Observations of the Eclipses of Jupiter's Satellites, from 1700, to the Year 1727. By the Reverend W. Derham, M A Canon of Windsor and F. R. S. Communicated by Sr. Hans Sloane, Bart. President of the College of Physicians and Royal Society, &c.

I. Observations of the Eclipses of Jupiter's Satellites, from 1700, to the Year 1727. By the Reverend W. Derham, M.A. Canon of Windsor and F.R.S. Communicated by Sr. Hans Sloane, Bart. President of the College of Physicians and Royal Society, &c. ### Eclipses Primi Satellitis. | Dies Mensis | Tempus æquale | Tempus apparen. | Per Tab. Flamst. & Cassini. | Qualis Eclipse | Locus Jovis Helioc. | |-------------|---------------|-----------------|----------------------------|---------------|---------------------| | | | | | | Grad. | | | H. M. S. | H. M. S. | Min. Sec. | | | | Aug. 13 | 10. 59. 4 | Anno Domini 1700 | 10. 57. 10 | Em. | ≈ 15 Telescopio 6. pedali. | | Dec. 1 | — — — | | 5. 1. 8 | E. | ≈ 10 Telesc. 16. pedali. | | | | | 4h. 55'½ C. | | | | | | | 1. 38 4. 58 Fl. | | | | | | | | | | | Jun. 15 | 13. 23. 0 | Anno Domini 1701 | 13. 21 Fl. | Im. | ≈ 27 | | Jul. 8 | 13. 30. 0 | | 13. 28 Fl. | I. | ≈ 29 | | Oët. 12 | 5. 54. 9 | | 5. 59 C. | E. | ✷ 8 Bona Observatio. | | | 54. 19 | | | | | | | 54. 49 | | | | | | | 7. 48. 57 | | 7. 55 C. | E. | ✷ 9 Bona. | | | 49. 47 | | | | | | Dec. 20 | 6. 25. 0 | | 6. 28 Fl. | E. | ✷ 14 Dubia. | | | | | | | | | Oët. 15 | 9. 22. 0 | Anno Domini 1702 | 9. 23 Fl. | E. | ρ 11½ Optima. | | | 22. 15 | | 9. 26 C. | | | | | 22. 45 | | | | | | | 5. 44. 57 | | 5. 47 Fl. | E. | ρ 12 Optima. | | | 45. 21 | | 5. 50 C. | | | | | 45. 42 | | | | | | Dec. 9 | 5. 59. 0 | | 6. 5 Fl. | E. | ρ 16½ Aer nebulosus. | K k k Dies | Dies Mensis | Tempus æquale | Tempus apparente | Per Tab. Flamst. & Cassini | Eclipse qualis | Locus Jovis | Grad. | |-------------|---------------|-----------------|--------------------------|---------------|------------|-------| | Aug. 8 | | | | | | | | Aug. 24 | | | | | | | | Sep. 2 | | | | | | | | Nov. 28 | | | | | | | Anno Domini 1703 | H. M. S. | H. M. S. | H. Min. | Grad. | |----------|----------|---------|-------| | 15. 21. 30 | 15. 18 F. | I. | χ 8½ Dubia ob Nebulas. | | 13. 43. 6 | 13. 38 F. | I. | χ 10 Bona. | | 13. 45 C. | | I. | χ 11 Nebulosum Cælum. | | 10. 8. 20 | 10. 4 F. | I. | χ 19 Non mala. | | 5. 37. 40 | 5. 44. 52 | E. | χ 19 Non mala. | Anno Domini 1704 | H. M. S. | H. M. S. | H. Min. | Grad. | |----------|----------|---------|-------| | 17. 7. 43 | 17. 9. 53 | 17. 8 F. | I. | χ 12 Nimia lux, sed non mala. | | 11. 38. 18 | II. 37 F. | I. | χ 13 Bona. | | 13. 33. 5 | 13. 23 F. | I. | χ 13½ Bona. | | 10. 16. 40 | 10. 13 F. | I. | χ 16 Nebulosa, sed non mala. | | 17. 10 | | I. | χ 18 Nebulosum. | | 9. 14. 43 | 9. 9. 17 | E. | χ 21 Dubia. | | 9. 14. 43 | 9. 9. 17 | E. | χ 23 Bona. | Anno Domini 1705 | H. M. S. | H. M. S. | H. Min. | Grad. | |----------|----------|---------|-------| | 9. 46. 3 | 9. 47 F. | E. | χ 29 Bona. | | 46. 40 | | | | | 47. 0 | | | | | 10. 9. 58 | 10. 7. 18 | 10. 10 F. | E. | χ 30½ Bona. | | 10. 11. 5 | 8. 25 | | | | 16. 39. 15 | 16. 45. 26 | 16. 52 F. | I. | χ 35 Bona. | | 40. 15 | 46. 26 | | | | 18. 54. 50 | 19. 10. 19 | 19. 