same_o point_n of_o a_o object_n it_o be_v common_o object_v that_o if_o it_o be_v so_o every_o object_n will_v seem_v in_o two_o place_n at_o once_o vide_fw-la gassendi_n epist._n 4._o de_fw-la magnit_fw-la solis_fw-la humilis_fw-la &_o sublimis_fw-la &_o taqueti_n opt._n lib._n 1._o prop._n 2._o thus_o in_o tab._n 41._o fig._n 3._o 3._o if_o the_o eye_n a_o b_o look_v at_o the_o object_n c_o and_o both_o see_v it_o at_o a_o time_n a_o will_v see_v it_o on_o the_o opposite_a wall_n suppose_v at_o e_o and_o b_o at_z d._n i_o be_o so_o far_o from_o think_v this_o a_o objection_n that_o i_o assert_v first_o that_o we_o do_v see_v all_o object_n in_o two_o place_n and_o that_o this_o be_v not_o take_v notice_n of_o by_o we_o upon_o these_o account_n first_o the_o common_a object_n of_o our_o sight_n be_v large_a and_o the_o axe_n of_o our_o eye_n direct_v to_o but_o one_o physical_a point_n thereof_o at_o a_o time_n and_o then_o we_o can_v be_v expect_v to_o see_v such_o in_o two_o place_n at_o once_o for_o when_o i_o read_v on_o a_o flat_a broad_a book_n where_o be_v the_o opposite_a wall_n for_o a_o single_a small_a letter_n to_o be_v see_v on_o at_o two_o place_n the_o letter_n themselves_o be_v fix_v to_o the_o surface_n that_o determine_v the_o sight_n what_o i_o instance_n in_o letter_n on_o a_o book_n may_v be_v accommodate_v to_o most_o other_o object_n second_o there_o be_v few_o object_n dispose_v fit_o for_o show_v we_o that_o we_o see_v they_o in_o two_o place_n for_o either_o their_o bulk_n hinder_v the_o experiment_n from_o appear_v so_o plain_o or_o their_o distance_n from_o each_o other_o or_o from_o the_o eye_n three_o the_o wall_n de_fw-fr and_o the_o part_n thereof_o be_v see_v so_o confuse_o by_o the_o eye_n a_o b_o when_o fix_v on_o c_o that_o we_o can_v so_o clear_o observe_v this_o experiment_n and_o this_o happen_v to_o all_o object_n more_o remote_a or_o nigh_a to_o we_o than_o c_o when_o the_o eye_n be_v fix_v on_o c_o still_a suppose_v that_o itself_o be_v but_o in_o a_o moderate_a distance_n from_o we_o that_o be_v in_o such_o a_o distance_n from_o we_o as_o may_v bear_v some_o considerable_a proportion_n to_o the_o distance_n of_o the_o two_o eye_n from_o each_o other_o four_o the_o chief_a reason_n why_o we_o do_v not_o perceive_v so_o plain_o the_o object_n c_o to_o cover_z both_z d_o and_o e_z be_v because_o though_o d_o be_v cover_v by_o c_o from_o the_o eye_n b_o yet_o it_o be_v not_o cover_v from_o the_o eye_n a_o and_o therefore_o we_o think_v it_o not_o cover_v at_o all_o also_o though_o e_z be_v cover_v by_o c_o from_o the_o eye_n a_o yet_o it_o be_v not_o cover_v from_o the_o eye_n b_o and_o consequent_o because_o we_o see_v e_o though_o but_o with_o one_o eye_n b_o we_o imagine_v it_o not_o cover_v at_o all_o so_o that_o both_o the_o point_n d_o and_o e_o being_n open_v to_o both_o the_o eye_n a_o and_o b_o viz._n the_o point_n d_o to_o the_o eye_n a_o and_o the_o point_n e_o to_o the_o eye_n b_o we_o think_v neither_o of_o they_o cover_v whereas_o real_o they_o be_v both_o obscure_v each_o to_o its_o proper_a eye_n as_o will_v be_v evident_a by_o wink_v and_o from_o hence_o be_v manifest_v the_o falsity_n of_o taquet_n assertion_n in_o the_o forecited_a place_n viz._n that_o open_v both_o eye_n a_o and_o b_o fig._n 3._o and_o look_v at_o c_o it_o shall_v appear_v only_o to_o cover_v e_o he_o imagine_v that_o most_o man_n see_v general_o with_o their_o left_a eye_n whereas_o i_o say_v it_o shall_v appear_v to_o obscure_v neither_o e_z nor_o d_o though_o to_o each_o eye_n respective_o it_o cover_v each_o five_o whereas_o the_o bulk_n of_o object_n as_o i_o have_v note_v do_v hinder_v the_o experiment_n from_o be_v so_o sensible_o evident_a if_o by_o any_o experiment_n i_o can_v show_v how_o a_o large_a object_n may_v be_v double_v i_o think_v it_o will_v be_v sufficient_o plain_a therefore_o in_o tab._n 41._o fig._n 4._o 2._o let_v a_o b_o be_v the_o two_o eye_n before_o which_o at_o a_o convenient_a distance_n place_n the_o two_o candle_n c_o d_o then_o take_v a_o large_a piece_n of_o paper_n e_o f_o g_o h_n k_n in_o who_o middle_a at_o k_o there_o be_v a_o small_a hole_n this_o paper_n so_o place_n between_o the_o eye_n and_o candle_n that_o the_o eye_n a_o may_v through_o the_o hole_n k_o see_v the_o candle_n d_o and_o at_o the_o same_o time_n the_o eye_n b_o may_v see_v through_o the_o hole_n k_o the_o candle_n c_o the_o due_a distance_n of_o the_o paper_n that_o be_v requisite_a for_o this_o will_v be_v find_v by_o trial_n and_o wink_v alternate_o with_o the_o eye_n when_o all_o thing_n be_v in_o this_o posture_n open_v both_o eye_n a_o and_o b_o and_o direct_v they_o to_o look_v at_o either_o of_o the_o candle_n i_o say_v the_o hole_n k_o shall_v seem_v double_a and_o what_o be_v prove_v of_o the_o point_n k_o be_v true_a of_o all_o other_o point_n in_o the_o paper_n so_o the_o whole_a paper_n appear_v double_a but_o no_o point_n thereof_o be_v so_o evident_o double_v as_o the_o point_n k_o because_o they_o want_v the_o advantage_n of_o light_n behind_o they_o to_o render_v the_o experiment_n more_o sensible_a and_o upon_o this_o occasion_n i_o can_v but_o hint_n to_o all_o person_n that_o be_v desirous_a to_o make_v experiment_n about_o vision_n that_o they_o always_o employ_v the_o most_o luminous_a and_o vigorous_a object_n they_o can_v possible_o for_o many_o experiment_n will_v be_v evident_a by_o they_o that_o will_v not_o sensible_o succeed_v with_o other_o but_o i_o assert_v second_o that_o unless_o we_o see_v with_o both_o eye_n the_o two_o first_o mention_v experiment_n will_v not_o succeed_v and_o they_o may_v be_v reckon_v among_o the_o great_a argument_n that_o can_v be_v produce_v for_o it_o for_o suppose_v in_o fig._n 1._o a_o and_o b_o to_o look_v steadfast_o on_o c_o i_o say_v they_o see_v c_o in_o two_o place_n at_o once_o for_o they_o see_v it_o both_o on_o the_o right_a hand_n and_o left_a hand_n of_o d._n for_o it_o