102 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[March, 



" Ol' MOMENTUM AS A MEASURE OF THE KFKKCT OK LOCOMOTIVE 

 ENGINES. 



" Tlie cfl'ectivc power of a locoiuotivc engine — l)y which is meant (lie ex- 

 cess of power after overcoming its proper friction, and llie resistance from 

 Jlie lilast — is solely expended in the generation of nnnncntnm. The momen- 

 tum communicated to tlie cidire mass set in nnUimi represents the nsefnl 

 mechanical effort exerted liy the steam; this clfect of tlie engine is, there- 

 fore, at all limes delerndnahle ; for, licing the simple prodnct of the mass 

 moved, nudliplied into its velocity, it is the prodnct of two ipianlities easily 

 ascestained nnder all the practical drcnmslances of railway trattic. The con- 

 sumption of jjower, as water in the shape of steam, is a third (juantity also 

 readily apiireciahle. 



" Were it pussihlc to work a locomotive engine and its train ik vacuo, on a 

 truly lc\cl plane, the momentum generated hy au cfpial exjienditure of power 

 woidil ho a constant (|nantity at all velocities; for, the resistance hcing in- 

 \arialilc, ecpial momenta would he produced liyan ennal expenditure of i)owcr 

 with all loads, as the velocity attained would he in the inverse ratio of the 

 loads, ami vice versa. This hypothetical case sii]iposes friction and resist- 

 ance of all kinds to he constant." 



Tills is not only a new l/ituri/ of the locomotive eiigini', but one 

 vvliich involves a new dejinition of the word momtntam ; tor, according 

 to the |ircsent acceptation of the term, nionicntmn can only be gtiie- 

 )•((/£(/ during an acceleration of (he moving mass, which accelleration 

 is not, and ouglit not to be considered in locomotives, nnless the time, 

 in vvliich a given accession of velocity is also taken into account at 

 the same time, which is evidently not contemplated by Mr Parkes. 

 What is here understood by the mominliim gtinraled in one second, is 

 nothing but the absoliilt momentum referred to the second, as the unity 

 of time, which is deduced from the uniform velucitij of the engine, 

 williout reference to the time in which it acquired that velocity. 



Since the resistance does not enter into this expression of the power- 

 of the engine, it would follow tliat the same engine would draw the same 

 train at the same velocity, whatever the nature of the road may be ; 

 since the evaporation being the same, the ])owcr expended must be 

 the same ; and since tlie mass moved is the same, so must also its 

 velocity, to make its momentum ecjual. The absurdity of this doc- 

 trine is obvious. 



Tlie next section contains some good observations on Ihe blast, as 

 well as some experiments made by tlie author on the resintance jiro- 

 cliiced hy it; but no reliance can be placed in the results tiiere re- 

 corded, some of them being evidently impossible. At page 147 we 

 read the following: 



" The immediate cause of my entering on these experiments is worth men- 

 tioning. I one day oliscrved tlic mechanic in care of the machine, wliilst 

 pre|iaring for work, opening and shutting the grease cocks of a cylinder, and 

 giving oil to a jiiston. The engines were then working without load, and it 

 was evident that a small vacuum existed after the blast, or the oil would have 

 been blown hack instead of entering the cylinder. This fact, the possibiUty 

 of which had not before struck me, induced me forthwith to order another 

 gauge from Mr, Adie, which v^as fixed on one of the blast-pipes, in a con- 

 venient place for constant observation, about 2 J feet from its junction with 

 the cylinder, the bnlh being exposed to the full current of the escaping steam. 

 This instrument detected the fact of a vacuum by marking, usually, a teni- 

 pcralnre of from 208" to 210", or al)out 1 lb. per square inch below the at- 

 mospheric pressure, the active steam on the piston being 1 J lb. above it. 

 When the engine was driven at double velocity, or at 120 revolutions per 

 minute, at which speed it reipiired about Z\ lbs. of steam, the thermometer 

 rose to 211°, and when locomotion was given to the machine at the usual 

 velocity of 00 revolutions of the crank shaft, and rcijuiring 4 llis. in the 

 lidilcr, the blast thermometer stood at 212 , exhibiting a pressure equal to 

 the atmosphere only. At 8 lbs. on the piston, a couider pressure of about 

 2 Ills, was cxhibitecl, at 15 lbs., about 4 lbs., and at 20 lbs. the blast thermo- 

 meter indicated G lbs., bejond which point I was unable to load the engines." 



In his observations on M. de Pambour's experiments (page 87), Mr. 

 Parkos justly remarked that a racuum on t)ie opposite side of the 

 piston was an impossible result, and this remark evidently holds 

 good for his own experiments as well as liis deduction from those of 

 M. de Pambour. 



In conclusion, we would again caution our readers against adopting 

 the conclusions arrived at by liy Mr. Parkes without first submitting 

 the whole of his work to the strictest scrutiny. There is some, and 

 there may be much good in it ; but, having detected errors of 

 importance in some parts, we cannot depend on the correctness of 

 that which we liave not had time to inquire into. 