10 C. | I. | χ 39 Nimia lux, ideo dubia. | | 55. 20 | 10. 49 | | | | 19. 4. 50 | 19. 13. 59 | | I. | χ 21 | | 19. 15. 0 | 19. 13. 20 | 19. 11 F. | I. | χ 22 Dominus Gray hanc immersionem Cantuariae 19h. 15' observavit. | Anno Domini 1706 | H. M. S. | H. M. S. | H. Min. | Grad. | |----------|----------|---------|-------| | 7. 27. 0 | 7. 26 F. | E. | χ 29½ Emersum inveni. | | 7. 46. 40 | 7. 45. 25 | 7. 48 F. | E. | χ 3 Bona. | | 47. 37 | 46. 20 | | | | 9. 59. 2 | 10. 3. 5 | 10. 3 F. | E. | χ 3½ Nebulosum. | Dies ### Eclipse Primae Satellitis | Dies Mensis | Tempus aquale | Tempus apparen. | Per Tab. Flamsteed & Cassini | Qualis Eclipse | Locus Jovis | |-------------|---------------|----------------|-------------------------------|---------------|------------| | | H. M. S. | H. M. S. | H. Min. | Grad. | | | Feb. 15 | 10. 17. 52 | 10. 4. 43 | 10. 3 F. | E. | 26 1/2 | | —— 24 | 6. 39. 52 | 6. 28. 20 | 6. 28 F. | E. | 27 1/2 Bona. | | Mar. 26 | 8. 47. 53 | 8. 45. 36 | 8. 46 F. | E. | 29 1/2 Ventus fortis tubum motitavit. | | Maii II | 9. 14. 43 | 9. 18. 43 | 9. 20 F. | E. | 3 1/2 Bona. | | Jan. 31 | | 17. 35. | | I. | 23 1/2 Immersus fuit ante. | **Anno Domini 1707** | Maii 18 | 9. 7. 26 | 9. 10. 47 | 9. 18 F. | E. | Non mala. | | Jun. 10 | 9. 22. 21 | 9. 21. | 9. 27 F. | E. | 3 1/2 Bona. | **Anno Domini 1709** | Maii 14 | 10. 6. 57 | 10. 10. 26 | 10. 14 F. | E. | 26 | | Jul. 15 | | 8. 46. | 8. 49 F. | E. | 2 Immerfum vidi. | | Aug. 23 | 7. 22. 2 | 7. 22. 50 | 7. 28 C. | E. | 5 Non mala. | **Anno Domini 1710** | Aug. 19 | | 8. 23. 40 | 8. 32 F. | E. | 4 Bona. | | | | 24. 30 | 8. 30 C. | | | **Anno Domini 1711** | Oct. 27 | 8. 10. 28 | 8. 26. 19 | 8. 35 F. | E. | 14 Bona. | | Dec. 28 | 7. 4. 18 | 6. 56. 30 | 7. 5 F. | E. | 19 1/2 Bona. | **Anno Domini 1713** | Oct. 23 | 9. 59. | 10. 1. 1 | 10. 5 F. | E. | 17 Dubia. | | Nov. 1 | | 6. 20. | 6. 28 F. | E. | 18 Nubilum ideo dubia licet tubo 34 pedali observationem feci. | K k k 2 Dice ### Eclipsis Secundi Satellitis. | Dies Mensis | Tempus æquale | Tempus apparente | Per Tab. Flamst. & Cassini | Qualis Eclipse | Locus Jovis | |-------------|---------------|-----------------|---------------------------|---------------|------------| | | H. M. S. | H. M. S. | H. M. | Grad. | | | Feb. 1 | 6. 25. 3 | 6. 10. 15 | 6. 14 F. | E. | 1 Bona. | | | 26. 18 | 11. 30 | 12. 00 | | | | | 26. 48 | 8. 7. | 8. 9 F. | E. | 1 1/2 Bona.| | | 21. 21 | 7. 30 | 8. 12 C. | | | | | 21. 51 | 8. | | | | | | 22. 21 | | | | | **Anno Domini 1717.** Per Tabul. D. Bradley. Sequentes Observatio- nes Telescopio 12 1/2 pe- dali optimo factæ fuere. Windedoriae, dubia. | Nov. 27 | 9. 8. 36 | 9. 6. B. | | | | |-------------|---------------|-----------------|-----------------------|---------------|------------| **Anno Domini 1726.** | Jan. 5 | 7. 40. 19 | 7. 29. 49 | 7. 31 B. | E. | 25 Bona, Upministro. | |-------------|---------------|-----------------|-----------------------|---------------|----------------------| | | 41. 0 | 30. | | | | | | 41. 30 | 31. | | | | | Aug. 5 | 14. 50. 17 | 14. 46. 28 | 14. 47 B. | I. | 15 Bona. | | | 51. 7 | 47. 18 | | | | | Sep. 15 | 7. 44. 17 | 7. 53. 10 | 7. 53 B. | I. | 19 Bona. | | | 45. 37 | 54. 30 | | | | | | 46. 7 | 55. | | | | | Oct. 8 | 10. 