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be_v a_o very_a great_a unhappiness_n to_o hevelius_n that_o he_o be_v not_o furnish_v with_o better_a contrivance_n yet_o it_o no_o way_n tend_v to_o his_o dispraise_n for_o his_o most_o extraordinary_a and_o indefatigable_a care_n pain_n and_o industry_n be_v so_o much_o the_o more_o to_o be_v admire_v esteem_v and_o honour_v and_o will_v be_v so_o much_o the_o more_o by_o such_o as_o have_v by_o experience_n find_v the_o difficulty_n of_o make_v any_o one_o observation_n certain_a in_o that_o way_n but_o that_o he_o or_o any_o other_o that_o have_v a_o mind_n to_o make_v further_a trial_n and_o observation_n may_v be_v free_v from_o this_o intolerable_a trouble_n and_o difficulty_n i_o have_v think_v of_o this_o follow_a instrument_n by_o mean_n whereof_o the_o quadrant_n be_v once_o adjust_v and_o
whereby_o distant_a place_n sometime_o appear_v and_o sometime_o disappear_v under_o the_o horizon_n by_o this_o mean_n also_o the_o rotundity_n of_o the_o earth_n may_v be_v true_o find_v vast_o surpass_v any_o thing_n perform_v by_o the_o best_a level_n yet_o know_v to_o this_o we_o may_v add_v the_o height_n of_o hill_n if_o their_o distance_n be_v know_v or_o their_o distance_n if_o their_o height_n be_v know_v i_o can_v have_v enlarge_v upon_o these_o and_o have_v name_v divers_a other_o but_o design_v it_o only_o as_o a_o answer_n to_o such_o as_o may_v captious_o put_v such_o a_o question_n i_o shall_v rather_o leave_v the_o pleasure_n of_o find_v they_o to_o such_o as_o shall_v real_o seek_v they_o to_o be_v assist_v thereby_o in_o their_o own_o undertake_n finis_fw-la errata_fw-la pag._n 2._o l._n 13._o r._n 9_o 10_o p._n 6._o l._n 14._o r._n aquilae_fw-la p._n 13._o l._n 3._o r._n mathematician_n p._n 15._o l._n 11._o r._n fig._n 32._o p._n 13._o l._n 28._o r._n fig._n 31._o p._n 18._o l._n 39_o r._n structuram_fw-la p._n 21._o l._n 26._o r._n dena_fw-la minuta_fw-la p._n 21._o l._n 27._o r._n discriminatim_fw-la p._n 22._o l._n 3._o r._n fig._n 35._o p._n 28._o l._n 34._o r._n quaedam_fw-la p._n 32._o l._n 21._o r._n shake_v p._n 33._o l._n 8._o r._n focus_fw-la p._n 39_o l._n 28._o r._n res_fw-la p._n 40._o l._n 11._o r._n admaveant_n p._n 40._o l._n 39_o deal_n se_fw-la a_o description_n of_o helioscope_n and_o some_o other_o instrument_n make_v by_o robert_n hooke_n fellow_n of_o the_o royal_a society_n hos_fw-la ego_fw-la etc._n etc._n sic_fw-la vos_fw-la non_fw-la vobis_fw-la london_n print_v by_o t._n r._n for_o john_n martin_n printer_n to_o the_o royal_a society_n at_o the_o bell_n in_o st._n paul_n churchyard_n 1676._o a_o description_n of_o helioscope_n and_o some_o other_o instrument_n the_o necessary_a avocation_n of_o business_n and_o the_o urgent_a importunity_n of_o some_o for_o the_o speedy_a publication_n of_o my_o animadversion_n make_v i_o conclude_v they_o in_o the_o eleven_o sheet_n without_o stay_v to_o explicate_v several_a thing_n which_o i_o design_v to_o go_v along_o with_o they_o but_o have_v now_o retrieve_v a_o little_a more_o of_o leisure_n both_o for_o delineation_n and_o description_n for_o a_o further_a elucidation_n of_o what_o i_o have_v say_v i_o shall_v make_v it_o my_o three_o attempt_n to_o explain_v first_o a_o helioscope_n to_o look_v upon_o the_o body_n of_o the_o sun_n without_o any_o offence_n to_o the_o observer_n eye_n second_o a_o way_n of_o shorten_v reflective_a and_o refractive_a telescope_n three_o a_o