We find in an exchange an article endeavoring to draw amusement from the writings of Vitruvius, upon the principles of mechanics. One of the extracts made from this ancient author, who lived a short time previous to the birth of Christ, is the following : “ I have briefly explained,” he says, “ the principles of machines of draft, in which, as the powers and nature of the motion are different, so they generate two effects, one direct, the other circular, but it must be confessed that neither rectilinear nor circular motion can without the other be of much assistance in raising weights." Now, so far from seeing anything very amusing in this statement, the more we consider it the more we feel surprise at the comprehensiveness of the proposition. We see in it a generalization, the truth of which is exemplified in every machine. So large a proportion of the motions of the parts of machinery may be included in ths classes rectilinear and circular, that the very few exceptions wherein the curvilinear motions are other than these, are scarcely worth consideration; and wherever they are employed it is always at a sacrifice of economy in power, the former motions being the least expensive of movements. Where, as in the case of the crank and pitman, a rectilinear motion and circular motion are coupled, there may be a loss in the application of the power to useful work, always consequent upon the increase of the number of moving parts in a machine; but when a crank drives a pitman, or winds up a rope on an axle, the losses suffered in these arrangements of working parts, are consequent upon practical difficulties. In theory there should be no loss. We know that these losses are referable to friction, inertia of parts, rigidity, etc. , and therefore in theoretical formula We may justly pride ourselves on modern progress in science ; but the old philosophers undoubtedly saw and comprehended more than is sometimes credited to them.
This article was originally published with the title "Circular Motion and Rectilinear Motion" in Scientific American 21, 17, 265 (October 1869)