27.(Pg. [174]) What substances form the most perfect mirrors, and for what reason?
28.(Pg. [174]) What are the three kinds of mirrors usually employed for optical purposes?
29.(Pg. [174]) How are the rays of light affected by them?
30.(Pg. [175]) What is the form of a convex mirror, and how do parallel rays fall upon it, as represented in [fig. 1, plate 18]?
31.(Pg. [175]) What is represented by the dotted line in the same figure?
32.(Pg. [175]) Explain by the figure, how the parallel rays will be reflected.
33.(Pg. [175]) At what distance behind such a mirror, would an image, produced by parallel rays, be formed?
34.(Pg. [175]) What is that point denominated?
35.(Pg. [176]) What is meant by a focus?
36.(Pg. [176]) Why is the point behind the mirror, called the imaginary focus?