94 MOTIVE POWER AND DISPOSITION

riages, that the action of gravity can be usedto advantage.

It will, therefore, be of importance, in thesubject of Rail-road conveyance, to ascertainupon what declivities, with a given prepon-derating load, this power is available.

The object of all such inclined planes beingto convey down a certain quantity of goods ina given time, and to do this with the leastexpenditure of power ; in forming a Rail-road, therefore, with a view of using thisspecies of traction, it is not only necessary thatthe descent of the plane be such as to give a pre-ponderance to the loaded carriages over thosewhich are empty, but such a preponderanceas will cause them to descend and drag up theempty carriages with the requisite velocity.If we give to the plane a greater inclinationthan requisite, we expose the rope and car-riages to an unnecessary strain, and, conse-quently, to additional wear and cost; and iflliat inclination be not sufficient, tlie properperformance will not be accomplished. I shalltherefore endeavour to develope the laws whichgovern bodies descending inclined planes, andafterwards give such practicable illustrations asI trust will render the subject a matter of easycalculation to those interested.

The phenomena of falling bodies is now