17.(Pg. [198]) Why does placing an object near the eye, enable such, to see distinctly? [fig. 6.]
18.(Pg. [199]) A concave lens remedies this defect; how? [fig. 1, plate 22.]
19.(Pg. [199]) What is the remedy, when a person is long-sighted? [fig. 2.]
20.(Pg. [199]) Why does holding an object far from the eye, help such persons? [fig. 3.]
21.(Pg. [200]) How is the eye said to adapt itself to distant, and to near objects?
22.(Pg. [200]) Why are objects rendered indistinct, when placed very near to the eye? [fig. 4, plate 22.]
23.(Pg. [200]) What is the single microscope, [fig. 5], and how does it magnify objects?
24.(Pg. [201]) How may objects be magnified without the aid of a lens?
25.(Pg. [201]) Why can an object, very near to the eye, be distinctly seen, when viewed through a small hole?
26.(Pg. [201]) Describe the double microscope, as represented in [fig. 6, plate 22.]