25. | 10. 7 B. | | E. | 21 Observatio incerta | | | | | | | | | | | | | | | Dec. 2 | 7. 2. | 7. 5 B. | | E. | 25 Windedoriae, dubia.| | | 3. | | | | | | | 7. 12. 57 | 7. 9 B. | | E. | 28 Upministro bona. | | | 13. 57 | 8. | | | | **Observationes Eclipsium Secundi Satellitis Jovis.** | Anno Domini 1700. | |-------------------| | Oct. 27 | | 8. 24. 0 | | 8. 23 | | E. | | 6 1/2 | Sequentes Observatio- nes Telescopio 16 peda- li factæ fuere. Dubia propter vapo- res. D. Flamsteedii Minister observavit cir- ca 8h. 16'. p.m. ### Eclipsis Secundi Satellitis | Dies Mensis | Tempus æquale | Tempus apparens | Calculatio Flamsteedii | Qualis Eclipse | Locus Jovis Helioc. | |-------------|---------------|-----------------|------------------------|---------------|---------------------| | | H. M. S. | H. M. S. | H. M. | Grad. | | | Jun. 29 | --- | --- | --- | --- | | | Jul. 31 | Inter | --- | --- | --- | | | Oct. 21 | --- | --- | --- | --- | | | Nov. 22 | --- | --- | --- | --- | | #### Anno Domini 1701 | | 10. 50. 0 | 10. 52 | I. | 28 1/2 Dubia ob vapores. | |---------------|-----------|-------|---|--------------------------| | | 9. 43. 0 | | I. | 1 Nubilofum. | | | 10. 3. 0 | | | | | | 7. 39. 35| | E.| 8 1/4 Bona. | | | 40. 0 | | | | | | 41. 0 | | | | | | 10. 18. 2| | E.| 9 Bona. | | | 20. 0 | | | | | | 7. 26. 18| | E.| 11 1/2 Bona. | | | 27. 0 | | | | #### Anno Domini 1702 | | 9. 46. 0 | 10. 17 | I. | Immersum inveni. | |---------------|---------|-------|---|--------------------------| | | 15. 0. 51| | I.| 8 Bona. | | | 1. 51 | | | | | | 7. 5. 21 | | E.| 11 1/2 Bona. | | | 6. 22 | | | | | | 7. 22 | | | | | | 9. 40. 38| | E.| 12 Bona. | | | 41. 0 | | | | | | 42. 13 | | | | #### Anno Domini 1703 | | 9. 50. 0 | 10. 11 | I. | 9 3/4 Immersum inveni. | |---------------|---------|-------|---|--------------------------| | | 15. 3. 0| | I.| 24 Immersus ante. | | | 8. 41. 9| | E.| 20 1/2 Bona. | | | 8. 38. 7| | | | | | 9. 6 | | | | #### Anno Domini 1704 | | 12. 15. 29| 12. 32 | I.| II 12 Bona. | |---------------|-----------|-------|---|--------------------------| | | 17. 10. 44| 17. 32| I.| II 16 Bona. | | | 11. 14 | | | | | | 9. 2. 19 | | I.| II 10 Haud mala. | | | 9. 26 | | | | | Dies Mensis | Tempus æquale | Tempus apparen. | Calculatio Flamsteedii | Qualis Eclipse | Locus Jovis Helioc. | |-------------|---------------|-----------------|------------------------|---------------|---------------------| | | H. M. S | H. M. S | H. M. | | Grad. | | Anno Domini 1705 | | | | | | | Jan. 15 | — — — | 7. 47. 0 | 8. 14 | E. | II 24. 3 Emerso ante. | | — 20 | 10. 30. 23 | 10. 16. 9 | 10. 50 | E. | II 25. 3 Bona. | | Feb. 14 | 7. 45. 31 | 7. 32. 0 | 8. 1 | E. | II 27. 3 Vaporosus aer: dub. | | Mar. 25 | 10. 15. 10 | 10. 12. 30 | 10. 36 | E. | § 0 Incerta propter vicinitatem primi Sat. | | Apr. 26 | — 16. 5 | 13. 25 | 10. 29 | E. | § 3. 3 Vaporosus Horizon: dub. | | Sep. 29 | 16. 26. 11 | 16. 39. 11 | 16. 48 | I. | § 16. 3 Bona. | | Oct. 31 | 15. 55. 20 | 16. 10. 52 | 16. 27 | I. | § 19 Bona. | | Dec. 20 | 9. 49. 30 | 9. 45. 36 | 10. 11 | I. | § 23 Bona. | | Anno Domini 1706 | | | | | | | Apr. 20 | — — — | 8. 58. 30 | 9. 31 | E. | § 3 Fuerat emersus. | | Anno Domini 1707 | | | | | | | Mar. 13 | — — — | 7. 