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 G H: The Balance or Lever I K: the
Screw F; which includes the Wedge: and the Pulley L M. 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 A B join'd by a Chain to its
Fusee C D, 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 E F,
either equal (as here,) or else lesser, or greater, than the hinder G H;
to be drawn by a Weight w in the Scale, either upon an Horizontal, or upon
an Inclined Plain A B, and to get over any Obstacle as C D: 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 O P, and its Winch R, and
String O P L K, its lesser Barrel K L, circular Table A B, Scale with a
Weight w, suspended by a String that comes through the hollow Axis C D,
and oblique Tube G C, 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.
[[Plate VI. ― Sutton Nicholls sculp:]]