1S42.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



103 



An oblique bridge of a precisely similar design was erected by Mr. Cibbj, 

 the engineer, over tbc Croydon Kailway, near the Jolly Sailor station in 1838, 

 and I am informed that the peculiarities of the design were pointed out by 

 that gentleman to Mr. Woodbousc during an examination of tbc system of 

 longitudinal hearings adopted on tbc Croydon Kailway. 



Mr. ^Voodbouse wouhl doubtless verify this statement, as I am conviaced 

 he would be unwilling to profit by your correspondent's inadvertency. 



Feb. 23, 1842. Aletiiks. 



BLECHINGLY TUNNEL. 



Tins work, which is upon the line of the South Eastern and Dover Riil- 

 way, is now complcteil ; it is nearly three quarters of a mile in Ungth, and 

 is constructed ibrougb a hill forming part of the Wealden fiirmation uf geolo- 

 gists, consisiing of a blue clay marl, most remarkably distorted by an up- 

 fieaving force at some remote penod. which has caused the hill to be full of 

 faults, and occ.isiono<I considerable difficulty in ihc mining operations. In 

 the course of ibe work the fossil remains of ihc lijuanoilon and oiher reptiles 

 have been fonnd. The width of ihe tunnel in the clear is 24 feet, its height 

 21 feet above the level of the rails, with an invert having a versed line of 

 three feet : its figure is elliptical. The work was carrie<l on by means of 

 twelve wcjrking shafts of nine feet diameter, and progiesseil «iih e.\traordi- 

 nary if not unexampled rapidity, no Uss than 2ti4 yards having been befjan 

 and ccmpleted in one month. The bricks were all made on the spot, and 

 upwards of thirteen mil ions were made in the course of last summer, a con- 

 siderable quantity liaving been previously made and dried in flues during the 

 preee<ling winter. 



The greatest number of men employed at one time was .ibout 1,000. and 

 only two men lost their lives in tne course of the work, which casualties 

 arose from their own imprudence when using gunpowder. 



lk;iitxing conductors. 



SiK— I am about to put up an iron rod to a church tower as a lightning 

 conductor, and you would oblige me very much by informing me in your 

 next ('. E. Sf A. Journal, whether the hoMfasts may be iron also, or wheiher 

 they miisl ntcissarilii be of any other metal. I am not sure that if made of 

 iron they would not conduct the lightning to the masonry. 



Birmingham, Feb. 21, 1842. An Old Scbscbider. 



[We are averse to the use of iron for hold fasts, although they are generally 

 used for the purpose, if iron be used, we should recommend them to be of 

 caatMon, as being more durable than wrought iron; but we advise that a 

 supporter or holdfast be made either of glass, which can be cast very thick 

 for the purpose, or of slate slab, both non-conductors of electricity, and not 

 so liable to expand, or to be operated upoi by the changes of the weather as 

 metal— they can be let into the stone-work, and pinned in with cement. It 

 is very advisable to see that the end of the conducting rod is let into the 

 earth four or five feet. — Ed.] 



STEAM NAVIGATION. 



THE STEAM SHIP '• LITTLE WESTERN." 



AVf. have taken an opportunity of visiting this vessel, in order that we 

 might gratify our rcailers with a description of her machinery, which, nn 

 account of the l>eculiarity of its construction, and the reputed specil of the 

 vessel. h.as berome an object of considerable interest. The form of the vessel 

 resembles that of the fastest Gravesend steamers, but sharper at both ends ; 

 the paddle wheels are of Morgan's construction. The ribs of the vessel are 

 of T iron ; the exterior or shell is composed of plank about 4 inches thick, 

 'hie lioilers are of that description known as Splllers. Each boiler consists 

 of a large internal cb.amber, in which the fire is situated, and above the fire 

 several rows of brass tubes of about 2 inches in diameter are aiTanged in a 

 direction diflering by a few degrees from the horizontal line. The water is 

 contained uathin these tubes uhich communicate with a water space at each 

 end : the llame .and hot air circulate ouUiite uf the tubes, and the deflection 

 of thLMr direction from the horizontal line has the effect of maintaining a 

 constant current through each tube, thereby obviating tbc difficulty which 

 has Ijeen found u> at tact) to other tubular boilers, in which a pipe, if heate(I 

 in tbc middle, has been found to generate steam which expelli'ifthc water out 

 f)f each end, the elasticity of the steam preventing the water from .again 

 entering. 