59. 0 | 8. 18 | E. | § 28. 3 Emersit ante. | | — 20 | 10. 28. 14 | 10. 23. 54 | 11. 5 | E. | § 29 Dubia. | | Apr. 14 | 7. 33. 17 | 7. 35. 39 | 8. 9 | E. | IX 0. ½ Dub. propter nim. lucem. | | — 21 | 10. 9. 33 | 10. 12. 51 | 10. 45 | E. | IX 1. ¾ Bona. | | Anno Domini 1710 | | | | | | | Mar. 4 | — — — | 17. 5. 0 | — — — | I. | IX 21. ¾ Nubilum, & incerta. | | Anno Domini 1711 | | | | | | | Jul. 15 | — — — | 9. 16. 0 | 9. 6 | E. | VS 1. ½ Nebulosum & dub. | | Anno Domini 1712 | | | | | | | Oct. 12 | 7. 35. 6 | 7. 50. 30 | | E. | W 10 Bona. | | Anno Domini 1714 | | | | | | | Nov. 1 | — — — | 6. 34. 7 | 6. 55 | E. | V. 18 Incerta ob nubes. | | Dec. 3 | — — — | 6. 14. 26 | 6. 34 | E. | V. 21 Bona. | | Anno Domini 1716 | | | | | | | Dec. 22 | — — — | 4. 55. 0 | — — — | E. | II 27. 4 Emerso ante fuit. | Dies ### Eclipses Tertii Satellitis. | Dies Mensis | Tempus æquale | Tempus apparens | Calculatio Flamst. & Molyn. | Qualis Eclipse | Locus Jovis Helioc. | |-------------|---------------|----------------|----------------------------|----------------|---------------------| | | H. M. S | H. M. S | H. M | Grad. | | | Jan. 30 | | | Anno Domini 1717 | | Emersum inveni. | | | | | 7. 24. 0 | 7. 46 | E. | | Oct. 30 | | | Anno Domini 1725 | | Bona observatio Tele- | | | | 9. 16. 23 | | scopio 12 ½ pesdali opt. | | | | | 17. 0 | 8. 46 M. | E. | | | | | 17. 18 | | | | Aug. 28 | | | Anno Domini 1726 | | Bona. | | | | | 8. 52. 25 | 8. 54. 52 | I. | | | | | 53. 55 | 56. 22 | | | Oct. 17 | | | | 8. 58 M. | | | Nov. 25 | | | | 5. 53 M. | E. | | | | | | 8. 27. 15 | | | | | | | 8. 16 | E. | | | | | | | | ### Observationes Eclipsium Tertii Satellitis Jovis. | Oct. 19 | | | Anno Domini 1700 | | | | | | | 6. 23. 15 | 6. 13 | I. | | | | | | | ≈ 6 | | Jul. 11 | | | Anno Domini 1701 | | | | | | | 10. 18. 0 | 10. 11 | I: | | | | | | | | | Sep. 28 | | | | 10. 25. 27 | E. | | | | | | 10. 12 | | | | | | | 26. 0 | | | | | | | 26. 42 | | | Jul. 26 | | | Anno Domini 1702 | | | | Aug. 2 | Inter | | | 10. 51. 13 | E. | | | | | | 10. 33 | | | | | | | 11. 55. 0 | I. | | | | | | 11. 35 | | | | | | | | | Dubia. Bona. Nubes interrumpebant. ### Eclipses Tertii Satellitis | Dies Mensis | Tempus æquale | Tempus apparense | Calculatio Flamsteedii | Qualis Eclipse | Locus Jovis Helioc. | |-------------|---------------|------------------|------------------------|---------------|---------------------| | | H. M. S | H. M. S | H. M. | | Grad. | | Jul. 12 | — — — | 14. 46. 0 | 15. 32 | I. | 8 6 Fuit Immersus. Optima observatio Immersionis: at somno invadente, nimis sero Emerzionem vidi. | | Aug. 24 | — — — | 13. 43. 20 | 13. 4 | I. | 8 10 | | Sep. 22 | — — — | 16. 6. 36 | 15. 40 | E. | 8 12 4 | | Sep. 29 | — — — | 9. 57. 44 | 9. 17 | I. | 8 13 | | Oct. 6 | 13. 46. 13 | 14. 0. 30 | 13. 19 | I. | 8 14 Bona. | In Observationibus Aug. 24, Sep. 22, 29, & Oct. 6. notandum est, Latitudinem tertii Satellitis majorem fuisse quam C. Flamsteedius, aut Cassinus conjectarunt. Nam iste Satelles usque ad extremum Poli Jovis marginem evagatus est, & (antequam in ejus umbram propter immersus est) diu in ejus penumbra latuit: & in eadem umbra non ultra duas horas permanisse autumo, quamvis post Observationes Aug. 24, & Sep. 29, moram diurniorem fuisse videatur. Sed in priore observatione, veram non vidi Emerzionem: & in posteriore cum * & ‡ fuerit) Emerzion Jovis limbo tam propinqua fuit, ut difficile fuerit eam cum Telecopio 16 pedali vere observare. | Anno Domini 1704 | |------------------| | Sep. 14 Inter | | 16. 