9.(Pg. [81]) Does this apply to any power excepting gravitation?
10.(Pg. [81]) How is it that a secondary planet revolves round its primary, and is not drawn off by the sun?
11.(Pg. [82]) What is said respecting the revolution of the moon, and of the earth, round a common centre of gravity?
12.(Pg. [82]) By what law in mechanics is this explained?
13.(Pg. [82]) What motions then has the earth, and are these remarks confined to it alone?
14.(Pg. [82]) What effect have the planets upon the sun, and what is said of the common centre of gravity of the system?
15.(Pg. [83]) What other motion has the sun, and how is it proved?
16.(Pg. [83]) How may you observe the motion of a planet, by means of a fixed star?
17.(Pg. [83]) What is represented by [fig. 1. plate 7]?
18.(Pg. [83]) Why are the orbits represented as circular?