Lectures de Potentia Restitutiva, or of Spring

By measuring the distances of all those marks and comparing them together, you shall find that they will all be equal to one another. For example, if one drachm original: "drachm"; a unit of weight equal to 1/8 of an ounce moves the wheel ten degrees, two drachms will move it twenty, three will move it thirty, four will move it forty, five will move it fifty, and so on.

Alternatively, take a wire string twenty, thirty, or forty feet long and fasten the upper part of it to a nail. To the other end, fasten a scale to hold weights. Then, with a pair of compasses, measure the distance from the bottom of the scale to the ground or floor underneath and record that distance. Next, put weights into the scale in the same manner as in the previous trials, measure the various stretchings of the string, and record them. When you compare the various stretchings of the string, you will find that they will always maintain the same proportions to one another as the weights that caused them.

The same result will be found if a trial is made with a piece of dry wood that is flexible enough to bend and return to its shape. If one end of the wood is fixed in a horizontal position and weights are hung from the other end to make it bend downwards, the same proportions will apply.

I published the method for testing this same principle on a body of air—whether regarding its rarefaction the reduction of a medium's density; the opposite of compression or its compression—about fourteen years ago in my book Micrographia. Therefore, I do not need to add any further description of it here.

Each of these methods will be more clearly understood by the explanations of the attached figures.

The first figure represents the coil or helix a spiral shape of wire by the letters A B. C is the end by which it is suspended, and D is the other end, from which a small scale, E, is hung. By placing weights—labeled F, G, H, I, K, L, M, N—into the scale one by one, with the weights being in proportion to one another as 1, 2, 3, 4, 5, 6, 7, and 8, the spring will be stretched equally to the points o, p, q, r, s, t, u, w.