58. 0 | E. II 14 1/2 Nubilum cælum. | | 17. 10. 0 | 16. 32 | | 10. 28. 40 | I. II 17 Bona. | | Oct. 20 10. 14. 34 | 9. 48 | | Nov. 3 18. 12. 16 | 18. 27. 17 17. 45 | | Nov. 3 18. 12. 16 | I. II 18 1/4 Bona, licet aer nebulos. | | Anno Domini 1705 | |------------------| | Jan. 14 | | 10. 7. 5 | 9. 53. 57 I. II 24 1/2 Bona. | | 9. 4 | 55. 56 | | Feb. 26 | | 10. 9. 32 | 9. 58. 7 I. II 28 1/2 Bona. | | 58. 42 | | | Oct. 6 Inter | | 17. 18. 0 | E. 35 17 | | 27. 0 | | | Nov. 25 | | 7. 41. 0 | I. 25 21 Incerta per Nebulas densas. | ### Eclipses Tertii Satellitis | Dies Mensis | Tempus æquale | Tempus apparens | Calculatio Flamsteedii | Qualis Eclipse | Locus Jovis Helioc. | |-------------|---------------|----------------|------------------------|---------------|---------------------| | | H. M. S. | H. M. S. | H. M. | | Grad. | | Mar. 13 | — — — | 8. 52. 27 | 7. 36 | E. | Bona. | | — 20 | — — — | 9. 24. 0 | 9. 3 | I. | Dubia ob ¼ vicinitatem. | | Nov. 4 | — — — | 16. 59. 27 | 16. 50 | I. | Non mala. | | Maii 17 | — — — | 8. 17. 0 | — — | E. | Emersum inveni. | | Nov. 26 | 18. 41. 37 | 18. 49. 15 | 18. 41 | E. | | | Dec. 3 | 19. 19. 38 | 19. 24. 1 | 19. 25 | I. | Bona. | | Feb. 5 | 17. 35. 32 | 17. 21. 0 | 17. 26 | I. | | | — 37. 4 | — 22. 32 | | | | | | Jul. 14 | — — — | 9. 45. 0 | 9. 41 | E. | Dubia. | | Sep. 16 | — — — | 6. 15. 0 | 6. 28 | I. | Dubia ob nimiam lucem. | | — 20. 0 | — 52. 0 | 10. 5 | | E. | Bona. | | Okt. 29 | — — — | 6. 26. 30 | 6. 45 | I. | Bona. | | Dec. 26 | 6. 38. 30 | 6. 32. 0 | 6. 46 | E. | Ventus dubiam reddidit. | | Sep. 17 | 8. 26. 56 | 8. 36. 9 | 8. 40 | I. | Bona, Tubo 34 pedali. | | — 28. 56 | — 38. 9 | | | | | | Okt. 23 | 7. 22. 0 | 7. 24. 0 | 7. 38 | E. | Bona, Tubo 16 pedali. | | — 25. 0 | — 27. 0 | | | | | | Dec. 5 | — — — | — — — | 7. 37 | E. | Hic Satelles magnam habet Latitudinem, & nisi fallor, nullam pafla est Eclipse hæc nocte. | LII ### Eclipses Tertii Satellitis. | Dies Mensis | Tempus æqualis | Tempus apparenis | Calculatio Flamsteedii | Qualis Eclipse | Locus Jovis Helioc. | |-------------|----------------|------------------|-----------------------|---------------|---------------------| | | H. M. S. | H. M. S. | H. M. | | Grad. | | Jan. 17 | | | | | | | Anno Domini 1717 | 5. 52. 23 | 8. 48. 38 | I. E. | Bona. Mala. | | Jan. 5 | | | | | | | Anno Domini 1726 | 6. 41. 10 | 6. 30. 40 | E. | Bona, Telescop. pedali. | | Dec. 15 | | | | | | ### Observationes Eclipsiuum Quartii Satellitis. | Anno Domini 1701 | Jun. 11 | Sep. 3 | |------------------|---------|--------| | | 14. 20. 0 | 14. 35 | | | 13. 59. 0 | 14. 21 | | I. | 27 | Immersum inveni. | | E. | 4 | Idem per nebulas. | | Anno Domini 1704 | Sep. 30 | Dec. 6 | |------------------|---------|--------| | | 9. 21. 42 | 9. 40 | | | 9. 52. 44 | | | E. | 15 | Nebulosum, ideo dubia. | | E. | 21 | Dubia ob proximitatem Jovis, & parvitetem Satel. | | Anno Domini 1705 | Feb. 11 | |------------------|---------| | | 8. 