18.(Pg. [29]) The air is more dense near the surface of the earth, and decreases in density as you ascend, how is this accounted for, and to what is it compared?
19.(Pg. [29]) What is it which causes the particles of air to recede from each other, and seems to destroy their mutual attraction?
20.(Pg. [29]) Smoke and vapour ascend in the atmosphere, how can you reconcile this with gravitation?
21.(Pg. [30]) How would you illustrate this by the floating of a piece of paper on water?
22.(Pg. [30]) Does smoke rise to a great height in the air, and if not, what prevents its so doing?
23.(Pg. [30]) What limits the height to which vapours rise?
24.(Pg. [30]) Of what does smoke consist?
25.(Pg. [30]) Air balloons are formed of heavy materials, how will you account for their rising in the air?
26.(Pg. [30]) What influence does the air exert, on bodies less dense than itself, on those of equal, and on those of greater density?
27.(Pg. [31]) If the air could be entirely removed, what influence would this have upon the falling of heavy and light bodies?