The engines are by Messrs. Acraman 8c Co., of Bristol, of 80 horse power 

 each, an I the nature of their general arrangement may perhaps be more 

 clearly imagined by supposing a pair of eommoii land engines to be turned 

 upon their ends, that is, placed «llh the cylinder in a horizontal position, 

 the cylinder being beneath and the connecting ro<ls aljove. Upon tne keel- 

 sons of the ship the two cylinilers are laid horizontally with the usual space 

 between them, and from each side of each cylinder a column arises tosop|iort 

 the paddle shaft. The piston rod ii attached by straps to a beam supported 

 with rolumns in a vertical position, and from the upper extremity of tbc beam 

 the connecting rod extends to the crank. The coliinin which supinirls the 

 one eml ui the l«am centre is connecteil with the column which supports the 

 one end of the paildle or inlermc^liiite shaft with three strong turniil ninlle- 

 able iron .stays, by the means of which tbc requisite stability is obtained. 

 The inner end of each beam centre is prolonged sufficiently to support a short 



lever, and each of these two levers works an air pump Tlie two .lir l>ujnp« 

 therefore stand Ijetween the engines, at a distance Irom the line of the beam 

 centres equal to the length of the lev.rs. 



The piston rod works through both ends of the cylimler ; it is somewhat 

 larger than piston ro<ls for the same power usually are. is formed of br.-tss, 

 and is cast hollow. The steam and eduction valves are c iminon double-l>eat 

 valves of the same description as the expan.'^ion valves in common use. There 

 are two steam and two eduction valves, as is the usual prac.iie when spindle 

 valves are employed. These valves are wrought by an eccentric u|on the 

 intermediate shaft. The spindle of one valve does not pass through the 

 spindle of the other, but the whole four valves are arranged in a suit.ablo 

 rliest above the cylinder. 'Hie oi,era!ion of revers ng is arcompiishe<l not 

 by a loose eccen'ric. but by a double ended lever. The end uf the eccentric 

 rod, therefore, is made with two notches, and is maintained in the upper 

 notch when desired, by means of a little sliding guard or sheld. 



The air | nmps are of brass, and there is a m-arked peeularity in their con- 

 struction. Tbc air pump nistons. instead uf being provide<I with valves 

 through which the water and air ascend preparatory to their being expelled 

 (luring the asrendinf stroke, are made without valves, by which means the air 

 and water are to be exne led by the descendiug stroke. In ordii.ary air pumps 

 the pi.ston is a bucket, in the air pumps of these engines the piston is a plunger. 

 This species of arrangement Ins been previously tried, though with impertect 

 success. The air has been found to accumulate under the piunt'er. so that 

 when the plunger was drawn up. the air. by expanding, filled the intendnl 

 v,acuous space, thereby preventing an adequate quantity of water Irom enter- 

 ing the pump ch.amber from the condenser. The conse<juence of this defec- 

 tive action was an imperfect vacuum in the condenser, and consequently an 

 inadetpiate performance of the engine. 



The evil of the accumulation of air beneath the plunger.might probably be 

 correcteil by causing the plunger to travel past the port, the lower side of 

 the plunger being also made to slope downwards from the port. M'e are 

 informed that in the Little Western there is no provision of th i description, 

 or of any other for correcting this evil, and we have further been infunnetl 

 that without any such corrective appliance, the evil is foun 1 to be inopera- 

 tive or inexistcnt. We confess we are unable to resolve this apparent incon- 

 sistency. 