way_n for_o use_v a_o glass_n of_o any_o length_n without_o move_v the_o tube_n four_o a_o instrument_n for_o take_v the_o diameter_n of_o the_o sun_n moon_n and_o planet_n or_o for_o take_v any_o other_o distance_n to_o five_o or_o ten_o degree_n to_o the_o certainty_n of_o a_o second_o two_o of_o these_o i_o promise_v in_o the_o 78th_o or_o last_o page_n of_o my_o animadversion_n and_o the_o other_o fall_n in_o as_o analogous_fw-la to_o they_o five_o a_o instrument_n for_o describe_v all_o manner_n of_o dial_n by_o the_o tangent_fw-la projection_n six_o the_o use_n thereof_o 1._o for_o adjust_v the_o hand_n of_o a_o clock_n so_o as_o to_o make_v it_o move_v in_o the_o shadow_n of_o a_o dial_n who_o style_n be_v parallel_n to_o the_o axis_n or_o 2._o in_o the_o azimuth_n of_o any_o celestial_a body_n that_o be_v in_o the_o shadow_n of_o a_o upright_a or_o any_o other_o way_n incline_v style_n upon_o any_o plain_a 3._o for_o make_v a_o hand_n move_v according_a to_o the_o true_a aequation_n of_o time_n 4._o for_o make_v all_o manner_n of_o elliptical_a dial_n in_o mr._n foster_n '_o be_v way_n etc._n etc._n 5._o for_o communicate_v a_o circular_a motion_n in_o a_o curve_v line_n without_o any_o shake_n and_o for_o divers_a other_o excellent_a purpose_n and_o first_o for_o a_o helioscope_n which_o shall_v so_o take_v off_o the_o brightness_n of_o the_o sun_n as_o that_o the_o weak_a eye_n may_v look_v upon_o it_o at_o any_o time_n without_o the_o least_o offence_n my_o contrivance_n be_v by_o often_o reflect_v the_o ray_n from_o the_o surface_v of_o black_a glass_n which_o be_v ground_n very_o exact_o flat_a and_o very_o well_o polish_v so_o to_o diminish_v the_o radiation_n that_o at_o length_n they_o become_v as_o weak_a and_o faint_a as_o those_o of_o the_o moon_n in_o the_o twilight_n so_o that_o one_o may_v with_o ease_n and_o very_o much_o pleasure_n view_n examine_v and_o describe_v the_o phase_n of_o the_o sun_n and_o the_o maculae_fw-la and_o faculae_fw-la thereof_o if_o any_o such_o happen_v to_o appear_v when_o the_o observation_n be_v make_v and_o it_o give_v a_o good_a opportunity_n of_o discover_v they_o before_o we_o have_v any_o advertisement_n thereof_o from_o other_o the_o reason_n of_o which_o will_v be_v sufficient_o plain_a to_o such_o as_o consider_v how_o great_a a_o quantity_n of_o the_o ray_n of_o light_n be_v lose_v by_o every_o reflection_n and_o that_o every_o reflection_n do_v duplicate_v triplicate_v quadruplicate_v quintuplicate_v etc._n etc._n the_o first_o proportion_n of_o loss_n for_o instance_n suppose_v i_o have_v a_o helioscope_n make_v of_o a_o object_n glass_n a_o eye_n glass_n and_o four_o reflect_v glass_n and_o that_o by_o the_o first_o reflection_n i_o lose_v ¾_n of_o the_o direct_a light_n i_o affirm_v there_o will_v remain_v but_o 1_o 256_o part_n of_o the_o direct_a ray_n of_o the_o sun_n which_o can_v fall_v upon_o the_o eye_n at_o the_o last_o for_o if_o every_o reflection_n do_v lose_v ¾_n of_o its_o ray_n and_o reflect_v but_o ¼_n and_o that_o quarter_n lose_v ¾_n and_o reflect_v only_a ¼_n of_o its_o receive_a light_n there_o will_v remain_v but_o 1_o 16_o part_n of_o the_o whole_a and_o if_o this_o sixteenth_o part_n lose_v three_o quarter_n of_o its_o ray_n and_o reflect_v only_o a_o four_o it_o will_v follow_v the_o remainder_n will_v only_o be_v 1_o 64_o part_n of_o the_o whole_a and_o if_o that_o be_v once_o more_o reflect_v the_o ray_n will_v return_v but_o