702 



RAILWAYS. 



iu.ojited, in passing a curve, the win-el that moves 

 on the outside or longest rail must be slided over 

 whatever distance it exceeds the length of the 

 other rail, in case both wheels roll on rims of the 

 same diameter. This is an obstruction presented 

 by almost every railroad, since it is rarely practi- 

 cable to make such a road straight. The curva- 

 tures of some roads are of a radius of only 300, 

 and even of 250 feet. The consequence was that 

 the carriages heretofore in use were obstructed, noi 

 only by the rubbing of the surfaces of the wheels 

 upon the rails, already mentioned, but also by the 

 friction of the flange of the wheel against the side 

 of the rail. This difficulty has, however, been in a 

 great measure remedied by an improvement made 

 in the form of the rim of the wheel. The part on 

 which this rim ordinarily rolls on the rail, is made 

 cylindrical, this being the form of bearing evidently 

 the least injurious to the road, as the weight resting 

 perpendicularly upon the rails has no tendency to 

 displace them or their supports. But between this 

 ordinary bearing and the flange, a distance of about 

 one inch in a wheel of thirty inches diameter, the 

 rim was made conical, rising towards the flange one 

 sixth of an inch, and thus gradually increasing in 

 diameter. Wherever the road bends, the wheel, 

 rolling on the exterior, and, in such case longer 

 track, will, in consequence of the tendency of the 

 carriage to move in a right line, be carried up a 

 little on the rail, so as to bear upon the conical 

 part of the rim, which gives a bearing circumfer- 

 ence of the wheel on that side, greater than that of 

 the wheel at the opposite end of the same axle. 

 The tendency, accordingly, is to keep the car in 

 the centre of the tracks, by producing a curvilinear 

 motion in the wagon, exactly corresponding to the 

 curve of the road. In the report made by Mr 

 Knight (of the United States of America), in 

 1830, he says that a car, with wheels such as 

 those already described, was run upon a part 

 of the Baltimore and Ohio railroad, where 

 the greatest curvatures were of a radius of 400 

 feet, at the rate of fifteen miles per hour. 

 In his report of October 1, 1831, Mr Knight says 

 that the additional friction on such a curve, above 

 that on a straight road, is 1 in 1418, equal to 3.72 

 feet in a mile, with Winans's car, and 1 in 356, 

 equal to 14.83 feet in a mile, with another car. I if 

 the diameter of the wheel is increased, that of the 

 conical part of the rim should be increased also, 

 making the rise of the conical part between the 

 flange and the cylindrical part (as Mr Knight estimates 

 in his report of February 1, 1830), one fifth of an 

 inch in a wheel of three feet diameter, and one 

 fourth of an inch in a wheel of four feet diameter. 

 In his report of October 1, 1831, he says he had 

 changed the ratio of the conical part of the rim, on 

 wheels of the same size, from that of one to six, to 

 that of one to five, and had increased the length of 

 the conical part to 1^ inch : and that he thinks 

 the form of the rim was thereby improved. In the 

 same report, Mr Knight describes a method of turn- 

 ing a very short curve of a quadrant of a circle on 

 a radius of sixty feet, by making a plate with a 

 groove for the flange of the wheel on the longer 

 track to run in ; thus, in this case, making the dif- 

 ference of the rolling circumference of the wheels 

 correspond to that of the two tracks. This plan 

 was adopted for the purpose of turning corners of 

 streets in towns, and, from experiments that have 

 been made, promises to be successful. 



Inclined Planes. Where the inclination of the 

 road is greater than that for which the ordinary 

 power is calculated, the ascent must be effected by 

 means of an additional power, the amount of which 



can be readily computed, since, in those pails, no 

 additional friction of the cars or wheels is to be pro- 

 vided for, and only the additional resistance arising 

 from gravity is to be overcome. If, for instance, 

 the additional inclination is one in ninety-six.or fifty- 

 five feet in a mile, the additional power must be u. 

 the weight as one to ninety-six, or as fifty-five to 

 the number of feet in a mile, namely, 5280. In de- 

 scending planes, so much inclined that the gravity 

 would move the carriages too rapidly for safety, tin- 

 velocity is checked by means of a break, which 

 consists of a piece of wood of the same curvature as 

 the rim of a set of the wheels, upon which the break 

 is pressed by means of a lever, so adjusted as to be 

 within reach of the conductor, in his position on the 

 carriage. 



Power. Gravity, horse power, and steam power, 

 have been used on rail-roads. Where the road is 

 sufficiently and uniformly descending in one direc- 

 tion, gravity may be relied upon as a motive power 

 in that direction ; but on rail-roads generally, some 

 other power must be resorted to in each direction. 

 At the time of the construction of the Liverpool 

 and Manchester rail-way, much discussion took 

 place, as to the expediency of using stationary or 

 locomotive steam-engines. The result of the deli- 

 berations was, that if locomotives could be con- 

 structed within certain conditions as to weight and 

 speed, they would be preferable. The directors 

 accordingly offered a premium for the construction 

 of such a locomotive, as should perform according 

 to the conditions prescribed. At the celebrated 

 trial on that road in October, 1829, of which Mi- 

 Wood gives a particular account in the edition of 

 1831 of his work on rail-roads, the locomotive, cal- 

 led the Rocket, constructed upon the plan of Mr 

 Robert Stevenson, was found to come within the 

 proposed conditions, and accordingly the decision, 

 in respect to that road, was in favour of locomotives. 

 The opinion in favour of this kind of power on roads 

 of which the inclination does not exceed about 

 thirty feet in a mile, has become pretty fully estab- 

 lished. Stationary power can be used to advantage 

 only on lines of very great transportation, as the 

 expense is necessarily very great, and almost the 

 same, whether the transportation be greater or less. 

 Another objection to the use of stationary power is, 

 that its interruption, in any part, breaks up the line 

 for the time, which is not necessarily the case with 

 a locomotive. The alternative, accordingly, is 

 between the use of locomotive steam engines or 

 horses, and the choice must be determined by the 

 particular circumstances of the line of transporta- 

 tion. The advantages of this species of road are 

 illustrated by the action of a horse upon it, compared 

 with his performance upon the best turnpike, being, 

 as Mr Wood assumes in one of his estimates, in the 

 proportion of 7.5 to 1 ; thus enabling us to dis- 

 pense with thirteen out of fifteen horses required 

 for transportation on the best common roads. The 

 horse's power of draught is much the greatest at a 

 low rate of speed, since the more rapid the velocity, 

 the greater proportion of his muscular exertion is 

 required to transport his own weight. But it is 

 ascertained, on the Baltimore and Ohio rail-road, 

 that a speed of ten miles an hour may be kept up 

 by horses travelling stages of six miles each, which 

 would perform the whole distance between Balti- 

 more and the Ohio river in thirty-six hours. The 

 whole expense of transportation by horse power, 

 including cars, drivers, and every expense except 

 repairs of the road, on the same rail-road, from 

 January to September, 1831, amounted to about 

 one third of the gross tolls received ; and this ex- 

 pense, it was calculated, might be very materially 