N'ery great merit is however due to Mr. Parkes for the indefati- 

 gable zeal he has exhibited in the compilation of data, and in the 

 comparison of results therefrom deduced, which must have cost him 

 much time and labour, with the praiseworthy object of advancing our 

 yet imperfect knowledge of the eft'ects ancl comparative economy of 

 steam engines. 



The Uoval Lodges in Windsor Gre.vt Park, from Drau-iiiijH by 

 II. 15. ZiEGLER, executed hy L. Hague, /« lllhoyropliy, liy e.rjjrcsi- command, 

 for Her Gracious Majesty Queen Victoria. Folio. Ackermann. 



Ifhy "express command" we arc to understand more than a mere per- 

 mission, all we can say is that we caiiuot possibly conipUnient " Her Gracious 

 Majesty" upon her taste, for while considered as drawings, the plates are far 

 from rivalling preceding specimens of Uthography, ,as architectural subjects 

 they arc very much mure unsatisfactory. Indeed it seems to have been taken 

 for granted that the less that was said about these buildings the better, there 

 being no description or information of any sort attached to the jilates ; there- 

 fore, not happening to be acquainted with their history, wc are unable to say 

 who was the perpetrator of these Cockney whims and monstrosities — taste- 

 less jumbles of cottage, castle, and what not, without a single redeeming 

 merit of any kmd, dow aright paltriness, and utter want of feeling for any one 

 of the styles thus attempted, being their chief characteristics. 



Scarcely can we bring ourselves to believe that Sir Jelfry M'yatville was 

 concerned in the erection of this architectural tnunpcry ; and if not, he would 

 do well to clear himself from a suspicion which is very likely to attach itself 

 to him, as the Royal architect at Windsor. Let the designs have been by 

 whomever they may, they ought never to have been executed ; and it fills us 

 with concern to behold — emanating from what ought lobe the fountain head 

 of taste, such specimens of it as would he excusable only in some suburban 

 tea-garden. But for their feebleness they might pass for arrant caricatures. 



Arboretum et Fruticelnm Britannicum ; or, the Trees and Shrubs o/ 

 England. By J. C. Loudon, F.L. and H.S., &c. London: Long- 

 man and Co., 1S39, 8 vols. Svo. 



The name of Mr. Loudon suggests the idea of a work of great ex- 

 tent, of great labour and research, but that now before us surpasses 

 any of his previous triumphs. It bears less the impress of an indivi- 

 dual production than of a national work, a character sustained by the 

 number and value of its contributors, and by the eagerness with winch 

 all ranks devoted themselves to the promotion of a task so noble. The 

 man of science hastened to contribute from his stores of knowledge, 

 the grandee and the gentleman threw open their rich collections, or 

 volunteered at their own expence to obtain illustrations for the work. 

 From the duke downwards every jiatron and amateur of horticultural 

 science seems to liave considered co-operation in the work a lUily and 

 a iileasure. This detracts not from the value of Mr. Loudon's labours, 

 it enhances them, and is a high proof of the estimation in which they 

 are held. 



This work, as it professes, gives a pictorial and botanical delineation, 

 and scientific and popular description of the native and foreign, hardy 

 and half-hardy trees and shrubs of England, with their propagation, 

 culture and management, and their a))plication in landscape gardening. 

 To Ihe landscape artist trees have the same importance as details of 

 style have to the architect, and every artist and amateur is, cinise- 

 quently under an obligation to possess himself of this cncyclopjrdia of 

 the art. The letler-))rcss in the old times nnglit legitimately have 

 been spun out to twenty volumes; the engravings our fathers could 

 never have compassed, they are two thousand five hundretl in number, 

 and are executed from drawings by the Sowcrbys, and other botanists 

 of distinction. Wc have only one fault to lind w ith the work, and 

 that is, that wc see it disfigured with a barbarous Latin name. 



To give extracts from these volumes would be indeed to realize 

 the old Greek aiiophthegm of showing a brick for a house, so that we 

 must content ourselves with expressing our feeling of the value of Mr. 

 Loudon's labours, and with recommending this admirable work to all 

 who wish to follow with success an art so graml, as that of landscape 

 gardening. 



Elementary Principles of Carpentry, illustrated by 50 engravings and 

 several mod-cuts. By Tho.mas TuEDGOLn. Third edition, with an 

 Appendix, by PiiTEU Bahlow, F.H.S. London : John Wcale, ISIO. 



Tins is a new and improved edition of Tredgold's work, and Jlr. 

 Bariow bases his chief claim for its value as much on the proper re- 

 tention of the original matter, as on the excellent additions which he 

 has appended to it. These accessions are so important as to make 

 the new edition desirable even to those who possess the work in its 

 original form. Among many excellent specimens of Foreign and 



EnglisU rooling «ow introtluced ftom tlie liigUest sywees, inay be pat" 



