m 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[February, 



Sir — I have subscribed to your periodical from its oommeiicement, 

 and receivpd from it much pleasure and useful information. I have been 

 still more gratified of late with the increase of space devoted to my 

 favourite study, mechanics, and it is to a paper of tliis nature in your 

 January number, that I wish at present to direct your attention. A 

 correspondent of the name of John Charles Pearce describes, at con- 

 siderable length, a contrivance for reversing a steam-engine with one 

 eccentric as an invention of his own, althougli it has long been quite 

 common in this country. I may mention, as an example, a high- 

 pressure engine of about 20 horse power, built for some experiments 

 with a canal boat on the Fortli and Clyde Canal, and afterwards 

 altered as a pumping-engine for a dry dock at Grangemoutli, in which 

 the identical contrivance was applied successfully. 



I am, 



Gla'>gow, Your constant reader, 



ilM Jan. 1841. Ax Apprentice. 



Sir — If I am trespassing too mucli on your columns by thus a second time 

 reijuesting the favour of a jjlace therein, I heg you will suppress, curtail, or 

 defer, as you think best, the following remarks which I am induced to send 

 you after the penisal of a coinmimication fiom Mr. John Charles Pearce, in- 

 serted in your number for the present month. 



Mr. J. C. Pearce is correct in bis observation as to the possibility of work- 

 ing Locomotive Engines by two fixed oocentrics, but he overlooks an objection 

 to this system which, with your jierniission, I will take the liberty to point 

 out : jirevious however to entering upon the objection, it will be proper to 

 explain a few conditions, which are i.ispparable from this system of two fixed 

 eccentrics, and in one of which, originates the above mentioned objection. 



No. 1. The eccentric must precede the crank in its action, when the engine 

 is going forward, otherwise no lead can be given without a complication of 

 levers ; a slight objection was made to this, inasmuch that for going forward, 

 the eccentric rod must work the upper pin of the double lever of the valve 

 motion, and must be held in gear ,_ so that should any thing get wrong in the 

 hand motion, the eccentric rod would fall out of gear, and would thus reverse 

 the engine. 



No. 2. The crank being placed in a horizontal position, so that the piston 

 may be at oi;e ciul of the cylinder, the eccentric must be placed exactly per- 

 pendicular to Mr. J. C. Pearce 's line C E, which is a straight line drawn 

 through the centre of the crank shaft, and the lever spindle of the valve mo- 

 tion. 



No. 3. The amount of lead depends upon the length of the eccentric rod. 

 The shorter this rod is the greater will be the lead. 



No. 4. The lead being determined by the length of this rod must remain 

 invariable imless you move the eccentric on the axle, in which case you in- 

 crease the amount of the lead one way, iut you diminish it for the reverse 

 motion. 



This last circumstance has been deemed objectionable, because with vary- 

 ing loads and s]ieed, it is desirable to have the power of augmenting or 

 diminishing the amount of the lead. 



Several engines are at work on the Paris and St. Germain railway fitted 

 each with two fixed eccentrics, upon the principle laid down by Mr. J. C. 

 Pearce, and for which a patent was obtained in Paris, I believe in 18.38. 

 They work well, hut in consequence of the above mentioned inconveniences 

 are being fitted with four eccentrics. 



I have had several opportunities of comparing the duty done by these en- 

 gines with that of others having four eccentrics, and at work on the same 

 line, and have found very little difference in their results. I have reason to 

 believe that the determination to alter them, originated more than from any 

 other cause, in the desire of the Company to assimilate all their engines, by 

 adopting one uniform system of eccentric motion ; it is proper here to observe 

 that the eccentric rods of these engines were originally made too long, and 

 did not give sufficient lead to the valves, that in consequence tliereof, the 

 eccentrics were advanced a little on the shaft, so as to give tlie required lead 

 for gouig forward, and the engines were /Ah* rendered slow the lack way. 



Tlic same Company fitted a p.iir of fixed eccentrics to another engine, pay- 

 ing proper attention to the length of the eccentric rods in order to obtain the 

 required lead both ways ; the eccentric rods were in tiiis instance so short, as 

 to work with a disagreeable motion, because the suspension pin of the hand 

 lever motion, which in consequence of the shortness of the eccentric rods was 

 attached to thcni, comparatively nearer than usual to the eccentric, occa- 

 sioned an up and down motion of the fork upon the pin of the lever of the 

 valve motion, which made it requisite to make the parallel clutch of the fork 

 much deeper than usual, to prevent it from fiying out of gear ; this might, it 

 is true, have been easily remedied, but the Company not being willing to 

 make any further outlay in experiments, and desirous to have their engine, 

 replaced the whole affair by four eccentrics. 



The nmst serious objection made to the two fixed eccentrics, in my opinion, 

 rests on the impossibility of varying the lead of the valves both ways. 



The original plan adopted of two moveable eccentrics is a verv good one, 

 because if any thing gets out of order with the motion, you can always work 

 home by hand. The main objections are, their expcnce,' and the diffi'cultv of 

 getting them sufficiently strong. 



