1842.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



331 



riage down to the axletree. The gauge may be tluis increased from 4 ft. 8A in. 

 (0 C ft. 2 in. — thus arguing for an increased breadth, that the centre of 

 gravity may be lowered, and the diameter of the wheels thereby reducing 

 the friction, and increasing the power, to overcome the "surface resistance." 

 This is, in other words, getting more leverage ; but such an advantage, how- 

 ever, does not apply so much to rail" ays as to common ruads, for. on the 

 railway, there is little or no obstacle to be found in the shape of surface re- 

 sistance, except what are as a few grains of dust compared with the obstacles 

 to be found on the common road, or the deep ruts in a wood, which require 

 very large wheels for the timber wain. " At the same time (continued the 

 commissioners), the load itself may be reduced in height, the bottom of the 

 carriage, or truck frame, being, in this case, limited by the axletree of the 

 larger, instead of the periphery of the smaller wheel, and, with this reduction 

 of hei"ht, the wear and tear will be reduced, and the case of the motion 

 increased. Moreover, the force to be overcome being less with the same load, 

 we may, by retaining the power of the engine the same, carry a greater load 

 than at present with the same velocity, or, retaining the same load, carry it 

 at a "reater velocity by increasing the diameter of the driving wheels of the 

 engine; or, if it be not desirable to increase the velocity, the speed of the 

 piston might be reduced, which would be a great practical advantage; or, 

 lastly, preserving the same load and velocity, the form and weight of the 

 engine may be made less, and, probably, the one or other of these arrange- 

 ments would he adopted, acconling to the nature of the traffic on the rail- 

 way. Thus, in passenger and mail trains, it might be desirable to increase 

 the velocity, whereas, in the carriage of hea\-y goods, it would be most eco- 

 nomical to increase the load." '• But (say the commissioners) there is a 

 pohit which must be attended to, and tliat is, that the whole of the advan- 

 ta"es apply only to level lines." Now the Grer.t Western was thus suscep- 

 tible of having a wider gauge, since the line was made nearly level, for, as 

 the commissioners observe, " in ascending the various gradients and inclined 

 planes, the load has to be raised in opposition to gravity, and the power 

 necessary to effect this is frequently equal to, or exceeds, that which is em- 

 ployed to overcome the fric'.ion, and wdl remain the same to whatever ex- 

 tent the friction is reduced. To avail ourselves fully of the reduced friction, 

 those planes which cannot be worked by assistant power require to be re- 

 duced in Ihe'ir slopes, in the same proportion that the wheels are increased, 

 or, otherwise, that assistant power be applied on proporlionably less slopes 

 than according to the present practice" — that is to say, that the power of 

 the engine is employed in overcoming the friction of ihe load, and in raising 

 it up the several ascents, and what is gained by increa.sing the breadth of 

 the railway and making the wheels run outside the frames, is only applicable 

 to the former, the latter remaining the same as before ; " and the advantage 

 of the alteration would be overrated if this circumstance wt-re not taken into 

 consideration." Thus it is that the additional advantage arising from the 

 diminution of friction is so small, when you come to otiier than nearly hori- 

 zontal lines, that the advantage is lost. There is yet another reason for 

 increasing the gauge— viz. that we are enabled to construct the machine 

 without being cramped in space for the moving p:trts, and affording a larger 

 diameter for the boiler ; it was this consideration, probably, which first in- 

 duced practical engineers to pay attention to incre:ising the gauge above 

 4 ft. Si in. If we had to begin railways again, we should certainly make the 

 gauge wider than 4 ft. 8i in. Inlaying out future lines, particularly where the 

 traffic is not great, the point of consideration will be to obtain the greatest 

 advantage at the least expense, and to determine how much the gauge ought 

 to be increased ; and Mr. Vignoles stated, that, after having paid a deal of 

 attention to the subject, he gave it as his opinion, that a gauge of six feet 

 would be amply sufficient to satisfy all reasonable conditions. The Irish 

 Railway Commissioners had observed, " that, at present, the load is seldom 

 equal to Ihe power of the engine, and, this being the case, but little would 

 be gained by a greater breadth of road," with a view only of reducing the 

 resistance, already much inferior to the power by which it is to be ovtrcome, 

 except by allowing an increased s-peed on the line generally, and on the level 

 planes in particular. With a full and overflowing trafiic, there is no doubt 

 it would be advisable to employ the greatest possible breadth of bearing ; 

 but it is useless, or worse than useless, to incur a present expense for a benefit 

 which it is not likely that there will ever be the means of taking advantage 

 of, so that, unless under the circumstances just mentioned — viz. an incessant 

 traliic, Mr. Vignoles thought that a seven-feet gauge was over the mark. 

