FIRST DIALOGUE

greater clarity we will imagine to be a small rope: there is no doubt that by pressing the two cylinders strongly one against the

A technical diagram illustrates mechanical friction. Two vertical cylinders are shown, labeled C D (left) and A B (right). A thick, multi-strand rope labeled E F passes vertically between the two cylinders. A second, identical rope is wrapped in a spiral around cylinder A B. The spiral path is labeled with letters A, F, L, O, T, and ends at a point labeled R, where the rope extends outward. The ends of the ropes (E, F, R) are shown as frayed bundles of fibers.

other, the rope FE pulled from the extremity F will resist a not insignificant violence before sliding between the two compressing solids: but if we remove one of them, the rope, although it continues to touch the other, will not be retained by such touching so that it does not slide freely. But if, while holding it albeit weakly attached towards the top of the cylinder A, we wrap it around that in the manner of a spiral A F L O T R, and from the end R we pull it: it is manifest that it will begin to tighten the cylinder, and if the coils and turns are many, the rope will compress itself ever more onto the cylinder in the act of being powerfully pulled: and the touching becoming longer with the multiplication of the coils, and in consequence less superable, it will become ever more difficult for the rope to slide and consent to the pulling force. Now who does not see that such is the resistance of the filaments, which with thousands and thousands of similar wrappings compose the thick rope? Indeed, the tightening of similar twistings connects so tenaciously that from not many rushes, nor even very long ones, so that there are few coils with which they intertwine among themselves, are composed very sturdy ropes, which I think they call suste springs/cords.

Sagr. Through your discourse, the wonder in my mind ceases regarding two effects, of which the reasons were not well understood by me. One was seeing how two, or at most three turns of the rope around the spindle of the winch could not only retain it, so that pulled by the immense force of the weight it supports, it would not yield by sliding, but that furthermore, by turning the winch, the same spindle, by the sole touching of the rope that tightens it, could with the succeeding wrappings