selected Papers of the Institution of Civil Engineers. THE introduction of small motors has | been very extensive of late years, and is still increasing. The object of this paper is to consider, in a brief but systematic manner, the present state of the subject in this country, in order that a comparison may be formed of the relative advantages of the various agents now in use. In order to do this at all satisfactorily, an outline, at least, must be given of the modes of applying these agents for the purpose, and also the uses to which the motors themselves are put; so that, after a few preliminary definitions and remarks, the following method has been adopted: (I.) The working agents are classified, and the causes of loss by the transformation of energy on a small scale are briefly considered. (II.) The agents are taken in order, and the types of apparatus for applying them are dealt with and classified, and their efficiency examined. (III.) Finally, the relative advantages of the agents are considered, with reference to the various objects for which they are applied. ence, the difficulty of assigning an exact numerical limit exists, such a limit being after all quite arbitrary; for instance, a very small engine, driven at a considerable velocity by high-pressure steam, might develop as much power as an ordinary water wheel, or a much larger engine, under different conditions; but though the term in question would in. clude the first, it would commonly be held to exclude the two last; therefore, it will be interpreted as generally received by engineers, and will be taken to exclude locomotives and marine engines, factory and mill motors, but to embrace the large number of engines for what may be called auxiliary purposes, which are being made more and more to supersede muscular energy. The only direct sources of power at present used for small motors are fuel and a natural head of water, fuel including every kind of substance which by chemical action, rapid or slow, develops kinetic or actual energy. No source of power can be utilized without some loss of energy, and the "efficiency" of the apparatus used is the exact numerical It is difficult to define exactly what is value of the ratio of the useful work meant by Small Motive Power. Wheth- produced by it, to the energy expended er the size of the motor, the work per- upon it, by means of the working subformed in a given time, or the object for stance or agent; this quantity is, therewhich it is applied be taken for refer-fore, always some fraction less than VOL. XXIV.-No. 4-19. unity. Before the final application of the action of heat is caused to expand energy takes place, it may undergo a the agent, and thus to do work. Those number of transformations by means of marked (a) (a) (a) may be regarded as various agents, two or more being often merely transmitters of energy, and actemployed in the case of small motors-ing in the secondary way already referas, for instance, when steam power is red to. The respective efficiencies, of two used to produce an artificial head of of these, and also of steam, for this purwater or a current of electricity, which pose, have been dealt with in a paper by latter may produce work; but since the Mr. Robinson,* M. Inst. C. E., from resultant efficiency is the product of the which paper it appears that water stands fractions representing that of each in- the highest, but the loss of head, varytermediate piece of apparatus, the final ing inversely as the fifth power of the advantage to be gained must be bal- diameter of the transmitting pipe would anced against the loss necessarily en- cause its utility to diminish rapidly with tailed by the use of each extra agent. the size of the motor. It is only reThe same source of power may be ap-cently that electricity has been much plied to impart energy to motors by thought of for this purpose, or at any various agents and in different ways, rate has been practically applied, and and in order to avoid confusion, in stat- that agent is treated in Section II. aling the efficiency of an agent, the source most entirely with reference to this obof power should also be stated; thus, ject. taking gas as the source of power in the gas engine, and coal in the steam engine, the result of comparing these agents is very different to that obtained by taking coal as the source in both cases, and introducing as a factor in the former case the efficiency of the gas-making appara tus. The extent to which an agent is to be used may have much to do with determining its suitability for any purpose, and may considerably modify its application; indeed, the choice of the agent may depend on very different considerations, according as it is to be used on a large or a small scale. The importance of this will be shown hereafter, and leads to the agents applicable for use with small motors being more numerous than with large ones. SECTION I. Before proceeding to examine the efficiencies of the agents separately, it will be well to point out the losses of different kinds attending the transformation of energy, which are common to all. These take place, (1.) In dissipation, caused by the tendency of the agent to lose the energy imparted to it by communicating it to surrounding bodies, as, for instance, by conduction and radiation in the case of heat, and by leakage with a head of water. (2.) In the necessary rejection of energy due to the conditions of working. (3.) In the mechanical arrangements, in connection with which there are two principal losses, the one by friction, which is unavoidable, but may be reduced to a minimum by judicious design, the other by an improper supply of the agent, which supply may be either insufficient or excessive; in the former case the friction of the working parts absorbs an increasing proportion of the energy expended; in the latter the velocity of the motor increases, until the (a) resistances, both useful and prejudicial, are equal to the power applied to over(a) come them. (1.) The agents may be thus classified: Steam Heat engines. By direct chemical action (a) The agents classed under "heat engines" form the most important portion, and will be, to a certain extent, treated of together, a heat engine being regarded simply as an apparatus by which |