3.(Pg. [157]) What is meant by a dark body, and what by an opaque body?
4.(Pg. [157]) What are transparent bodies?
5.(Pg. [157]) What is a medium?
6.(Pg. [158]) How is light projected from luminous bodies, and how, from every point of such bodies, ([fig. 1, plate 15]?)
7.(Pg. [158]) Why do not the rays of light from different points, stop each other's progress?
8.(Pg. [158]) What is a ray, and what a pencil of rays? [fig. 2, plate 15.]
9.(Pg. [158]) Do we know whether light is a substance, similar to bodies in general?
10.(Pg. [158]) When a ray of light falls upon an opaque body, what is the result?
11.(Pg. [159]) In what does shadow consist?
12.(Pg. [159]) Why are they, in general, but partially dark?