be_v the_o same_o thing_n to_o see_v c_o between_o two_o d_n as_o to_o see_v it_o at_o two_o place_n at_o once_o and_o this_o i_o will_v declare_v more_o full_o tab._n 41._o fig._n 5._o 5._o suppose_v the_o two_o eye_n a_o and_o b_o fix_v on_o the_o object_n c_o i_o say_v c_o appear_v on_o the_o opposite_a wall_n x_o z_o in_fw-la two_o place_n viz._n at_o e_o and_o f_o though_o neither_o e_z nor_o f_o be_v obscure_v thereby_o for_o the_o forego_n reason_n for_o let_v we_o suppose_v the_o object_n d_o of_o the_o first_o figure_n to_o be_v place_v due_o on_o this_o wall_n shut_v a_o the_o object_n c_o shall_v appear_v to_o b_o on_o the_o left_a hand_n of_o d_o by_o the_o angle_n d_o b_o e_o then_o shut_v b_o the_o object_n c_o shall_v appear_v to_o a_o on_o the_o right_a hand_n of_o d_o by_o the_o angle_n daf_n wherefore_o to_o both_o open_a at_o a_o time_n and_o look_v at_o it_o it_o shall_v appear_v on_o both_o side_n of_o d_o to_z a_o on_o the_o right_a side_n to_z b_o on_o the_o left_a side_n and_o this_o happen_v by_o double_v of_o d_o so_o that_o from_o hence_o this_o paradoxical_a corollary_n arise_v that_o a_o object_n may_v be_v see_v in_o two_o place_n and_o yet_o â—ot_n see_v double_a they_o that_o assert_v that_o we_o see_v but_o with_o one_o eye_n whilst_o the_o other_o be_v idle_a and_o do_v nothing_o assert_v likewise_o that_o all_o visual_a spirit_n recede_v from_o the_o idle_a eye_n and_o only_o supply_v the_o eye_n that_o see_v but_o i_o see_v no_o reason_n why_o the_o eye_n a_o b_o looking_z at_z c_o either_o of_o they_o shall_v be_v say_v destitute_a of_o spirit_n in_o respect_n of_o c_o which_o they_o see_v single_a and_o yet_o both_o replenish_v with_o spirit_n in_o respect_n of_o d_o which_o they_o see_v double_a the_o image_n of_o c_o and_o d_o both_o be_v paint_v on_o the_o retina_fw-la of_o a_o as_o well_o as_o of_o b_o and_o therefore_o a_o and_o b_o both_o be_v replenish_v with_o spirit_n to_o â—ee_z d_o even_o by_o the_o concession_n of_o our_o adversary_n why_o not_o to_o see_v c_o also_o at_o which_o they_o steadfast_o look_v appendix_n whilst_o this_o book_n be_v in_o the_o press_n my_o affair_n be_v such_o that_o i_o can_v not_o attend_v the_o perusal_n and_o correction_n thereof_o but_o therein_o have_v make_v use_n of_o my_o friend_n mr._n e._n halley_n who_o be_v willing_a to_o do_v i_o that_o service_n he_o after_o the_o first_o part_n hereof_o be_v finish_v send_v i_o a_o proposition_n of_o his_o own_o which_o i_o take_v to_o be_v of_o that_o
true_a respective_a focus_n but_o if_o we_o believe_v the_o say_v mons._n auzout_o by_o this_o way_n if_o this_o way_n which_o i_o propose_v be_v his_o as_o i_o know_v not_o whether_o it_o be_v or_o not_o one_o come_v near_o enough_o to_o exactness_n and_o perhaps_o as_o just_a as_o by_o most_o of_o the_o method_n ordinary_o use_v however_o though_o the_o practice_n through_o some_o accidental_a difficulty_n do_v not_o so_o exact_o answer_v the_o theory_n yet_o it_o can_v be_v deny_v that_o the_o theory_n be_v true_a and_o perhaps_o far_a improvement_n may_v bring_v it_o to_o perfection_n chap._n vii_o a_o optic_a problem_n of_o double_a vision_n in_o tab._n 4â—_n fig._n 1._o 〈◊〉_d a_o b_o be_v the_o two_o eye_n c_o the_o nigh_a object_n d_o the_o far_a object_n if_o both_o eye_n open_a be_v fix_v upon_o c_o the_o object_n d_o shall_v seem_v double_a and_o then_o shut_v the_o left_a eye_n a_o the_o left_a image_n of_o d_o disappear_v and_o shut_v the_o right_a eye_n b_o the_o right_a image_n of_o d_o disappear_v but_o if_o both_o eye_n open_a be_v fix_v on_o d_o then_z c_z shall_v seem_v double_a and_o if_o the_o left_a eye_n a_o be_v shut_v the_o right_a image_n of_o c_o vanish_v if_o the_o right_a eye_n b_o be_v shuâ—_n the_o left_a image_n of_o c_o vanishes_z this_o be_v the_o declaration_n of_o the_o phaenomenon_n which_o any_o one_o may_v experiment_n by_o place_v two_o candle_n d_o 3_o foot_n and_o c_o 1_o foot_n distant_a from_o the_o eye_n and_o then_o stand_v so_o that_o the_o nose_n and_o two_o object_n may_v lie_v in_o or_o near_o a_o right_a line_n he_o fix_v his_o eye_n on_o either_o object_n alternate_o open_a and_o shut_v they_o i_o choose_v two_o candle_n and_o at_o that_o distance_n and_o posture_n because_o the_o experiment_n thereby_o will_v be_v more_o sensible_o evident_a though_o it_o hold_v in_o any_o two_o object_n at_o whatever_o distance_n till_o the_o distance_n be_v so_o great_a that_o the_o interval_n between_o the_o two_o eye_n bear_v no_o sensible_a proportion_n thereto_o that_o be_v till_o the_o angle_n acb_n and_o much_o more_o a_o d_o b_o be_v so_o very_o small_a that_o the_o line_n ac_fw-la bc_n may_v be_v take_v to_o run_v as_o it_o be_v parallel_v this_o be_v declare_v i_o explicate_v the_o reason_n of_o this_o appearance_n as_o follow_v in_o the_o first_o case_n both_o eye_n be_v fix_v on_o c_o if_o the_o right_a eye_n b_o be_v shut_v the_o object_n d_o will_v appear_v to_o the_o left_a hand_n of_o c_o then_o shut_v the_o left_a eye_n a_o and_o open_v the_o right_a eye_n b_o and_o look_v at_o c_o d_o will_v appear_v to_o the_o right_a hand_n of_o c_o therefore_o open_v both_o a_o and_o b_o and_o look_v steadfast_o on_o c_o the_o object_n d_o will_v appear_v on_o both_o side_n c_o that_o be_v both_o to_o the_o right_n and_o left_a hand_n of_o c_o and_o therefore_o double_a and_o it_o be_v manifest_a the_o right_a eye_n b_o receive_v the_o right_a image_n of_o d_o and_o the_o left_a eye_n a_o the_o left_a image_n of_o d_o therefore_o in_o this_o case_n to_o the_o right_a eye_n be_v shut_v the_o right_a image_n of_o d_o disappear_v and_o to_o the_o left_a eye_n be_v shut_v the_o left_a image_n of_o d_o disappear_v but_o in_o the_o second_o case_n fix_v both_o eye_n on_o d_o c_o seem_v double_a for_o the_o left_a eye_n a_o be_v shut_v c_o appear_v to_o b_o on_o the_o left_a hand_n of_o d_o then_o the_o right_a eye_n be_v shut_v the_o left_a eye_n a_o see_v c_o on_o the_o right_a