1842.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



39 



result is from a single experiment, and that we must not be deluded 

 by isolated trials ; but we are glad to hear that on the line where the 

 engine is now working, the Company have ordered an accurate record 

 of the performance, and quantity of fuel consumed during each trip, 

 which we hope will be made public. 



Mr. Stephenson has introduced tubes of wrought iron, instead of 

 brass or copper, in order that the increased heating surface might be 

 obtained without a corresponding augmentation in the price of the 

 engine. This he has not adopted without making several experi- 

 ments. During the last twelve montlis, he has had several boilers 

 working under his own eye with iron tubes, for the special purpose of 

 determining how far he could recommend them for general adoption. 

 The result has been all that he could desire; and it is owing in some 

 degree to this, that lie has introduced them with greater confidence. 



Having now described the modification in the boiler, we shall pro- 

 ceed to point out Mr. Stephenson's alterations in the mechanical 

 arrangement. In the ordinary engines, the mechanism for working 

 the slide valves is very liable to derangement, and considerable wear 

 and tear. This part of the engine he has so far simplified, as to 

 require only a simple connexion between the eccentrics and slide 

 valves, thus doing away with a considerable number of moving parts, 

 which have hitherto given rise to more casualties than any other part 

 of the ordinary engine. This is attained, by placing the slide valves 

 vertically on the sides of the cylinders, instead of on the top, as here- 

 tofore, so that the direction of the sliding motion of the valves, and the 

 central line of the valve rods, will intersect the central line of the main 

 axle, at the point where the eccentric is placed. In this case, the 

 eccentric rods are connected immediately to the prolongation of the 

 valve rods, without the usual intermediate levers and weigh bars ; 

 besides the slide valves of both cylinders are placed in one steam 

 chest, between the cylinders. 



Another iiuprovement is that ertected in the working of the feed 

 pumps : it consists in connecting the ]iuinp rods to the eccentrics 

 used for reversing the engine. By this arrangement, the velocity of 

 the moving part of the pump is greatly diminished, by which is secured 

 greater regularity of action. In addition to what we have already 

 described, there are several minor alterations, which we cannot fully 

 explain without giving detailed and elaborate drawings. 



The following are the principal dimensions of the engine now 

 working on the York and North Midland Railway : — 



Diameter of cylinder 14 inches. 



Length of stroke 20 



Diameter of driving wheels 5 J feet. 



Ditto of small ditto 3 



There are 150 tubes, giving a heating surface of "G5 

 Copper fire box, with a heating surface of . . 30 



Total heating surface 

 Length of boiler, Including fire and smoke boxes 

 Weight of the engine in working order 



795 feet, 

 ir feet. 

 15 tons. 



ON THE ORIGIN AND HISTORY OF THE OBLIQUE ARCH 



WITH SPIRAL JOINTS, AND THE VARIOUS SUBSTITUTES 



FOR IT. 



Mb. Editor — The interest taken by you in this subject is fully 

 evinced by your inserting in your journal of 1840 several papers by 

 the following authors: Edward Parry, C.E., Edinburgh; B. H. B., 

 Edinburgh ; (i. W. Buck, W. H. Barlow, Peter Nicholson; and in 

 l-jll by W. H. Barlow, I'eter Nicholson, and G. W., York; I there- 

 fore trust you will tind me a comer, being an original subscriber to 

 your very valuable journal, for some observations on the same 

 suljject. 



The following are the writers on the oblique arch in the order of 

 lime : — 



Rees' Cyclopedia, title. Oblique Arch, by William Chapman, 

 C.E. ; Encyclopedia Britanuica, On the Oblique Arch, by Thomas 

 Tredgold; Treatise ou Masonry and Stone-cutting, ISC^, by Peter 

 Nicholson ; Paper read before Literary, Scientific, and Mechanical 

 Institution of Newcastle, June, 1833, James Losli, Esq., Recorder of 

 Newcastle, in the Chair, (>n the Origin and Progress of Architecture, 

 and of the Arch in particular, and especially to sho»v that W. Chapman 

 was file inventor of the Oblique Arch — by Henry Glynn, Newcastle; 

