288 MOTIVE POWER EMPLOYED

of the piston, travel with the same load at 8miles as at 6 miles an hour; the only powerwanted being an additional quantity of steam,in the proportion of 39:34 above what wasrequired for a rate of 6 miles an hour.

In the application of the loco-motive engineto convey goods upon Rail-roads, the effect,will always be a maximum when the load isthe greatest that the adhesion of the wheelswill permit. The latter will, therefore, bethe utmost limit of their application, and willbe the rule for the inclination of road onwhich they can be made to travel: still theyshould be kept considerably within this limit,or that to which their adhesion will enablethem to effect their own progressive motion,as their utility will depend upon the dragginga load after them; and when this is small,compared with their own weight, then theireffective performance will be reduced below

a profitable standard, and other means should

then be resorted to.

It will scarcely be necessary to give a tableon the weight of goods which a loco-motiveengine can take along a Rail-road with dif-ferent inclinations, as, when occasional ine-qualities occur, the nature of their power willenable them to exert considerably areata*