hand_n of_o d_o so_o that_o in_o this_o case_n the_o right_a eye_n receive_v the_o left_a image_n of_o c_o and_o the_o left_a eye_n the_o right_a image_n of_o c_o and_o consequent_o the_o open_n or_o shut_v of_o either_o do_v in_o this_o case_n make_v the_o contrary_a image_n of_o c_o disappear_z and_o why_o c_o shall_v seem_v double_a be_v plain_a in_o this_o case_n for_o the_o right_a eye_n see_v it_o on_o the_o left_a hand_n of_o d_o and_o the_o left_a eye_n on_o the_o right_a hand_n of_o d_o so_o that_o both_o eye_n see_v it_o on_o both_o hand_n of_o d_o and_o therefore_o double_a but_o then_o in_o the_o first_o case_n the_o object_n d_o and_o not_o the_o object_n c_o seem_v double_a and_o in_o the_o second_o case_n the_o object_n c_o and_o not_o the_o object_n d_o seem_v double_a for_o in_o vision_n there_o be_v a_o difference_n between_o look_v and_o see_v whatever_o object_n i_o look_v at_o with_o both_o eye_n appear_v single_a and_o all_o other_o more_o remote_a or_o nigh_o that_o i_o see_v appear_v double_a for_o upon_o the_o object_n i_o look_v at_o the_o optic_a axe_n do_v concur_v but_o not_o so_o on_o those_o i_o only_o see_v and_o this_o be_v the_o reason_n that_o at_o any_o time_n i_o can_v make_v all_o the_o object_n about_o i_o seem_v confuse_v only_o by_o turn_v the_o optic_a axe_n so_o that_o they_o may_v concur_v in_o the_o free_a air_n as_o if_o there_o be_v a_o certain_a visible_a object_n there_o before_o they_o though_o real_o there_o be_v none_o and_o that_o the_o concurrence_n of_o the_o axe_n optici_fw-la in_o a_o single_a point_n or_o object_n be_v sufficient_a to_o make_v that_o object_n seem_v but_o one_o beside_o the_o proof_n of_o the_o forego_n experiment_n i_o shall_v endeavour_v to_o evince_v or_o at_o least_o to_o explicate_v by_o a_o other_o know_v affection_n of_o vision_n the_o explanation_n whereof_o be_v allow_v by_o all_o man_n as_o satisfactory_a it_o be_v this_o in_o tab._n 41._o fig._n 2._o 4._o the_o image_n a_o b_o of_o the_o object_n a_o b_o be_v paint_v on_o the_o retina_fw-la invert_v and_o yet_o the_o eye_n or_o rather_o the_o soul_n by_o mean_n of_o the_o eye_n see_v the_o object_n erect_v and_o in_o its_o natural_a posture_n because_o the_o mind_n take_v no_o notice_n of_o what_o happen_v to_o the_o ray_n in_o the_o eye_n by_o refraction_n or_o decussation_n but_o in_o its_o direction_n towards_o the_o object_n it_o follow_v straight_o alongst_o the_o ray_n as_o they_o by_o their_o impulse_n and_o in_o their_o plain_a course_n lead_v it_o and_o consequent_o follow_v the_o ray_n a_o a_o it_o be_v direct_v straight_o to_o the_o upper_a part_n of_o the_o object_n and_o also_o follow_v the_o ray_n b_o b_o it_o be_v direct_v to_o the_o low_a part_n of_o the_o object_n and_o so_o of_o the_o rest_n for_o suppose_v the_o ball_n of_o the_o eye_n take_v out_o of_o its_o socket_n or_o cavity_n in_o the_o skull_n and_o a_o man_n receive_v in_o the_o socket_n a_o impulse_n by_o a_o stick_n come_v in_o the_o posture_n of_o b_o b_o and_o hit_v he_o on_o the_o upper_a part_n of_o the_o cavity_n sure_o he_o will_v never_o look_v for_o the_o original_a of_o this_o blow_n at_o a_o but_o will_v be_v certain_o direct_v to_o hunt_v back_o as_o it_o be_v alongst_o the_o stick_n b_o b_o towards_o the_o place_n from_o whence_o the_o stroke_n come_v so_o the_o mind_n do_v hunt_v back_o by_o mean_n of_o each_o pencil_n of_o ray_n which_o be_v as_o it_o be_v a_o stick_n give_v the_o retina_fw-la a_o certain_a impulse_n to_o the_o point_n from_o whence_o it_o come_v and_o be_v thereby_o direct_v straight_o thereto_o to_o apply_v this_o to_o what_o i_o intend_v i_o say_v then_o that_o the_o mind_n or_o visive_a faculty_n if_o i_o may_v have_v leave_n to_o use_v that_o word_n for_o a_o thing_n we_o all_o understand_v and_o can_v better_o express_v take_v no_o notice_n that_o there_o be_v two_o axe_n optici_fw-la or_o two_o picture_n make_v by_o those_o axe_n optici_fw-la on_o each_o retina_fw-la but_o follow_v back_o and_o hunt_v counter_a alongst_o these_o axe_n it_o be_v direct_v to_o and_o determine_v in_o one_o single_a point_n and_o therefore_o it_o see_v it_o as_o one_o and_o see_v this_o speculation_n do_v natural_o lead_v i_o to_o the_o consideration_n of_o a_o opinion_n first_o as_o i_o think_v start_v by_o the_o celebrate_v gassendus_fw-la and_o since_o embrace_v by_o many_o viz._n that_o we_o see_v but_o with_o one_o eye_n at_o once_o one_o and_o the_o same_o point_n of_o a_o object_n otiante_fw-la alio_fw-la as_o they_o term_v it_o whilst_o the_o other_o be_v idle_a and_o do_v nothing_o i_o shall_v not_o think_v it_o improper_a to_o subjoin_v to_o my_o former_a discourse_n something_o relate_v to_o that_o opinion_n confine_v myself_o only_o to_o what_o may_v something_o illustrate_v my_o former_a explanation_n for_o to_o enumerate_v all_o the_o experiment_n that_o prove_v we_o see_v with_o two_o eye_n will_v swell_v this_o far_o beyond_o the_o limit_n i_o design_v it_o therefore_o to_o the_o matter_n against_o our_o see_v with_o two_o eye_n at_o once_o one_o and_o the_o
