18 J.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



41 



SETTING OUT RAILWAY CURVES. 



Sir — The following mode of setting out curves, by means of equal 

 chords and ordinates, which I have successfully practised, is bolh accurate 

 and easy of being applied : — 



Fig. 1. 



Let B and D be the ends of two straight lines, tangents to the cnrve 

 BCD, which we wish to set out — the position of the two lines having 

 been correctly determined from the base line of the survey. We must 

 then ascertain the an^le that a cliord of any convenient lengtli (say 10 

 chains) malies with the tangent A U ; which having found, the intermediate 

 ]>oiut3 on the curve are fixed l)y oflsets from the chord. The radius being 

 known, and the length of the chord determined, the following formula will 

 enable us to fiad the angles of chord and tangent : 



Radius .' i chord ; ; 1 ." sin J the arc. 

 Therefore, sin J the arc = chord. 



2 radius. 

 Thus, if chord =: 10 chains, and radius = GO chains, 

 sin 4 arc =: ^ = Vj = -0333' = nat sine 4° 47'. 

 To find the offsets, the line F G which bisects the chord is at right 

 angles with it. G H, which is a tangent to the curve, is also at right 

 angles with F G. tr H and I C are, therefore, parallel. If H C be drawn 

 at right angles with 1 G, it will be parallel to I G, and also equal to it ; 

 and G H = T C = 5 chains. 



HC = FG— ^t^ 

 bd = F G — ^F& 

 ac = FG 



■ GH2 



■ G fc- ; and 

 ■v^F G2— Ga2. 

 The parallel lines, H C, */, ae, and G I, are all equal. 



Therefore,d/=HC — id; ce = HC — ac, &c.; and GI = HC. 



The formula ^^ „ will give a very near approximation to the distance 



of the tangent from the curve, and might be taken as the olfset without 



Gb- 



G3 = 



producing any appreciable error; avn "'" 8^^* *"* > ^°*^ oFT = ""^i ^*- 



Fig. : 



In the case where a building or other obstacle may intervene, at B, (fig. 

 2) to prevent the setting up of a theodolite ; if from A we set oflT the dis- 

 tance A a' equal to h b', we shall have the direction of a chord, ba, of 10 

 cbains ; by means of which we can determine the direction of a new 

 chord, b c. 



Carmartbeo, Jan. 3, 184*. Z. 



Sir — I had no intention to excite the ire of your correspondent, " An 

 Engineer out of Employment." He has evidently mistaken my meaning. 

 I shall leave him, therefore, to cool on it. 



A specific chord line, it is well known, presupposes two points, already- 

 determined in a curve. The first, or starting point, can be attended with 

 no difficulty ; but the other, though easily found, or assumed, on paper, 

 is not always so readily found on tlie ground: and when obtained, or given, 

 on the ground, it must be sf.f.n from Ibe other point in order to be of any 

 use. " To find it out," as your correspondent says, " by the aid of a com- 

 mon theodolite," would be an enilless affair — even if the surveyor knew 

 how to set about it. The time occupied in his doing so might certainly 

 be employed to more advantge, I miy say, by amj other mode of tracing a 

 curve- — even by " building," as your correspondent calls it ! — apropns, my 

 instrument does not, by any meaus, limit the length of the tangent : it may 

 be either lengthened or shortened, according to local or other circum- 

 stances. 



Military Library, 30, Charing-cross. W. Tait. 



SAFETY OF RAILWAYS. 



(Extract from a Report made to the Blinister of Public Work-s in France, by M. DE 

 BOUREUILLE, head of the Railivay Department.) Translatedfor the ' London Jourual." 



The Special Commission, charged by the Minister of Public Works to 

 inquire into the questions relating to the security of transit upon railways 

 has, from the first, had two subjects of very different natures to consider. 

 The catastrophe of the 8th May, 1842, had called public attention most 

 particularly to the construction of axles of locomotive engines and carriages, 

 and to the terrible consequences of the shocks to which passenger trains 

 might he exposed upon railways. 



The safety of railway transit may depend on various circumstances • 

 1st, — On the state of the road or way, and the mode of its construction • 

 2ndly, — On the state of the materials employed, viz., the engines and car- 

 riages, and the diflerent parts of which they are composed, viz., the wheels 

 axles, springs, &c.; 3rdly, — On the formation of the trains — that is to say, 

 the mode of attaching the engines and carriages together, the kind of brake 

 employed, the methods of deadening shocks, i:c. ; 4thly, — Ou the refula- 

 tions to be observed when the trains are running, the speed at which they 

 are to travel, the signals and means of communication established either 

 between the engine-drivers, or between them and the ofli( iais at the sta- 

 tions or on the road ; Sthly and lastly,— On the degree of intelligence em- 

 ployed in the service, and the ability and characters of the persons em- 

 ployed. 



1. On the Railway and its Accessaries, such as Crossings and Changes 

 ill the direction of the Road. 



It will be unnecessary here to recapitulate the various plans which have 

 been successively employed for the construction of railways: it will be 

 sufficient to observe that the method now generally adopted in France con- 

 sists in fixing the rails by means of wooden chairs placed in cast iron bear- 

 ings, which are fixed two together upon wooden sleepers, placed at equal 

 distances apart : the number of sleepers varies according to the nature of 

 the soil upon which the road is to be formed, the weight of the rails &c. 

 The sleepers are covered with sand to keep them in their proper position. 



Some engineers, in order to render the rails more firm, and to prevent 

 their beading between the transverse sleepers, have proposed to lay the 

 rails upon longitudinal sleepers. The line of rail from London to Bristol 

 is laid down in this manner; but it is not apparent that this plan has been 

 much followed iu France. 



The Commission bad therefore to inquire, on the one hand, whether this 

 method of constructing railways was sufficient to maintain the rails at the 

 required distance. This was answered affirmatively, adding, however, 

 that it would be advisable to place the sleepers nearer'together at the junc- 

 tion of two lines of rail, than at the intermediate points. As a corollary 

 to this question, Ihe C'ommissiou inquired whether the breadth between the 

 rails most commonly adopted, viz., 4 ft. 8 in., was sufficient, and whether 

 it would not be advisable to increase it. On the first poiut, the answer in 

 the affirmative was given without hesitation ; and, as to the width of road 

 the Commission was of opinion, that the gauge at present in use n)i"ht be 

 continued ; adding, however, tfiat it would be advisable to keep it in tun- 

 nels, and between the parapets of works, the same as on levels and in cut- 

 tings. 



With regard to any alterations to be made in the position and form of the 

 road, the Commission declares, that the depression or elevation of the 

 rails, a defect in fixing them in the chairs, derangement of the sleepers 

 supporting them, inequality in the sand forming the foundation of Ihe road 

 or too thin a layer of this sand, must be considered as very likely causes 

 for the carriages getting oil' the rails. The Commission mentions two other 

 causes of the rails getting out of order, v hich seem to be quite as danger- 

 ous : — First, the displacement of the rails iu a longitudinal direction or 

 direction of movement ; and secondly, the uniform inclination of the 

 sleepers supporting the chairs aud the consequent displacement of the 

 rails. These various causes of danger may be averted, or at least greatly 

 modified, by a constant aud attentive surveillance of the road. 



The Commission had still to examine, on the one hand, whether the form 

 adopted for the rails was the most suitable; and on the other hand, whether 

 the test of the manufacture of the rails, before employing them, was suffi- 

 cient to be relied upon. 