 Mr. Vignoles stated, that the consideration of curves was connected with 

 that of the gauge, that it was a most important element in the consideration 

 of railways, and would be taken up in another lecture. The rule given for 

 raising the outer rail, on curves, required the gauge to be included as one 

 element in the calculation, as also the height of the cenire of gravity above 

 the rails, which was also contingent on the gauge, as before explained. 



INSTRUMENT FOR CALCULATING VELOCITIES ON 

 RAILWAYS, &c. 



(With an Engraving, Plate IX. J 



The instrument represented in the annexed plate, which I have 

 named a "Veloci meter," is intended to supersede tlie long calculations, 

 frequently necessary, in obtaining velocities in engine trials. 



When the times of passing tlie quarter mile posts only are noted, 

 such an apparatus is hardly called for, since, tlie distances being con- 

 stant, a table may readily be made out which will give the velocitiesr 

 due to the diflerent times ; hut it is a common practice, and perhaps a 

 more satisfactory one, to note the times taken in traversing the several 

 gradients, where the distances as well as tlie times are variable. The 

 lengths of the inclines are generally fractional, and probably no two 

 are the same, and none of the times of travelling over them are equal; 

 consequently each case involves a distinct calculation, and where the 

 trials have been extensive, several days may be occupied in making 

 these reductions. It is, therefore, a desideratum to have some other 

 means of obtaining the velocities, than that aftbrded by the ordinary 

 methods of calculation. 



The instrument devised for this purpose, is another application of 

 that very important geometrical principle — the equality of the ratios 

 of the sides of similar triangles. In the right angled triangle ABC 

 (Fig. 1), let A B be taken to represent any given number of minutes 

 and seconds, and A C the number of miles and chains passed over in 

 that time. Then, if A B be produced until it becomes equivalent to 

 an hour, and from its extremity D, a perpendicular be drawn inter- 

 secting A C produced in E, A E will represent the number of miles 

 that would have been traversed in the hour had the motion been 

 continued, that is, it will indicate the rate per hour at which the dis- 

 tance A C was travelled. Now, if A E be made to revolve round A, 

 and to take any other positions, as A E' or A E," it is clear that the 

 relations will still be the same, and that if any distances A C,' or A C," 

 be described in the time A B, A E' and A E" will indicate the re- 

 spective rates per hour. If, in addition to this, B C be made moveable 

 along A D, or, what is the same thing, if A D be divided into minutes 

 and seconds, and lines be drawn from the divisions parallel to B C, 

 we shall be able to adjust the revolving line, to any distances and times, 

 within the limits that may be allowed by the arrangement. 



It will probably be objected, that if the line A D, representing an 

 hour, is to be divided into minutes and seconds, its length must be so 

 great as to make the instrument too unwieldy for common use. This 

 difficulty is, however, very readily surmounted. 



If A D (Fig. 2), be taken to represent a quarter of an hour, instead 

 of an hour as in the last figure, it follows, that other things being the 

 same, A E will represent one-fourth of the number of miles per hour; 

 that is, if A E had four times the number of divisions, it would in- 

 dicate the rate per hour : if, therefore, A E have two scales, one for 

 adjustment and the other with divisions one-fourth the size for indica- 

 tion, the velocities may be read off as before. Or if it be desirable 

 to make use of one-tenth of an hour, instead of one-fourth, we have 

 only to mike the indicating divisions, one-tenth of the size of the 

 adjusting divisions, and the same result will follow. 



In the application of this principle to practice, the following 

 arrangements are made : — A D is the scale of time, embracing in this 

 case one-tenth of an hour, or six minutes ; each minute includes 15 

 divisions, one of which will, therefore, represent 4 seconds, and as 

 each of these may be readily bisected by the eye, the scale may be 

 considered as divided into periods of two seconds each. A E is the 

 scale of distance, turning on the centre A, the adjusting scale being 

 divided into 4 miles, and each of these subdivided into 80 chains; 

 the same space is divided on the indicating scale into 40 miles, and 

 each of these into eighths, ten miles on the one scale being equivalent 

 to one on the other, in consequence of the time scale extending only 

 to one-tenth of an hour. 



To obtain results by this apparatus, the revolving scale is moved 

 until the division answering to the number of miles and chains passed 



2 K 2 