we_o must_v consider_v that_o these_o labour_v under_o the_o contrary_a defect_n with_o old_a man_n for_o they_o see_v nigh_o object_n distinct_o but_o distant_a object_n confuse_o must_v be_v relieve_v with_o a_o remedy_n of_o a_o contrary_a effect_n and_o therefore_o they_o be_v help_v by_o concave-glass_n which_o bring_v the_o ray_n of_o distant_a object_n into_o the_o eye_n as_o if_o they_o be_v nigh_o and_o because_o we_o may_v conceive_v the_o crystallines_n of_o these_o eye_n as_o too_o protuberant_a or_o convex_a therefore_o we_o be_v to_o take_v off_o from_o this_o too_o great_a convexity_n by_o add_v a_o adventitious_a concavity_n but_o then_o there_o be_v nothing_o so_o universal_o complain_v of_o by_o those_o who_o be_v thus_o affect_v as_o the_o difficulty_n they_o find_v in_o fit_v proper_a glass_n to_o their_o eye_n for_o the_o removal_n whereof_o the_o follow_a rule_n may_v be_v observe_v first_o that_o for_o view_v distant_a object_n according_a to_o what_o be_v note_v 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to_o be_v receive_v by_o the_o eye_n of_o a_o myops_n so_o at_o the_o same_o time_n they_o diminish_v the_o appearance_n of_o the_o whole_a object_n and_o from_o hence_o it_o be_v that_o though_o these_o sort_n of_o eye_n may_v be_v well_o enough_o relieve_v for_o read_v and_o write_v at_o a_o convenient_a distance_n and_o for_o see_v pretty_a large_a object_n at_o the_o distance_n of_o 100_o 200_o or_o 500_o foot_n yet_o for_o object_n much_o far_o unless_o they_o be_v very_o large_a indeed_o they_o be_v not_o so_o easy_o supply_v 3._o and_o here_o i_o can_v but_o take_v notice_n of_o a_o ingenious_a intimation_n of_o mr._n hook_n consider_v to_o who_o the_o world_n be_v certain_o much_o oblige_v for_o his_o curious_a contrivance_n in_o mechanic_n and_o his_o other_o philosophic_a endeavour_n publish_v in_o num._n 3._o of_o the_o philosophical_a collection_n lond._n 1681._o which_o he_o call_v myopibus_fw-la juvamen_fw-la it_o be_v brief_o this_o that_o some_o sort_n of_o shortsighted_a person_n who_o can_v be_v relieve_v by_o concave_a glass_n may_v perhaps_o find_v some_o help_n in_o convex-glass_n their_o eye_n be_v remove_v at_o a_o convenient_a distance_n far_o from_o these_o glass_n than_o their_o distinct_a base_n as_o for_o read_v by_o these_o glass_n the_o book_n must_v be_v invert_v and_o then_o the_o image_n in_o the_o distinct_a base_a shall_v be_v erect_v and_o the_o eye_n shall_v perceive_v it_o erect_v as_o for_o write_v the_o difficulty_n be_v great_a than_o mention_v by_o the_o learned_a author_n for_o the_o myops_n must_v not_o only_o learn_v to_o write_v invert_v but_o also_o retrograde_a viz._n from_o the_o right_n to_o the_o left_a hand_n and_o what_o be_v yet_o more_o inconvenient_a from_o the_o bottom_n towards_o the_o top_n of_o the_o page_n which_o be_v hardly_o practicable_a on_o account_n of_o blot_v the_o wet_a write_n as_o for_o view_v distant_a object_n with_o these_o glass_n i_o acknowledge_v with_o the_o ingenious_a author_n that_o much_o of_o the_o disagreableness_n of_o the_o invert_v prospect_n be_v take_v off_o by_o use_n and_o custom_n as_o i_o myself_o have_v experience_v by_o my_o frequent_a use_n of_o invert_v telescope_n but_o yet_o i_o can_v go_v so_o far_o with_o the_o author_n as_o to_o assent_v to_o his_o deduction_n from_o hence_o which_o be_v that_o it_o be_v only_a use_n and_o custom_n that_o make_v we_o judge_v object_n erect_v that_o be_v perceive_v by_o a_o invert_v image_n on_o the_o fund_z of_o the_o eye_n for_o then_o a_o man_n stand_v on_o his_o head_n shall_v judge_v the_o tree_n and_o other_o object_n he_o see_v invert_v which_o no_o one_o in_o his_o sense_n will_v do_v but_o rather_o judge_v what_o be_v right_a viz._n that_o he_o himself_o be_v invert_v whilst_o the_o circumjacent_a object_n continue_v erect_v this_o will_v be_v more_o evident_a to_o we_o by_o consider_v the_o case_n of_o a_o adult_n person_n who_o have_v be_v blind_a from_o his_o birth_n and_o now_o sudden_o restore_v to_o his_o sight_n he_o be_v not_o prejudice_v by_o custom_n and_o yet_o doubtless_o will_v judge_v as_o be_v usual_a but_o last_o a_o other_o great_a difficulty_n that_o will_v attend_v the_o use_n of_o these_o spectacle_n for_o myopes_n be_v that_o they_o must_v be_v carry_v at_o such_o a_o distance_n from_o the_o eye_n that_o it_o will_v be_v very_o troublesome_a to_o manage_v they_o commodious_o and_o if_o to_o this_o again_o we_o add_v the_o distance_n requisite_a for_o the_o object_n i_o question_v whether_o some_o man_n arm_n will_v be_v long_o enough_o to_o manage_v a_o pen_n for_o write_v or_o turn_v the_o leave_v of_o a_o book_n i_o have_v be_v the_o long_o on_o this_o proposal_n because_o the_o worthy_a author_n do_v candid_o invite_v all_o to_o communicate_v to_o the_o public_a what_o real_a benefit_n by_o it_o or_o objection_n against_o it_o they_o shall_v find_v 4._o i_o shall_v conclude_v this_o chapter_n with_o the_o way_n of_o adapt_a telescope_n and_o microscope_n to_o defective_a eye_n eye_n which_o be_v briesly_a thus_o a_o telescope_n compose_v of_o a_o convex_a object-glass_n and_o concave_a eye-glass_n be_v apply_v to_o a_o old_a eye_n the_o eye-glass_n may_v be_v a_o little_a far_o remove_v from_o the_o object-glass_n than_o ordinary_o on_o the_o contrary_a in_o such_o a_o telescope_n for_o the_o eye_n of_o a_o myops_n the_o eye-glass_n may_v be_v remove_v a_o little_a nigh_o to_o the_o object-glass_n the_o reason_n hereof_o be_v manifest_a from_o what_o have_v be_v deliver_v in_o the_o first_o part._n but_o then_o how_o much_o far_o or_o nigh_o they_o be_v to_o be_v remove_v be_v only_o to_o be_v determine_v by_o experiment_n and_o by_o every_o one_o fit_v the_o glass_n to_o his_o own_o eye_n and_o so_o likewise_o in_o telescope_n compose_v of_o a_o convex_a object-glass_n and_o convex_a eye-glass_n for_o
more_o in_o this_o chapter_n be_v plain_a to_o lay_v down_o some_o practical_a rule_n for_o find_v the_o foci_fw-la and_o centre_n of_o glass_n with_o some_o other_o accidental_a remark_n that_o may_v be_v requisite_a to_o the_o clear_a understanding_n and_o performance_n of_o some_o precept_n deliver_v in_o this_o treatise_n the_o object-glass_n of_o telescope_n be_v general_o of_o so_o little_a curvity_n on_o their_o superficies_n that_o by_o look_v on_o they_o or_o by_o feel_v they_o it_o can_v be_v discover_v whether_o they_o be_v plain_a or_o of_o a_o spheric_a figure_n or_o which_o be_v form_v on_o a_o sphere_n of_o a_o great_a which_o of_o a_o lesser_a radius_fw-la to_o find_v this_o as_o i_o have_v say_v before_o in_o schol._n prop._n xxxi_o part_n i._o we_o be_v to_o shake_v the_o glass_n nimble_o at_o our_o arm_n length_n before_o the_o eye_n and_o if_o the_o object_n see_v through_o it_o seem_v to_o dance_v or_o move_v the_o glass_n be_v not_o