The four eccentrics act perfectly wfcll, but render the valve motion so very 

 crowded, as to be frequently inconvenient. 



A very ingenious method has been proposed and executed by Messrs. 

 Hawthorn, brothers, of Newcastle-upon-Tyne, for replacing tlic eccentrics al- 

 together, by a motion taken from the body of the connecting rods; the lead 

 has been very cleverly determined by these gentlemen ; the same objection 

 however exist as t o the difBculty of varying the lead, which could only be 

 removed by complicating the motion. I have seen an engine of this descriij. 

 tion at work and giving satisfaction. 



I rcn)ain, Sir, vour verv humble servant, 



H. E. 



London, January 16, 1841. 



PROCEEDINGS OF SCIENTIFIC SOCIETIES. 



ROYAL INSTITUTE OF BRITISH ARCHITECTS. 



Jan. 11. — J. B. P.\pwoRTH, Esq., in the Chair. 



A paper was read by Mr. E. I'.inson, Jun., Fellow, comparing the Campa- 

 nili of the lower ages in Italy, with those of the Norman period in England. 

 The matter of Mr. I'Anson's discoiu-se went to illustrate that highly interesting 

 subject, the spread of the Romanesque style of architecture, and the modi- 

 fications it undeiwent in its progress. 



Jan. 25. — H. E. KEXDAf.i., Esq., in the Chair. 



.\ paper was read on the Construction of the Reservoirs from which Venice 

 is supplied with fresh water, by C. Parker, Fellow. This city being dependant 

 on the clouds for a supply of this most necessarj- element, means are provided 

 for collecting the rain water in immense tanks, which it enters by filtration 

 through beds of sand, the means by which natural resen'oirs are fitted, and 

 their contents purified, being in fact imitated by art. The mode of con- 

 structing and puddUng these tanks was described in detail, and illustrated by 

 plans and sections. 



An .\rtesian well lately constructed at the Surrey County Lunatic Asylum, 

 was described by Mr. S. Lapedge, Associate, and a section exhibited of the 

 strata through which the borer has passed, to the depth of 347 feet. The 

 water rises from a bed of dark sand to within 30 feet of the surface, and a 

 well 190 feet deep forms a reservoir, wluch constantly affords a supply suffi- 

 cient for the purposes of the establishment. 



A drawing was presented and a discussion read of a timber bridge erected 

 at Hulne Park, by Mr. Barnfather, architect. It is an arch of 100 feet span 

 and 5 feet rise, constructed of balks of timber raised to a curve by means of 

 iron wedges, and remarkable for the simplicity and economy of construction. 

 This principle was introducted from America about 25 years ago. 



The Secretary for foreign correspondence, Mr. Donaldson, read a communi- 

 cation from Baron Gasparin, President of the Comite Historique des Arts et 

 Monumens, at Paris, accoinpanj-ing a donation of the bulletins (or reports) 

 of the committee. 



SOCIETY OF ARTS FOR SCOTLAND. 

 Sec. 14, 1840.— Dr. Fvfe, President, in the Chair. 



Mr. Galbraith read a jiaper on Trii/onometrical l^velliiig, and on the effects 

 of a supposed local attraction at the Calton Hill, Edinburgh. In the first 

 part of the pa])cr he detailed a number of observations which be had made 

 for the purpose of determining the amount of atmospherical refraction, and 

 described a formtda for its computation considerably simpler than that in use. 

 In the second part of bis paper he detailed a series of observations for the 

 purpose of determining the latitude of the observatory of Ediidmrgb, to which 

 he bad been led by a known discrepancy between the latitude determined by 

 Professor Henderson, from observations made by the mural circle, and the 

 latitude found from the observations made on Kelly Law, in Fife, by help of 

 the Ordnance zenith sector. It having occurred to him that the rising of 

 the countrj' to the sotithward of the Calton Hill, and the slope northward to 

 the Firth of Fortli, may cause a local distiu'bance of the plumb line, he re- 

 solved on deducing the latitude of tlie Observatory from observations made 

 on Inchkeith, in the middle of the Firth, where the local attractions may be 

 expected to be balanced. The determination of the latitude of Inchkeith 

 Light-house agreed within half n second with that found by the Ordnance 

 surveyors, but differed by .seven seconds from that deduced by transference 

 from the Observatory. f)n this account the author conceived that tlic pro- 

 bability of the existence of a local attraction at the Calton Hill was strength- 

 ened. The paper was ordered to be printed. 



Mr. Alexander exhibited a workim/ model of the Electric Telegraph, 

 having premised that the model was intended merely to illustrate elementary 

 principles. This instrument contained a separate wire for each distinct sig- 

 nal : the exhibition of it gave rise to an interesting conversation, in which 

 a number of the members took part. Mr. Ponton adverted to the modi- 

 fieation which he had exhibited two years ago to the society, in which a 

 suflicient number of signals were obtained by the use of three Hires oHly ; he 

 also mentioned that during the exhibition in the Assembly rooms, he had 

 openly talked of a method of reducing the number of wires to two, by intro- 