with_o 1_o 2â—6_n part_n of_o its_o first_o light_n this_o although_o it_o be_v obvious_a and_o easy_a enough_o now_o it_o be_v know_v yet_o i_o do_v not_o find_v that_o any_o person_n have_v yet_o have_v thought_n of_o apply_v it_o to_o this_o use_n the_o generality_n of_o observer_n have_v hitherto_o make_v use_n of_o either_o some_o very_a opacous_a and_o thick_a glass_n next_o the_o eye_n whether_o of_o red_a green_a blue_a or_o purple_a glass_n other_o have_v diminish_v the_o radiation_n by_o cover_v the_o glass_n with_o a_o very_a thick_a and_o close_a coat_n of_o the_o soot_n of_o a_o lamp_n other_o by_o cast_v the_o figure_n upon_o a_o piece_n of_o white_a paper_n whence_o it_o be_v reflect_v to_o the_o eye_n other_o have_v contract_v the_o aperture_n into_o a_o less_o circle_n and_o thereby_o let_v in_o less_o light_n and_o so_o make_v use_n of_o one_o single_a ray_n instead_o of_o a_o pencil_n of_o ray_n other_o have_v expanded_a the_o figure_n of_o the_o sun_n by_o the_o help_n of_o eye_n glass_n into_o a_o circle_n of_o ten_o twenty_o or_o a_o hundred_o time_n its_o diameter_n but_o none_o of_o all_o these_o way_n do_v come_v near_o this_o which_o i_o now_o describe_v by_o the_o help_n of_o three_o four_o or_o more_o reflection_n as_o any_o one_o upon_o trial_n will_v very_o plain_o discover_v first_o as_o to_o the_o colour_a glass_n i_o can_v at_o all_o approve_v of_o they_o because_o they_o thing_fw-mi the_o ray_n into_o the_o same_o colour_n and_o consequent_o take_v off_o the_o truth_n of_o the_o appearance_n as_o to_o colour_n beside_o it_o superinduce_v a_o haziness_n and_o dimness_n upon_o the_o figure_n so_o that_o it_o do_v not_o appear_v sharp_a and_o distinct_a the_o same_o inconvenience_n be_v also_o produce_v by_o monsieur_n hugenius_n way_n of_o cover_v the_o glass_n with_o the_o soot_n of_o a_o lamp_n though_o not_o to_o so_o great_a a_o degree_n the_o figure_n on_o paper_n or_o a_o smooth_a white_a surface_n be_v not_o magnify_v enough_o nor_o the_o difference_n of_o shadow_n so_o very_o distinct_a though_o that_o do_v very_o well_o if_o the_o surface_n be_v very_o smooth_a and_o the_o object_n be_v magnify_v by_o a_o hand_n glass_n that_o by_o the_o contract_a aperture_n be_v the_o worst_a of_o all_o by_o reason_n of_o a_o certain_a propriety_n of_o light_n not_o take_v notice_n of_o yet_o by_o optic_a writer_n the_o edge_n of_o object_n seem_v ragged_a of_o which_o i_o have_v hint_v somewhat_o in_o my_o animadversion_n pag._n 35_o and_o shall_v short_o say_v much_o more_o the_o whole_a ground_n of_o optic_n depend_v thereon_o the_o way_n of_o expand_v the_o figure_n of_o the_o sun_n by_o the_o eye_n glass_n
to_o i_o seem_v the_o best_a of_o all_o the_o rest_n but_o that_o be_v apt_a to_o vitiate_v the_o figure_n to_o super-induce_a somewhat_o of_o colour_n and_o do_v not_o give_v the_o small_a distinction_n of_o light_n and_o shadow_n without_o somewhat_o of_o colour_n and_o somewhat_o of_o haziness_n and_o dimness_n the_o glass_n of_o this_o helioscope_n may_v be_v make_v either_o by_o refract_v or_o reflect_v spherical_a glass_n the_o best_a way_n for_o take_v in_o a_o large_a angle_n be_v the_o use_v refracting_a glass_n both_o for_o the_o object_n and_o eye_n glass_n but_o the_o best_a way_n for_o take_v in_o a_o small_a part_n and_o for_o avoid_v haziness_n dimness_n and_o colour_n be_v by_o reflection_n either_o in_o part_n or_o in_o whole_a that_o be_v either_o to_o make_v the_o