 London and Edinburgh Philosophical Jounial, a paper on the con- 

 struction of Skew .\rches, by Charles Fox, April, l!?3ti ; ditto, March, 

 1S37 ; London and Edinburgh Philosophical Journal, A Letter from 

 Henry Welch, Xewcaslle, to Peter Nicholson, March, 1S37; Society 

 of Art*, Edinburgh, A Paper by Edward Sang, C.E., on Oblique 

 Arches, read Nov. Dec, iS3.'>, Jan. 1^30., and May, 1838 ; Treatise on 

 the construction of Oblique Arches, by James Hart, Mason, Weale, 

 1837 ; Essay on Oblique Bridges, by George Wutson Buck, July, 

 1S30 ; Treatise on the Oblique Arch, by I'eter Nicholson, published 

 in parts, part 1 published Jan., and part 2 in May, 1S39. 



The following are the facts, as brought forward in the paper of 

 Henry Glynn, claiming the honour of the invention for Mr. W. Chap- 

 man. In the article in Rees' Cyclopsriia, Mr. Chapman says " It 

 occurred to him" that each course of voui-^oirs should be rectangular 

 to the face of the arch, and their beds spii il, and their soffits curved 

 in that direction, and twisted in their sommering, and that the head 

 of each roit^soir in the acute angle of the bridge would make an 

 obtuse angle with its soffit decreasing towards the brim, whence it 

 becomes acute, and increasing as it approaches the other abutment. 

 The beds of the roussoirs are also twisted, and under equal widths of 

 bed, the space between the intrado and extr.ulo are increased upon 

 the face, as the haunches are approached (in the proportion as the 

 secant of their angle of deviation from a rectangle, with a line drawn 

 between each extremity of their soffit). The joint at the centre of the 

 arch is only rectangular from the face, the others diverging towards 

 the obtuse abutment, and increasing as the haunches are approached, 

 and converging towards the obtuse abutment. The development of 

 the face line of arch convex where acute with abutment, and concave 

 with the obtuse abutment. This curve he calls Polygonic, and the 

 convexity will depend upon the versed siue of the arch, and that the 

 form of arch to be preferred is the flat segment ; that the head of each 

 roussui'r on the acute angle makes an obtuse angle with its so8it, 

 decreasing as the crown is approached, thenceforward becoming 

 acute, and increasing as they approach the obtuse abutment. Finlay 

 Bridge near the town of Naas, over the Kildare Canal, a branch from 

 the Grand Canal, was erected by him in the year 17B7, on the above 

 principles. It is 25 feet span, with a rise of 54 feet, and the obliquity 

 is 51", or iU supplement 39". Mr. Chapniaii says "since the above 

 period the plan in a few instances has been followed; the same idea 

 may have occurred to others, although he never heard of it." Mr. C. 

 was a native of Whitby, Yorkshire, and practised extensively as an 

 engineer in Ireland, and died at Newcastle-on-Tyne, 1S32. He was a 

 member of the Uoyal Irish Academy, and of the Institute of Civil 

 Engineers, London. In the works of the writers ou this subject since 

 Chapman's time, no new principle has been developed, but only more 

 improved modes of working the arch stones; and none of the writers 

 notice Chapman, except Peter Nicholson, who tamely says, "He 

 seems entitled to the honour of originating the idea of oblique bridges 

 in their present form, but ho does not appear to have laid down any 

 sound principle by which it might be done ;" and even this brief 

 notice is suppressed in the second edition, and in many copies of the 

 first of Peter Nicholson's work. 



Previous to Chapman's bri<lge, all bridges of this description had 

 been built with the roiisioim laid parallel with the abutments, and 

 their ends bevilled olF in the <lircction of the roadway, and had been 

 carried by this means to an obliquity of \S^ from a right angle ; and for 

 others, where the obliquity wms greater, tho arch was turned square, 

 and the parapets curved in the direction of the roadway, leaving 

 alternate triangles outside them. 



The following bridges liave been built on Chapman's principle: — 



G 2 



