General Theater of Machines

arts. However, out of habit, this distinction is rarely observed, and someone who called a blacksmith's tongs or a tailor's scissors "machines" would be considered quite ridiculous by them. For a Mechanic original: "Mechanico"; a practitioner of the mechanical arts, it is enough if he knows where to place each thing.

In every machine, several elements occur, and it is first necessary to know what they are:

I. The Point of Rest, or center of motion original: "Centrum motus".
II. The Load, or object, or the capacity original: "Pondus".
III. The Force original: "Potentia".
IV. The Distance or the Leverage original: "Distantia potentiæ vel ponderis".
V. The Space or the Time original: "Spatium".

I. The Point of Rest is, in mechanics, a point or place where a load or machine rests and upon which it is moved; from this point (or its line), the distance of both the load and the force is to be calculated. Examples include the sharp edge of the support C of the lever in Plate I, Figures I and II, as well as at D on the levers in Figures V, VI, VII, XI, and XII. In the case of wheels and pulleys, these are the pivots or axles; in scissors or tongs, they are the pins or rivets, and so forth.

(1.) This Point of Rest is distinguished from the Center of Gravity original: "Centro gravitatis" in that the latter is a point within every body by which it can be divided into two equally heavy parts, much like the center of a sphere. How this center is to be found in every regular and irregular body will be taught in the future section on Statics The branch of mechanics concerned with bodies at rest and forces in equilibrium.

(2.) The Point of Rest is also distinguished from the Center of Magnitude original: "Centro magnitudinis", for the latter only divides a surface into two equal parts and does not take their weight into account.

(3.) The Line of Rest is a straight line which always passes through the point of rest and runs parallel with the Line of Motion original: "Linea Directionis", and from which the distance of the force or the load is calculated. For example: in Plate III, Figure I, the weight or sphere A weighs 4 pounds, and therefore requires a counterweight of 4 pounds in a horizontal position A E. However, if such a sphere stands on the line f G, the distance is no longer measured from the center of the sphere to the axle E, but rather along the line R C—namely, only 2 parts of E A. Thus, if the sphere stands at H, the distance-line is I H. Therefore, R C and I H are not taken from the center or Point of Rest E, but from the Line of Rest R E R, yet in such a way that the distance-line makes an equal angle with the Line of Rest. Similarly, in Figure IV, the Line of Rest is R R, and the distance-line of weight B is H b, while for weight A it is G I.

(4.) This is called the Line of Rest because both the load and the force, when they stand in this line, lose their power, or can be moved out of it with very little effort; as can be seen in Figure XI, Plate II, at weight e, which can be moved quite easily with the tiny weight b. However, because the Line of Rest must constantly align itself with the Line of Direction original: "Linea directionis", it is also necessary to know what this actually is.

The Direction Line, or the Line of Motion, is a straight line along which the force and load either move themselves or are moved, if they find no hindrance. This is seen in Figure VII, Plate VII, where the weights A B C naturally fall perpendicularly or downward toward K because of their weight, if they were not hindered; because they are fixed to the wheel, they must run at the same distance around the center or axle. Therefore, here the Direction Line is the same as the perpendicular Line of Rest H I; but in Figure VIII, the Direction Line is A B, because the arm B C is pulled toward A by a cord, and thus deviates entirely from the perpendicular line D E; therefore also