plain_a and_o that_o glass_n which_o make_v the_o object_n seem_v the_o most_o to_o move_v be_v form_v on_o the_o less_o sphere_n whether_o convex_a or_o concave_a 3._o when_o we_o have_v thus_o find_v our_o glass_n to_o be_v spheric_a then_o suppose_v they_o convex_a glass_n there_o be_v several_a method_n for_o find_v their_o foci_fw-la i_o shall_v lay_v down_o some_o of_o the_o plain_a and_o most_o certain_a first_o for_o glass_n of_o pretty_a deep_a convexity_n that_o be_v of_o small_a sphere_n apply_v they_o to_o the_o end_n of_o a_o scale_n of_o inch_n and_o decimal_a part_n and_o expose_v they_o before_o the_o sun_n and_o upon_o the_o scale_n we_o shall_v find_v the_o bright_a intersection_n of_o the_o ray_n exact_o measure_v out_o or_o expose_v they_o in_o the_o hole_n of_o a_o dark_a chamber_n and_o where_o a_o white_a paper_n receive_v the_o distinct_a representation_n of_o distant_a object_n there_o be_v the_o focus_n of_o this_o glass_n this_o be_v a_o universal_a and_o certain_a way_n for_o all_o 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convexity_n turn_v from_o the_o sun_n and_o the_o second_o distance_n be_v about_o half_a the_o radius_fw-la of_o other_o convexity_n likewise_o thus_o we_o have_v the_o radii_fw-la of_o the_o two_o convexity_n whence_o the_o focus_n be_v determine_v by_o prop._n iii_o part_n i._o the_o reason_n hereof_o depend_v on_o the_o doctrine_n of_o catoptric_n but_o the_o most_o exact_a way_n of_o determine_v the_o just_a focal_a length_n of_o the_o object-glass_n of_o a_o telescope_n be_v what_o i_o shall_v lay_v down_o in_o chap._n v._o sec._n 4._o of_o this_o part_n which_o because_o i_o must_v necessary_o deliver_v in_o that_o place_n i_o will_v not_o here_o anticipate_v the_o foci_fw-la of_o concave_n be_v obtain_v by_o reflection_n concave_n for_o as_o a_o concave_a miroir_n or_o speculum_fw-la burn_v at_o the_o distance_n of_o about_o half_a the_o radius_fw-la of_o the_o concavity_n so_o a_o concave-glass_n be_v suppose_v a_o reflect_v speculum_fw-la shall_v unite_v the_o ray_n of_o the_o sun_n at_o the_o distance_n of_o about_o half_a the_o radius_fw-la of_o the_o cavity_n 4_o before_o we_o proceed_v to_o the_o centration_n of_o glass_n glass_n we_o be_v to_o recollect_v the_o 18_o definition_n of_o the_o first_o part_n wherein_o we_o define_v the_o axis_n of_o a_o glass_n i_o say_v therefore_o when_o the_o axis_n of_o a_o glass_n pass_v direct_o through_o the_o centre_n of_o the_o glass_n breadth_n or_o roundness_n of_o its_o aperture_n that_o glass_n be_v say_v to_o be_v true_o centre_v and_o this_o will_v always_o be_v so_o when_o the_o glass_n be_v equal_o thick_a round_o the_o edge_n of_o its_o aperture_n but_o this_o will_v be_v more_o intelligible_a by_o a_o scheme_n tab._n 40._o fig._n 1._o 1._o let_v a_o g_o d_o e_o a_o be_v a_o planoconvex_a glass_n much_o thick_a towards_o the_o edge_n d_o e_o than_o towards_o a_o let_v a_o g_o be_v equal_a to_z g_o d_o g_o be_v the_o centre_n of_o this_o glass_n for_o it_o be_v the_o middle_a point_n of_o its_o 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coincident_a with_o the_o middle_a point_n of_o its_o breadth_n or_o aperture_n we_o be_v to_o make_v k_o b_o equal_a to_o k_o d_o and_o then_o we_o be_v to_o cut_v off_o or_o to_o cover_v the_o portion_n of_o the_o glass_n b_o a_fw-fr c_o equal_a to_z d_o f_o e_o and_o so_o we_o obtain_v the_o complete_a and_o true_o centre_v glass_n c_o b_o k_o d_o e_o c._n the_o same_o may_v be_v understand_v of_o double_a convex_n without_o far_a explication_n but_o because_o in_o object-glass_n of_o even_o moderate_a length_n it_o be_v impossible_a by_o the_o eye_n or_o any_o admeasurement_n of_o their_o thickness_n to_o know_v whether_o they_o be_v true_o centre_v therefore_o we_o must_v have_v recourse_n to_o some_o other_o method_n that_o may_v show_v this_o and_o these_o be_v various_a first_o hold_v the_o glass_n at_o a_o due_a distance_n from_o the_o eye_n let_v we_o observe_v the_o two_o reflect_a image_n of_o a_o candle_n and_o where_o these_o two_o image_n unite_v or_o coalesce_v there_o be_v the_o true_a centre_n of_o the_o glass_n if_o this_o be_v in_o the_o middle_n of_o the_o glass_n breadth_n the_o glass_n be_v true_o centre_v if_o not_o we_o be_v to_o rectify_v it_o shall_v be_v declare_v hereafter_o a_o second_o way_n be_v by_o present_v the_o glass_n before_o the_o sun_n and_o make_v it_o reflect_v the_o light_n on_o a_o plain_a nighly_a parallel_n to_o its_o surface_n at_o a_o proper_a distance_n and_o we_o shall_v perceive_v two_o sort_n of_o light_n reflect_v one_o small_a but_o much_o more_o strong_a and_o vigorous_a within_o another_o more_o faint_a and_o large_a then_o by_o a_o due_a posture_n of_o the_o glass_n find_v by_o trial_n both_o these_o light_n be_v to_o be_v project_v as_o round_o as_o possible_a and_o at_o a_o proper_a distance_n from_o the_o wall_n on_o which_o they_o be_v reflect_v the_o round_o bright_a spot_n be_v to_o be_v bring_v into_o the_o small_a compass_n that_o it_o can_v trial_n will_v make_v all_o this_o plain_a when_o the_o glass_n be_v in_o this_o posture_n if_o the_o bright_a spot_n be_v project_v just_a in_o the_o middle_n of_o the_o faint_a light_n the_o glass_n be_v well_o centre_v if_o it_o be_v project_v to_o the_o left_a hand_n of_o this_o middle_n the_o glass_n be_v thick_a towards_o the_o left_a hand_n edge_n and_o so_o to_o whatever_o side_n of_o the_o faint_a light_n this_o bright_a spot_n be_v project_v on_o that_o side_n be_v the_o glass_n thick_a and_o on_o that_o side_n lie_v the_o true_a centre_n the_o reason_n hereof_o i_o shall_v explain_v in_o a_o plano-convex-glass_n and_o be_v the_o same_o in_o a_o double_a convex_a mutatis_fw-la mutandis_fw-la for_o the_o bright_a spot_n be_v the_o image_n of_o the_o sun_n
