velocity in the motion; and each experiment was repeated until we were perfectly satisfied of the accuracy of the result. The degree of force indicated by the dynamometer, was, therefore, that which was required to keep the waggon in motion, or to keep it in a state of uniform velocity, that velocity being first produced by other means. Experiments made at Killingworth colliery, with the dynamometer, to ascertain the friction or resistance of carriages moved along railroads. The rails were of cast iron.-Edge-rails of Messrs. Losh and Stephenson, Fig. 2, Plate II. Flat bearing surface, two inches and a half broad; three feet, nine inches and a half long; the plane, a piece of road selected for the purpose, was quite straight, and with a uniform inclination of .0738 inches in a yard, or one yard in 488. The carriages were the same as used upon the road for the conveyance of coals, and similar in shape to that shewn in Figs. 1, 2, Plate VII. The wheels were fixed upon the axles, and turned with them; their diameter was thirty-four inches, with a projecting ledge of three-fourths of an inch, to keep them on the road. The body of the carriage rested by a chair of brass or iron upon the axles of the wheels, as explained in the detail of the experiments; the axles being of wrought-iron, two inches and three quarters in diameter, at the bearing. EXPERIMENT I. Number of experiments. Description of carriages. Resistance up Resistance down the plane. Mean resistance, Friction in parts Loaded carriage, weighing 23 cwt., and 74 91 48 39 89 63 186 112 277 *After the above experiments were performed, there appeared such a variation in the result, between the carriages having different kinds of wheels, and bearings; the following were made to ascertain how much the resistance was affected by each. A very material difference in the result, will be found in the construction of the carriages, used in these experiments. The carriage No. 1, was of the most modern construction, and the resistance upon a level plane amounted to no more than thirty-nine pounds, or th part of the weight. The carriage No. 2, required sixty-three pounds, orth part of the weight, almost two thirds more; but as the bearings and wheels were different, it was desirable to find to which the variation was attributable. On comparing No. 8, and No. 10, together, which had the same kind of bearings, but different wheels, it will be seen that in the four empty carriages, there is a difference in the resistance of twenty-one pounds, which must arise from the wheels alone. The whole weight of those carriages was ninety-three hundred weight; therefore, the additional resistance occasioned by wheels, partly worn or indented into a groove around the rim, amounts to nearly the 500th part of the weight. Again, on comparing No. 7, and No. 8, we find the difference nearly the same, amounting to the 550th part of the weight. This proves the great superiority of case-hardened wheels over the common ones; not only in economy, but also in lessening the resistance. In examining the experiments, there is also another variation in the result, owing to the different kinds of bearings employed. Comparing the resistance of No. 8, with No. 7, there appears a difference of four pounds, which is equal to one pound in each bearings of cast iron and of brass. are broader than those of the brass, haps, account for the difference; otherwise the brass would most likely have been found to present the least friction, but it at the same time proves the necessity of carriage between The iron bearings and this will, per making the bearings of a certain area, compared with the pressure upon them, and shews that the brass is considerably below that area; inasmuch, as we find that the increased breadth of the cast iron, more than compensates for its inferiority to brass, in diminishing the friction. We had also an opportunity of subjecting to the test of experiment, another kind of bearing, which for a long period after the introduction of railways was universally used, and we believe is still used in some places. This is a malleable iron bearing, formed by the hammer of the blacksmith, one inch and a quarter broad. This was the bearing used in No. 11, which, on being compared with Nos. 7, and 8, a difference will be found amounting to nineteen pounds, between that kind of bearing and the cast iron, and fifteen pounds between it and the brass; which is equal to the difference between the common and the case-hardened wheels, and amounting to nearly the 550th part of the weight. This is not the only evil produced by the use of this kind of bearing; it also operates very powerfully in cutting the axles. On being shewn two axles, it is readily distinguishable to which kind of bearing each has been subjected; the axle with the narrow bearing is cut and furrowed, while the other is smooth and even; and it need not be stated the effect which such a cause would produce in the expence, by the destruction of axles. The reduction of friction, by the introduction of broad bearings and case-hardened wheels is very considerable, and when properly estimated, are of great moment in the economy of railroad conveyance. The two together, amount to the 275th part of the weight of the carriage, or equal to forty-three per cent. of the whole amount of friction. Third.-Hetton Experiments. The following are some experiments, which I made upon the Hetton Colliery railroad, in December 1824, which, as determining the friction by other methods, will be interesting, as a comparison with the preceding. Length of plane, 1164 feet, perfectly straight, with an uniform and regular descent of one yard in 104,24, or eleven feet, two inches, in the whole distance; edgerail, of Losh and Stephenson's patent, two inches and a half broad at top. The carriages were allowed to descend freely by their gravitating force, and the space they passed over, ascertained by a stop-watch. EXPERIMENT II. Four loaded carriages, each weighing 9408 lbs., with case hardened wheels, two feet eleven inches in diameter, malleable iron axles, three inches diameter, bearing cast-iron, four inches broad. Space described, 1164 feet; time, 120 seconds. Supposing w = 8906 and w (as per experiment) 2095 lbs.; we SG Seven loaded carriages, similar to the above, described precisely the same space in the same time, making their friction the same as above - viz. 39 35 lbs. During the time of performing these two experiments, it was a dead calm, not the least wind; and the rails were dry, and in that state which would present almost |