ON RAISING- AND REMOVING WEIGHTS. .011

Another, the most natural and obvious method, if they are portable, is tocarry them. There is, however, some scope for theory even in this commonoperation, and we have seen that calculations have been made in order to de-termine the most advantageous burden for a porter to carry, but the experi-ence of a few trials would in general be a better guide. Some carry weightson their heads, others on their shoulders, others low down on their hacks: andaccording'to the situation of the burden, they bend forwards or backwards, sothat the common centre of gravity of the weight and the body comes immedi-ately or very nearly over some part of the ground between their feet. 1 hedifficulty of carrying a weight at the extremity of a long rod is easily under-stood from the properties of the lever, and the same principles will enable usto determine the distribution of a load between two porters, in whatever waythey may carry it. Supposing the weight to be placed on a porter's horse, orhand barrow, and at equal distances from both extremities, each of the menwill support an equal portion of it; but if it be nearer to the one thanto the other, the load will he distributed in the same proportion as the polesare divided by the centre of the burden. For instance, it the. weight were300 pounds, and it were one foot distant from the one, and two from theother, the first would have to carry ‘200 pounds, and the second 100. It theporters ascend a hill, or a flight of steps, the distribution of the load will re-gain the same, provided that the centre of the weight lie in the plane of thePoles. But if the weight consists of a large body placed on that plane,the centre of gravity being above it, the effect of an inclination tothe horizon may materially change the distribution of the load, sincetile pressure will always he determined by the distance of the ends of the polesti'om the line passing perpendicularly through the centre of gravity; so tlift,if the elevation were sufficient, the whole burden might rest on the lowerPorter. And in the same manner, if the weight were suspended below theP°K the inclination would cause a greater proportion of the load to be homeV the upper porter. The force is, however, only thus distributed as long astlle arms of the porters continue parallel to each other; but the inequality' v °uld naturally be lessened by a change of the directions in which they wouldact ; it would only be necessary that those directions should meet in some part°* the vertical line passing through the centre of gravity; the magnitudeea -ch force would then be determined by the length of the side of a triangleG ° lres ponding to its direction, and the load might be either equally or un-