hevelius_n and_o hook_n concern_v telescopic_a sight_n 2._o hevelius_n objection_n against_o they_o his_o mistake_n concern_v they_o 3._o their_o fabric_n or_o contrivance_n 4._o adjust_v they_o to_o plain_a ruler_n or_o tube_n 5._o to_o quadrant_n sextant_n etc._n etc._n 6._o dioptrick_n reason_n of_o their_o performance_n 7._o adapt_a the_o micrometre_n to_o a_o telescope_n 1_o the_o fame_n of_o johannes_n hevelius_n telescopick-sight_n consul_n of_o dantzick_n be_v deserve_o celebrate_v by_o all_o that_o delight_n in_o astronomy_n his_o performance_n herein_o be_v high_o extol_v by_o all_o and_o the_o sumptuous_a volume_n of_o his_o labour_n and_o study_n which_o he_o have_v publish_v have_v procure_v he_o a_o immortal_a name_n of_o honour_n among_o the_o literate_a but_o notwithstanding_o all_o his_o commendable_a endeavour_n he_o have_v not_o yet_o arrive_v at_o the_o height_n of_o perfection_n but_o something_o be_v yet_o want_v and_o deficient_a even_o in_o his_o most_o costly_a machine_n whoever_o peruse_v the_o large_a and_o elegant_a volume_n of_o his_o first_o machina_fw-la coelestibus_fw-la will_v admire_v at_o the_o vast_a treasure_n he_o have_v expend_v on_o astronomical_a instrument_n of_o all_o sort_n when_o he_o see_v even_o the_o very_a description_n of_o they_o so_o very_o sumptuous_a and_o yet_o at_o the_o same_o time_n whoever_o peruse_v a_o small_a book_n of_o animadversion_n on_o this_o machina_fw-la coelestibus_fw-la â—by_o the_o ingenious_a mr._n hook_n will_v find_v one_o grand_a defect_n do_v attend_v the_o noble_a hevelius_n instrument_n which_o render_v they_o i_o will_v not_o say_v useless_a faulty_a or_o no_o better_a than_o ticho_n yet_o not_o so_o complete_a and_o perfect_a as_o otherwise_o they_o have_v be_v by_o the_o addition_n of_o telescopic_a sight_n for_o hevelius_n whole_o use_v plain_a sight_n which_o certain_o be_v not_o so_o accurate_a as_o telescopick_n and_o though_o i_o must_v confess_v ingenious_o that_o this_o renown_v astronomer_n by_o his_o extraordinary_a diligence_n great_a care_n and_o perpetual_a long-continued_a practice_n but_o chief_o by_o his_o peculiar_a sharpness_n of_o sight_n have_v arrive_v to_o a_o great_a exactness_n of_o observation_n by_o plain_a sight_n as_o i_o find_v by_o compare_v the_o observation_n make_v by_o the_o most_o curious_a astronomer_n of_o our_o age_n flamsteed_o halley_n cassin_n etc._n etc._n by_o telescopic_a sight_n with_o those_o observation_n make_v by_o hevelius_n yet_o this_o we_o be_v to_o attribute_v more_o to_o the_o peculiar_a acuteness_n of_o his_o eye_n and_o to_o his_o extraordinary_a diligence_n and_o care_n in_o observation_n than_o to_o the_o exactness_n of_o plain_a sight_n for_o to_o i_o it_o seem_v manifest_a from_o what_o the_o learned_a mr._n hook_n lay_v down_o in_o the_o forementioned_a book_n that_o the_o naked_a eye_n can_v ordinary_o perceive_v a_o angle_n or_o object_n that_o subtend_v a_o angle_n less_o than_o a_o minute_n or_o half_o a_o minute_n at_o the_o small_a for_o though_o we_o perceive_v star_n of_o that_o magnitude_n that_o their_o diameter_n be_v not_o half_a a_o minute_n yet_o this_o be_v by_o a_o sort_n of_o adventitious_a or_o glare_a light_n that_o be_v cause_v by_o the_o refraction_n of_o their_o ray_n in_o the_o air_n which_o make_v they_o appear_v to_o we_o much_o big_a than_o real_o they_o be_v as_o be_v manifest_a when_o we_o come_v to_o look_v at_o they_o with_o a_o telescope_n that_o take_v off_o this_o glare_a light_n 2._o the_o want_n therefore_o of_o telescopic_a sight_n be_v what_o mr._n hook_v chief_o insist_o upon_o as_o defective_a in_o hevelius_n they_o costly_a astronomical_a apparatus_fw-la but_o yet_o in_o his_o whole_a book_n of_o animadversion_n he_o take_v no_o notice_n of_o the_o chief_a objection_n which_o hevelius_n use_v against_o they_o and_o i_o be_o persuade_v the_o candour_n of_o that_o noble_a astronomer_n who_o memory_n must_v now_o be_v sacred_a be_v so_o great_a that_o upon_o the_o removal_n of_o these_o difficulty_n he_o will_v have_v give_v up_o the_o cause_n for_o it_o seem_v the_o controversy_n be_v long_o agitate_a between_o they_o these_o objection_n we_o shall_v find_v in_o the_o first_o part_n of_o the_o machina_fw-la coelestibus_fw-la ap_fw-mi fourteen_o pag._n 296._o accedit_fw-la si_fw-la quando_fw-la observator_fw-la non_fw-la aequè_fw-la directè_fw-la &_o precisè_fw-la semper_fw-la ut_fw-la saepius_fw-la crede_fw-la contingeret_fw-la per_fw-la centra_fw-la lentium_fw-la collineat_fw-la facile_fw-la diversitas_fw-la aliqua_fw-la aspectûs_fw-la observationibus_fw-la possit_fw-la induci_fw-la quae_fw-la svo_fw-la tempore_fw-la coeli_fw-la scrutatores_fw-la jugiter_fw-la seduceret_fw-la caeterum_fw-la cum_fw-la acus_fw-la vel_fw-la fila_fw-la adeo_fw-la prope_fw-la lentem_fw-la ocularem_fw-la ad_fw-la observatoris_fw-la oculum_fw-la vix_fw-la in_o remotione_fw-la aliquot_fw-la digitorum_fw-la subsistunt_fw-la dubito_fw-la a_fw-mi dioptra_fw-la haec_fw-la oculo_fw-la tam_fw-la propanqua_fw-la multo_fw-la accuratius_fw-la stellas_fw-la quasvis_fw-la minimas_fw-la quam_fw-la pinnacidia_n nostra_fw-la ad_fw-la â—ex_fw-la novemve_fw-la pedes_fw-la ab_fw-la inuicem_fw-la remota_fw-la possit_fw-la detegere_fw-la nam_fw-la etiamsi_fw-la objectum_fw-la distinctius_fw-la videas_fw-la in_fw-la eo_fw-la tamen_fw-la quod_fw-la dioptra_fw-la tua_fw-la oculo_fw-la propius_fw-la adheret_fw-la plus_fw-la à _fw-la vero_fw-la deflectere_fw-la poteris_fw-la quam_fw-la nos_fw-la circa_fw-la nostra_fw-la pinnacidia_n quae_fw-la tanto_fw-la spatio_fw-la ab_fw-la inuicem_fw-la removentar_fw-la ut_fw-la taceam_fw-la quod_fw-la intersectio_fw-la filorum_fw-la minimas_fw-la stellas_fw-la tibi_fw-la tegat_fw-la etc._n etc._n for_o english_a reader_n thus_o add_v to_o this_o that_o if_o at_o any_o time_n the_o observator_fw-la chance_v not_o to_o look_v direct_o and_o precise_o through_o the_o midst_n of_o the_o glass_n as_o believe_v i_o it_o may_v often_o happen_v some_o variety_n may_v easy_o intermingle_v with_o the_o observation_n which_o in_o time_n may_v egregious_o deceive_v the_o astronomer_n