The advantages of the mode of construction of tlie air-pump pistons uhich 

 Messrs. Acraman have adopted are eminent and manifold, and that any accu- 

 mulation of air Iwneath the piston may be prevented by a pru[>er arrange- 

 ment we are thoroughly convinced. The greater par; of the noise the work- 

 ing of an engine occasions, arises from the action ol Ihe valves in connection 

 with the air pump, .and there is much leakage often through tliem, and much 

 wear and tear. Messrs. Acraman's .arrangement will go far to prevent this, 

 and the benefits of the system would be materially enhanced, if the action 

 proper to the foot and delivery yalves were accomplished by Ihe agency of a 

 simple form of slide valve. There would then be no noise at all. and the 

 vacuum in the condenser would probably be something better than in ordinary 

 engines ; for in ordinary engines there must always beaililTerence of pressure 

 between the iiir pump and condenser sufficient, with the difference of the 

 level of the water to ojien the foot valve. The best engineers, by placing 

 their foot valves nearly perpendicular, r nder the difference of pressure 

 lietween the vapour in the condenser and that in the air-pump barrel, very 

 inconsiderable, yet there is a difl'erencc in all ordinary engines, and this 

 dilTerence would be extinguished by discarding the foot and delivery valves 

 in favour of a slide valve, which would accomplish the work of b ith. 



The workmanship of the engines is very superior. There are no nist joints, 

 but all the surf.aces intended to be filled are planed and made tight by a little 

 re<l lead ; there is no gasket joint between the cylinder and nfbnder cover, 

 but both surfaces are made quite true, and then a little red lead renders them 

 perfectly tiglit. There are many .advantages in this mode of fitting which 

 we are linppy to find is now ailopled by the most eminent of our engineers. 

 The pressure of steam in the boiler is 6J lbs. Ilie sjieed of the vessel is 

 about the same as that of Ihe H>lipse, Railway, and Blackwall. 



The Little Western is certainly a favourable example of the skill of Bristol 

 mech.anici.ans. but that there is anything either in the stnieluro of the hull 

 or machinery pre-eminently excellent, we utterly deny. In the production 

 of the vefsel there appears to have been loo great a straining afier novelty 

 and there are evidences of a disposition to select arrangements, not so much 

 by the consideration of what is excel enl as of what is unu.sual. 



The following are some of Ihe proi«rlions of the ves.sel and engines; she 

 is 721 tons, measures between |<rpendiculais 200 ft., over all 216 It., krrl 

 VJ'y ft., breadth of beam 27 ft., ami including pa Idle boxes 47 feel, leng h of 

 saloon 41 ft. by 24 ll, wide, ladies' cabin 20 lu lung. 



The Eail India Company's Steam-frigate Memnon. — On Tuesday, 22nd ult, 



Ibis splendid ve.s.sel, uf 1,100 tons burden, mounting two C4-|Kiunders. and 

 four 32-poiiniIer guns, ami having ibem and .all brr shot on board, with 

 al>iut 300 tons ol eonls. and a heavy ear^ro sufficient to test her cnpal.ihtles 

 for a long voyage, left her moorings .at Blackwall, and nroree<led down Ibe 

 river in excellent style, lor the luirpose of ascertaining the efficiency of b«r 

 engines and sailing qualities. 'The Memnon w.as built by Mr. Kletcher, and 

 the engines, of 4()U-lior5c power, were conslnirted by Messrs Msudslay. 

 Sons, and Kielil, with copiier boilers. The cylinders are double, the a team 

 can be used expansively, and the consumption of fuel rej.ulaled to suit anjr 

 circumstance of slow or quick sailing; she has also disconnecting gear to 

 work one wheel without the other, if found nee ssary. On arriving at Long- 

 reach Ihe lull power of ihe steam was applied, an-l the engines workad 

 beautifully, the vibration lieliig scarcely perceptible; the large wherli, 28 

 feet in diameter, entered the waier with such elfect as In pnq el the veutl. 



nth her heavy cargo, at the rateuf 11) miles per hour, affording the greatest 

 .atisfaction to her commander. Captain Powell, ami all the gentlemen 

 pnseiit. She proc.'ciled as far as ."^heemess before returniiiu; the mat 

 and simplicity with which Ibe disconnecting gear (Mr. Field's patent) 



manner 

 re- 