object_n glass_n only_o by_o way_n of_o reflection_n and_o the_o eye_n glass_n by_o that_o of_o refraction_n or_o both_o the_o object-glass_n and_o eye_n glass_n also_o by_o reflection_n and_o to_o have_v no_o refraction_n at_o all_o the_o several_a way_n of_o do_v which_o i_o have_v represent_v in_o the_o adjoin_a table_n wherein_o i_o have_v express_v ten_o several_a way_n of_o place_v the_o several_a glass_n so_o as_o to_o be_v fit_a for_o the_o use_v design_v the_o first_o way_n represent_v in_o the_o first_o figure_n be_v a_o sixty_o foot_n object-glass_n contract_v into_o a_o twelve_o foot_n tube_n by_o the_o help_n of_o four_o several_a reflecting-plate_n place_v between_o the_o object-glass_n and_o eye-glass_n the_o experiment_n of_o do_v which_o i_o produce_v and_o show_v before_o the_o royal_a society_n at_o divers_a of_o their_o public_a meeting_n at_o arundel_n house_n in_o the_o year_n 1668_o and_o it_o remain_v upon_o their_o register_n this_o as_o i_o then_o show_v will_v be_v of_o exceed_v great_a use_n in_o all_o manner_n of_o perspective_n and_o telescope_n if_o we_o can_v find_v a_o good_a material_a that_o will_v make_v the_o reflection_n very_o strong_a and_o full_a and_o that_o will_v not_o be_v subject_a to_o lose_v its_o figure_n which_o all_o our_o specular_a metal_n be_v very_o apt_a to_o do_v for_o by_o it_o it_o will_v be_v possible_a to_o contract_v the_o tube_n for_o long_a glass_n into_o very_o short_a length_n and_o so_o make_v they_o of_o easy_a use_n and_o manage_v this_o i_o attempt_v with_o several_a sort_n of_o metal_n make_v with_o ♃_o ♀_o ♂_o antimony_n and_o arsenic_n but_o most_o of_o these_o compound_a metal_n i_o find_v to_o be_v very_o spungy_a and_o consequent_o in_o the_o last_o polish_v to_o receive_v though_o a_o very_a glare_a polish_v yet_o such_o as_o do_v much_o confound_v the_o object_n by_o a_o kind_n of_o haziness_n especial_o if_o putty_n be_v use_v to_o glase_v it_o and_z for_o this_o purpose_n putty_n must_v not_o in_o any_o wise_a that_o i_o yet_o know_v of_o be_v use_v it_o be_v so_o very_o apt_a to_o round_o off_o the_o edge_n of_o pore_n or_o scratch_n which_o do_v much_o contribute_v to_o the_o haziness_n and_o confusion_n of_o the_o object_n if_o i_o make_v use_v of_o glass_n foil_v with_o quicksilver_n which_o i_o find_v to_o give_v much_o the_o best_a reflection_n yet_o i_o find_v this_o inconvenience_n that_o a_o considerable_a part_n of_o the_o ray_n be_v lose_v by_o the_o double_a reflection_n at_o the_o unfoil_v superficies_n of_o the_o glass_n the_o first_o from_o the_o surface_n of_o the_o glass_n before_o it_o enter_v this_o as_o it_o weaken_v the_o ray_n so_o mingle_v with_o the_o other_o reflection_n that_o come_v from_o the_o bottom_n it_o create_v some_o kind_n of_o haziness_n and_o confusion_n if_o the_o two_o superficies_n of_o the_o glass_n be_v parallel_n but_o if_o they_o be_v not_o parallel_v it_o superinduce_v somewhat_o of_o colour_n unless_o it_o be_v help_v by_o a_o contrary_a refraction_n in_o a_o second_o reflecting-glass_n after_o the_o manner_n of_o that_o which_o be_v delineate_v in_o the_o five_o figure_n where_o let_v a_o b_o represent_v the_o object-glass_n c_o g_o the_o first_o reflecting-plate_n who_o thin_a side_n be_v to_o c_o and_o d_o θ_o the_o second_a reflecting-plate_n who_o thin_a part_n be_v towards_o θ_o which_o do_v thereby_o take_v off_o the_o first_o refraction_n of_o c_o g_o and_o destroy_v the_o colour_n