moreover_o see_v the_o needle_n or_o cross_a thread_n do_v stand_v so_o close_o to_o the_o eye-glass_n and_o near_o the_o eye_n of_o the_o observator_fw-la i_o question_v whether_o these_o sight_n so_o near_o the_o eye_n can_v discover_v the_o small_a star_n much_o more_o accurate_o than_o our_o plain_a sight_n which_o be_v distant_a from_o each_o other_o six_o or_o nine_o foot_n for_o though_o by_o these_o telescopic_a sight_n one_o may_v see_v the_o object_n more_o distinct_o yet_o because_o they_o be_v so_o nigh_o to_o the_o eye_n one_o may_v err_v more_o than_o â—tis_o possible_a by_o our_o plain_a sight_n that_o be_v so_o far_o asunder_o so_o that_o i_o shall_v take_v no_o far_o notice_n of_o another_o inconvenience_n which_o be_v that_o the_o intersection_n of_o the_o thread_n shall_v cover_v the_o small_a star_n from_o your_o sight_n that_o hevelius_n do_v not_o right_o apprehend_v the_o nature_n of_o telescopic_a sight_n be_v manifest_a by_o this_o objection_n which_o he_o make_v against_o they_o from_o the_o shortness_n of_o the_o line_n of_o collimation_n which_o he_o imagine_v no_o long_o than_o between_o the_o eye_n or_o eye-glass_n and_o cross_a hair_n but_o be_v real_o as_o long_o as_o between_o the_o object-glass_n and_o cross_a hair_n as_o shall_v be_v evident_a from_o what_o i_o shall_v now_o lay_v down_o wherein_o i_o shall_v brief_o explain_v their_o usual_a fabric_n or_o contrivance_n their_o adjust_n to_o a_o plain_a ruler_n cylindrick_n or_o square_a tube_n their_o adjust_n to_o quadrant_n sextant_n and_o other_o instrument_n and_o the_o dioptrick_a reason_n of_o their_o performance_n and_o exactness_n 3._o and_o first_o the_o fabric_n or_o contrivance_n of_o these_o telescopic_a sight_n be_v brief_o thus_o tab._n 39_o fig._n 1._o 1._o choose_v a_o object-glass_n g_o c_o l_o and_o convex-eye-glass_n o_o p_o proper_a for_o the_o length_n of_o the_o ruler_n or_o tubeâ—_n g_o o_fw-fr p_o l_o which_o we_o be_v to_o use_v let_v we_o take_v care_n that_o the_o object-glass_n be_v pretty_a well_o centre_v by_o chap._n requisite_a 4._o sect._n 4_o of_o this_o part_n but_o in_o this_o particular_a the_o great_a exactness_n be_v not_o requisite_a whatever_o pere_n cherubin_n dâ—orleans_n may_v say_v to_o the_o contrary_a in_o the_o second_o tome_n of_o his_o vision_n parfait_n paris_n 1681._o fol._n in_o his_o description_n of_o level_n pag._n 23_o 81_o 106_o 108_o 109_o etc._n etc._n but_o chief_o pag._n 107._o wherein_o the_o friar_n be_v most_o gross_o mistake_v it_o be_v sufficient_a if_o the_o glass_n be_v pretty_a nigh_o the_o matter_n as_o usual_o most_o glass_n be_v immediate_o out_o of_o the_o workman_n hand_n this_o object-glass_n and_o eye-glass_n be_v each_o to_o be_v fix_v strong_o on_o a_o brass_n ring_n in_o the_o ruler_n at_o their_o proper_a distance_n and_o exact_o in_o the_o focus_n of_o the_o object-glass_n f_o m_o d_o i_o in_o a_o other_o brass_n ring_n be_v strain_v the_o fine_a cross-hair_n f_o d_o i_z m_z this_o ring_n be_v contrive_v to_o be_v movable_a to_o the_o right_n and_o left_a hand_n towards_z f_z or_o towards_z d_o and_o also_o if_o the_o
this_o manner_n 3._o tab._n 39_o fig._n 3._o on_o a_o even_a board_n draw_v the_o right_a line_n d_o h_o i_o b_o let_v a_o b_o c_o d_o be_v a_o ruler_n to_o which_o the_o telescopic_a sght_n be_v to_o be_v fit_v e_o the_o ring_n carry_v the_o object-glass_n f_o the_o ring_n carry_v the_o cross-hair_n g_z the_o snout_z carrying_z the_o eye-glass_n to_o the_o line_n b_o d_o apply_v the_o side_n b_o d_o of_o the_o ruler_n and_o look_v through_o the_o glass_n observe_v the_o point_n in_o a_o object_n distant_a a_o mile_n or_o two_o whereon_o the_o cross-hair_n fall_v then_o remove_v the_o ruler_n and_o apply_v its_o other_o side_n ac_fw-la to_o the_o line_n bd_o and_o observe_v whether_o the_o cross-hair_n fall_v on_o the_o same_o point_n of_o the_o object_n as_o before_o if_o they_o do_v so_o then_o be_v the_o side_n of_o the_o ruler_n a_o c_o b_o d_o parallel_n if_o noâ—_n than_o the_o side_n be_v not_o parallel_v the_o reason_n that_o so_o remote_a a_o object_n mâ—st_v be_v choose_v be_v that_o the_o breadth_n of_o the_o ruler_n may_v subtend_v a_o imperceptible_a angle_n in_o a_o circle_n who_o radius_fw-la be_v the_o distance_n of_o the_o object_n from_o the_o object-glass_n or_o otherwise_o in_o the_o plain_a board_n strike_v two_o round_a brass-wire_n pinn_v suppose_v h_n i_o which_o have_v their_o roundness_n from_o their_o be_v draw_v must_v needs_o have_v their_o side_n parallel_v to_o these_o pin_n apply_v one_o and_o to_o other_o side_n of_o the_o ruler_n and_o observe_v as_o before_o have_v thus_o find_v or_o make_v the_o two_o side_n of_o the_o ruler_n or_o four_o side_n of_o the_o tube_n if_o need_v be_v parallel_n the_o next_o thing_n be_v to_o make_v the_o line_n of_o collimation_n l_o k_n parallel_n to_o these_o side_n or_o to_o bring_v the_o intersection_n of_o the_o cross-hair_n e_o to_o meet_v with_o the_o axis_n lk_v of_o some_o of_o the_o radious_a pencil_n which_o axis_n after_o pass_v the_o object-glass_n run_v parallel_n to_o these_o side_n to_o effect_v this_o tab._n 39_o f._n 4_o 5_o 5_o we_o be_v to_o raise_v the_o plain_a board_n a_o b_o edgwife_n on_o the_o board_n of_o a_o window_n or_o table_n cd_o so_o that_o we_o may_v rest_v or_o sustain_v the_o ruler_n or_o parallelipiped_a tube_n a_o b_o c_o d_o e_o f_o g_o h_o on_o the_o round_a pin_n i_o k_o then_o look_v through_o the_o hole_n in_o the_o end_n g_o h_o d_o c_o design_v for_o the_o eye_n let_v we_o observe_v the_o point_n in_o a_o far_o distant_a object_n which_o fall_v exact_o on_o the_o intersection_n of_o the_o cross-hair_n afterward_o let_v we_o invert_v the_o ruler_n or_o tube_n as_o we_o have_v it_o in_o fig._n 5._o make_v the_o side_n a_o b_o c_o d_o which_o in_o fig._n 4._o be_v uppermost_a now_o undermost_a in_o this_o fig._n 5._o by_o which_o mean_n the_o side_n of_o the_o tube_n a_o d_o h_o e_o which_o