BOOK II.

THE TELESCOPE.

V.— THE REFRACTION OF LIGHT 55

VI.— THE REFRACTOR 73

VII.— THE REFLECTION OF LIGHT 90

VIII.— THE REFLECTOR 100

IX.— EYEPIECES 109

X.— PRODUCTION OF LENSES AND SPECULA 117

XI.— THE “OPTICK TUBE” 139

XII.— THE MODERN TELESCOPE 152