superinduce_v by_o the_o first_o the_o ray_n also_o be_v weaken_v much_o more_o from_o the_o second_o reflection_n it_o suffer_v at_o the_o unfoil_v superficies_n of_o the_o glass_n from_o the_o reflection_n of_o the_o air_n or_o aether_n which_o be_v much_o strong_a than_o that_o of_o glass_n at_o its_o re-enter_v into_o the_o air._n beside_o this_o i_o find_v that_o the_o substance_n of_o most_o glass_n be_v so_o imperfect_o mix_v that_o there_o be_v in_o the_o very_o best_o much_o of_o veinyness_n and_o inequality_n of_o refraction_n in_o the_o part_n thereof_o and_o thence_o though_o there_o be_v no_o visible_a vein_n appear_v in_o the_o body_n of_o the_o glass_n and_o though_o both_o the_o surface_v 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the_o glass_n and_o where_o our_o main_a aim_n and_o design_n be_v the_o loss_n of_o the_o strength_n and_o brightness_n of_o the_o ray_n and_o not_o for_o preserve_v the_o strength_n and_o briskness_n of_o the_o ray_n or_o augment_v they_o and_o therefore_o for_o this_o use_n the_o best_a material_a i_o have_v yet_o meet_v with_o be_v black_a glass_n black_a marble_n and_o glass_n of_o antimony_n for_o these_o substance_n be_v very_o dark_a and_o opaque_v do_v reflect_v but_o a_o very_a small_a part_n of_o the_o ray_n that_o fall_v upon_o it_o and_o none_o of_o those_o that_o penetrate_v into_o it_o especial_o if_o they_o be_v thick_a and_o be_v of_o a_o very_a hard_a and_o permanent_a substance_n be_v capable_a of_o receive_v a_o very_a curious_a and_o exact_a polish_v and_o qualify_v sufficient_o to_o retain_v and_o keep_v it_o without_o receive_v injury_n from_o the_o air_n or_o ordinary_a wipe_v but_o in_o the_o make_n of_o these_o glass_n for_o long_a telescope_n very_o great_a care_n and_o diligence_n must_v be_v use_v to_o make_v they_o of_o a_o true_a flat_a and_o so_o much_o the_o more_o by_o how_o much_o the_o near_o they_o be_v place_v to_o the_o object-glass_n and_o the_o further_a from_o the_o eye-glass_n a_o little_a err_v our_o at_o a_o great_a distance_n from_o the_o eye_n be_v vast_o magnify_v to_o the_o eye_n at_o that_o distance_n whereas_o a_o great_a become_v insensible_a if_o it_o be_v near_o the_o eye_n let_v a_o b_o in_o the_o first_o represent_v a_o sixty_o foot_n glass_n who_o focus_n be_v at_o o_o let_v a_o c_o d_o e_o f_o o_o and_o b_o g_o h_o i_o k_o o_o represent_v the_o two_o side_n ray_n of_o the_o pencil_n of_o light_n this_o pencil_n by_o the_o four_o reflect_v surface_n γ_n η_n δ_n θ_o ε_n ι_n ζ_n κ_n be_v break_v into_o five_o short_a length_n η_n δ_n answer_v to_o c_o d_o γ_n θ_o to_o g_o h_o δ_n ε_n to_o d_o e_o θ_o ι_n to_o h_z i_z ε_n ζ_n to_o e_o f_o and_o ι_n κ_n to_o i_o k_n and_o last_o ζ_n ο_n and_o κ_n ο_n to_o f_z o_o and_o k_o o_o as_o will_v be_v sufficient_o plain_a to_o any_o one_o that_o will_v but_o consider_v the_o scheme_n by_o this_o way_n four_o fifth_n of_o the_o length_n of_o the_o tube_n be_v take_v away_o which_o be_v the_o most_o that_o can_v be_v take_v away_o by_o four_o reflection_n every_o reflection_n run_v the_o whole_a length_n of_o the_o tube_n a_o lesser_a part_n of_o the_o length_n may_v be_v take_v away_o in_o any_o proportion_n assign_v as_o in_o the_o second_o contrivance_n describe_v in_o the_o second_o figure_n two_o three_o be_v take_v off_o when_o the_o same_o letter_n answer_v to_o the_o object-glass_n eye-glass_n the_o flexure_n of_o the_o side_n ray_n of_o the_o pencil_n and_o the_o