38. 5 | 8. 24. 8 | 8. 23 | | I. | 27 | Non mala. | | Anno Domini 1706 | Mar. 20 | Sep. 20 | |------------------|---------|---------| | | 9. 3. 2 | 8. 58. 40 | 9. 36 | | | 16. 24. 0 | 16. 17 | | I. | 0 | Non mala. | | I. | 15 | Immersum inveni. | | Anno Domini 1712 | Aug. 20 | |------------------|---------| | Inter. | 8. 29. 0 | 10. 11 | | 39. 0 | 7. 43. 0 | 44. 0 | | 45. 0 | 9. 20 | E. | 7 | Bona. | Remarks on the foregoing Tables. As exact Tables to calculate the Eclipses of the Circumjovials, would be of very great Service to find the Longitude of Places; so I have some Hopes that these Observations of some of them, in more Revolutions than one of Jupiter in his Orb, may be of Use to correct, or make such Tables. I wish that I could have made them more compleat (and in my younger, and more leisurely Days, I endeavoured to do it, by rising at unseasonable Hours, &c.) but besides cloudy and bad Weather, one great Hindrance was the Want of Tables, to enable me to calculate the Eclipses myself, and the frequent Disappointments of my Friends, that furnished me with Catalogues of them. And moreover, many times Company, and Business, and (to tell the Truth) sometimes Forgetfulness, have hindered the Constancy of my Observations: But the greatest Chasms in them were caused by some dangerous Fits of Sickness, which so impaired me, that I have not dared, ever since, to venture upon Observations at unseasonable Hours of the Night. As to my Manner of observing, it was (for the most Part) with a 16 Foot Telescope, and afterwards with an excellent one (not inferior to it) of 12½ Feet, that, at Jupiter's Light, bears an Aperture of 2½ Inches, and a Charge of about 2 Inches. And as to the Time; I made use of an excellent and well-adjusted Clock, corrected at Noon, by the Meridional dional Transits of the Sun, observed with the Instrument described in the Philos. Transact. No 291, which shews the Noon-time to one or two Seconds. This Way some of my skilful Friends (particularly Mr. Flamsteed) suspected to be fallacious, and not comparable to taking the Time by Altitudes of the Sun, or fix'd Stars. For a Trial therefore, I gave him a Challenge, of observing some Eclipse that we agreed on; which when we compared, we found so nicely to agree, as to shew to a Second of Time, or very nearly so, the Difference of the Meridian of the Observatory, and that of Westminster. But because the Credit of my Observations depends upon the Strictness of the Time, give me Leave to compare my Instrument with a Quadrant. And here I will presume to affirm, that my Instrument is no more liable to Errors than a Quadrant. 1. It is less so, in regard of its Structure: For a little Error in the Division of a Quadrant's Limb, or in fixing its Sights (whether Telescopick or Plain) spoils all. But no great Curiosity, or Niceness is required in my Meridian-Instrument. 