An Explication of the Fifth Plate.

Figure 1. Is a Compound Engine in which all the several Mechanical Powers are combin'd: as the Wheel and Axle GH: The Balance or Lever IK: the Screw F; which includes the Wedge: and the Pulley LM. The entire Force of this Engine is to be computed by compounding the separate Forces together.

Fig.2. Is a Windmill; whose Force is here represented, by its raising a Weight on a Barrel. The Wind is supposed to blow parallel to the Axis, from E towards D; its several Sails have their Plains nearly 45 Degrees oblique to the Plain through the middle of those Sails: Two of them inclining, and two reclining. By this Means the Wind falling at about 45 Degrees obliquity on the Plain of each Sail; the Breadth of each Sail is a Diagonal of a square, one of whose Sides is parallel to the Direction of the circular Motion, and has its full Force; and the other is perpendicular thereto, and so has no Effect as to that circular Motion at all. And as much as the Side of a Square is lesser than the Diagonal, so much of the whole Quantity of the Wind is lost on every single Sail. But then each Pair along the same Line, by the different Situation of those Sails, agreeing in the same Motion, the whole united Quantity is more than the single Quantity upon one equal Sail directly expos'd to the same Wind, as much as two Sides of a Square are greater than the Diagonal. But this without the Consideration of the weakning of the Force of the Wind by the Obliquity of Incidence; which alters the former Proportion: for this also diminishing the Force in the same Proportion with the former Diminution of the Quantity of the Wind, the whole Diminution will ever be as the Squares of that Quantity; or as the Squares of the Sines of the Angles of Incidence: wherefore in this Case of Four oblique Sails of 45 Degrees will be equivalent to Two direct ones.

Fig.3. Is the elastical spiral Spring of a Watch, out of its Box, and unwinding it self more weakly, as it is less restrained.

Fig.4. Is the same Spring in its Barrel AB join'd by a Chain to its Fusee CD, or spiral Line about a Cone, which Cone has the Semidiameter or Distance from its Axis in the very same Proportion, greater as the Spring is weaker, and lesser as the Spring is stronger: that so the absolute Force on the Wheels of the Watch may be ever the same, for the exact Equality of their Motion in all Cases.

Fig.5. Is an Imitation of a Waggon or Coach, with its fore Wheels EF, either equal (as here,) or else lesser, or greater, than the hinder GH; to be drawn by a Weight w in the Scale, either upon an Horizontal, or upon an Inclined Plain AB, and to get over any Obstacle as CD: The Quadrant M, and Bullet N, are to shew the Quantity of the Elevation of that Plain, for the Tryal of Experiments relating to all such Sort of Vehicles.

Fig.6. Is a strong Machine, with a Wheel OP, and its Winch R, and String OPLK, its lesser Barrel KL, circular Table AB, Scale with a Weight w, suspended by a String that comes through the hollow Axis CD, and oblique Tube GC, in which Mercury or a Bullet is included; its Screw H; its Balls I and B, and their Strings; To shew that Motion once begun always continues, till some other Cause stops it: That absolute and respective Motion are entirely different: And to shew withal the Endeavour of Bodies that move circularly to recede from the Center of their Motion, on inclined, as well as horizontal Plains, and that in the same Circle in a duplicate Proportion to their Velocity.