in_o fig._n 4._o be_v far_a from_o the_o board_n in_o fig._n 5._o be_v next_o the_o board_n then_o look_v through_o the_o tube_n let_v we_o observe_v whether_o the_o cross-hair_n fall_v now_o on_o the_o same_o point_n in_o the_o object_n as_o in_o the_o first_o posture_n if_o they_o do_v agree_v exact_o then_o be_v the_o line_n of_o collimation_n parallel_v to_o the_o side_n a_o h_o b_o g_o if_o they_o do_v not_o but_o fall_v to_o the_o right_a hand_n apparent_o of_o the_o say_a point_n in_o the_o object_n then_o be_v the_o cross-hair_n to_o be_v remove_v by_o whatever_o contrivance_n they_o be_v make_v movable_a to_o the_o left_a hand_n the_o contrary_n require_v the_o contrary_a so_o that_o the_o tube_n continue_v in_o this_o latter_a posture_n the_o cross-hair_n may_v cover_v a_o point_n in_o the_o object_n middle_a between_o the_o point_n cover_v in_o the_o posture_n of_o fig._n 4._o and_o in_o the_o posture_n of_o fig._n 5._o at_o the_o first_o sight_n and_o thus_o by_o frequent_a repetition_n and_o trial_n we_o at_o last_o bring_v all_o to_o right_n after_o the_o same_o manner_n that_o we_o have_v rectify_v the_o line_n of_o collimation_n to_o run_v parallel_n to_o any_o two_o parallel_a side_n of_o the_o tube_n we_o may_v rectify_v it_o to_o a_o parallelism_n with_o the_o other_o two_o parallel_a side_n of_o the_o tube_n suppose_v the_o ring_n that_o carrier_n the_o cross-hair_n to_o have_v all_o the_o motion_n requisite_a to_o such_o rectification_n and_o so_o we_o fix_v all_o strong_o chief_o the_o object-glass_n and_o cross-hair_n and_o the_o operation_n be_v complete_a by_o this_o method_n the_o line_n of_o sight_n of_o any_o cylindrick_n or_o square_a tube_n may_v be_v make_v to_o run_v parallel_n to_o its_o side_n for_o many_o operation_n and_o observation_n mathematical_a and_o natural_a among_o other_o for_o find_v the_o declination_n of_o the_o magnet_n according_a to_o the_o method_n late_o propose_v by_o mons._n hautefeville_n and_o m._n sturmius_fw-la mistake_v in_o the_o journal_n des_fw-fr scavans_n 23._o aug._n 1683._o and_o in_o the_o acta_fw-la eruditorum_fw-la lipsie_n ann._n 1684._o decemb._n and_o for_o want_v of_o this_o method_n what_o mons._n sturmius_fw-la say_v in_o the_o aforesaid_a act._n li_n pag._n 579._o be_v very_o defective_a for_o thus_o he_o sola_o tubi_n locatio_fw-la ut_fw-la axis_n visionis_fw-la per_fw-la medias_fw-la lentes_n excurrens_fw-la meridianae_fw-la lineae_fw-la exact_v respondeat_fw-la difficulty_n quippiam_fw-la habere_fw-la videbatur_fw-la verum_fw-la &_o huic_fw-la infirmitati_fw-la praesens_fw-la uti_fw-la credo_fw-la inventum_fw-la est_fw-la remedium_fw-la etc._n etc._n and_o the_o remedy_n he_o tell_v we_o be_v that_o the_o tube_n be_v make_v a_o parallelipped_a of_o wood_n or_o brass_n for_o then_o say_v he_o apply_v the_o side_n of_o your_o tube_n to_o the_o meridian_n line_n the_o axis_n of_o vision_n will_v be_v parallel_n to_o the_o say_a meridian_n line_n but_o with_o the_o leave_v of_o so_o great_a a_o man_n i_o deny_v this_o unless_o first_o it_o be_v rectify_v so_o that_o this_o axis_n run_v parallel_v to_o the_o side_n of_o the_o tube_n and_o let_v we_o take_v what_o care_n soever_o possible_a for_o true_o centre_v the_o object-glass_n and_o place_v it_o and_o the_o cross-hair_n exact_o in_o the_o tube_n we_o must_v after_o all_o rectify_v these_o sight_n by_o some_o such_o method_n as_o i_o have_v lay_v down_o or_o else_o we_o may_v be_v egregious_o deceive_v and_o on_o this_o account_n error_n all_o the_o level_n and_o instrument_n to_o which_o pere_n cherubin_n d'orleans_n have_v adapt_v telescopick-sight_n and_o which_o he_o have_v so_o neat_o and_o sumptuous_o describe_v by_o curious_a scheme_n and_o a_o large_a volume_n la_fw-fr vision_n parfait_n tome_n ii_o a_o paris_n 1681._o fol._n be_v deficient_a and_o useless_a for_o he_o place_v the_o whole_a rectification_n of_o this_o line_n of_o collimation_n in_o the_o true_a centration_n of_o the_o glass_n pag._n 107._o and_o reject_v the_o right_a rectification_n by_o move_v of_o the_o cross-hair_n as_o erroneous_a pag._n 170._o but_o in_o this_o the_o friar_n betray_v his_o ignorance_n for_o though_o the_o true_a centration_n of_o the_o object-glass_n be_v of_o good_a convenience_n and_o advantage_n yet_o it_o do_v not_o perfect_a the_o instrument_n without_o far_a rectification_n as_o be_v impossible_a to_o be_v obtain_v to_o sufficient_a accuracy_n and_o therefore_o we_o must_v have_v recourse_n to_o some_o such_o method_n as_o forego_v i_o have_v hitherto_o mention_v only_o two_o of_o the_o fine_a cross-hair_n to_o be_v extend_v as_o a_o mensurator_n in_o the_o focus_n of_o the_o object-glass_n but_o for_o some_o use_v perhaps_o the_o fine_a silver_n or_o gold_n wire_n be_v better_a as_o not_o be_v disorder_v by_o heat_n and_o cold_a or_o else_o chapter_n the_o point_n of_o the_o small_a and_o most_o curious_a needle_n on_o who_o extremity_n the_o small_a telescopick-star_n may_v be_v visible_a when_o these_o telescopic_a sight_n telescopick-sight_n be_v right_o adjust_v in_o the_o tube_n and_o strong_o fix_v in_o their_o due_a posture_n by_o screw_n and_o all_o cover_v over_o from_o outward_a injury_n and_o accident_n they_o be_v of_o all_o sight_n the_o most_o constant_a and_o last_a and_o the_o least_o subject_a to_o be_v disorder_v so_o that_o when_o one_o find_v the_o great_a hevelius_n object_v against_o they_o their_o aptness_n to_o be_v out_o of_o order_n one_o will_v think_v the_o most_o commodious_a fabric_n of_o they_o be_v never_o explain_v to_o he_o though_o i_o be_o sure_a his_o instructor_n mr._n hook_n be_v as_o able_a as_o any_o in_o the_o world_n to_o inform_v he_o right_o in_o this_o matter_n 5._o i_o come_v now_o to_o the_o rectification_n of_o these_o sight_n on_o quadrant_n and_o sextant_n &c_n for_o take_v angle_n this_o be_v do_v either_o before_o or_o after_o the_o division_n into_o degree_n etc._n etc._n be_v make_v on_o the_o