2. In point of Observation, as much Care and Exactness is necessary to guard against Wind, and to take a true Altitude by the Quadrant, as is necessary to take a true Azimuth by my Instrument. For if we are sure that the Instrument is exactly in the Meridian (the Manner of which is shewn in the fore-cited Transaction) we can be as sure, and that to as few Moments of Time, as any the best Quadrant can shew it. And although I cannot say, that every Day, or every Week, I examined the Position of my Instrument, yet I did it so often, as to be satisfied, that not many, or great Errors, could be in my Observations. The greatest Part of the Eclipses, that were the most accurately made, may easily be distinguished by the two, or more Numbers of the Time of Observation: The first of which shews the Moment of the Beginning of the Eclipse; the following, the Times when farther advanced: As in an Emersion, the first Number shews the Time, when the Satellite appears like a small obscure Spot; the following Numbers, when brighter, or quite emerged out of Jupiter's Shadow; and so contrariwise in an Immersion. But altho' this might have sufficed, yet for greater Certainty and Satisfaction, I have noted which Observations were good, which doubtful, or bad: Even the latter of which may be of Use in some Cases, where better are wanting. The calculated Times of the Eclipses I have inserted, where I had them from others, or could calculate them myself, as being of good Use to amend the Tables of Mr. Flamsteed, Cassini, or others, taken Notice of in the Column on Purpose. And for the same Reason I thought good to add the Place of Jupiter also. And lastly, I thought it good to mention the Length and Power of the Telescope I used; as being, in some Measure, necessary in the comparing Observations of different Places; because Observations may differ several Seconds, by the different Length and Goodness of the Telescope used; a long and good Telescope shewing the Satellite, when the Shadow of Jupiter doth but just touch it: Whereas a short, or bad one, doth not shew it, until one half, or more, of the Satellite is enlightened. Which Difference is most remarkable in the Eclipses of the two outermost Satellites, in their greatest Latitudes; at which Times they go into, and come out of Jupiter's Shadow, in an oblique and longer, not a direct and shorter Path: An Instance of which may be seen in the Observations of the Eclipses of the Third Satellite in the Months of August and September, 1703. II. A Description of a Roman Pavement found near Grantham in Lincolnshire, with the Oecconomy of the Roman Times in this Part of England, communicated in a Letter to Dr. Rutty, R. S. Secr. by W. Stukeley, M. D. Col. Med. Lond. &c R. S. Soc. SIR, LAST Week I had an Occasion of examining a curious Piece of Roman Antiquity discovered near us, and resolv'd to send you the following Account of it, together with a Drawing I made of it. In Feb. 1727-8. Plowing in the open Fields of Denton, about 2 ½ Miles from Grantham, they happen'd upon a Roman Pavement in Mosaic Work, as commonly call'd. I had Notice of it from my Neighbour, the Rev. Mr. Saul, Minister of Harlaxton, the next Parish, and went to see it. It lies partly in the glebe Land, partly in Madam Welby's, who assisted us with Workmen to clear it. It has been a very large Room about 30 Foot both ways, as we found by digging in divers Places; but being so near the Surface, not above a Foot, or a Foot and half deep, and having been plow'd