56

HISTORY AND PROGRESS

least tremor of the carriage; but immediatelythat you come upon the other, a continuance ofjolts and shakes is felt, as the carriage-wheelssuccessively pass over each joint. The injurycaused to the carriages, though not immediatelyfelt, yet, by frequent repetition, must eventuallytend to shake them in pieces; the wear of thewheels of the carriages also, by the blows, willbe considerable.

Nothing, however, is of greater importance,in estimating the benefits obtained by this modeof fixing the rails, than the diminution of theresistance opposed to the wheels of the carriages.Many practical examples could be adducedwhere the difference has been found to be verygreat indeed; the projections acting as succes-sive obstacles to retard the progressive motionof the wheels, and which were to be surmountedat every joining.

Various modifications of this mode of fixingthe rails have been attempted ; to describe thewhole of them would be impossible.

C and D, Fig. VII. Plate II. Shew two which are worthnotice. In the first, the ends of the rails are square, similarto the old rails; at each end a semicircular indentation ismade, equal in diameter to the pin-hole in the chair; whenthe ends of the two rails are laid together, a circular holeis formed, through which the pin is driven, passing throughthe chair on each side of the rail; the pin has no effect infastening them together in the direction of their length, but