Some Late Curious Astronomical Observations Communicated by the Reverend and Learned Mr. James Pound, Rector of Wansted, and R. Soc. Soc.

IV. Some late curious Astronomical Observations communicated by the Reverend and Learned Mr. James Pound, Rector of Wansted, and R. Soc. Soc. The Occultation of Jupiter by the Moon observed at Wansted the 14th of July in the Morning, 1715. Having after Midnight carefully corrected the Clock by no less than ten Observations of the Altitude of the Lucida Arietis, the Error thereof was found $5' 13''$ too fast, the extremes not differing above $6''$: And in the morning about $7^h$, by as many Altitudes of the Sun, with a like Agreement, the same Error was found $5' 14''$, to be deducted from the Times shewn by the Clock. | Julii 13°. P. M. N. | Time by the Clock | Time correct | |-------------------|------------------|-------------| | The Third Satellite of Jupiter was hid by the Moon | 13 27 33 | 13 22 20 | | The first Satellite was hid | 13 32 35 | 13 27 22 | | The Second Satellite was hid | 13 34 25 | 13 29 11 | | The first Contact of the Limbs of $\alpha$ and $\epsilon$ Jupiter wholly hid | 13 34 54 | 13 29 41 | | The Third Satellite came out from behind the dark side of the Moon | 13 36 23 | 13 31 10 | | The first Satellite | 14 7 25 | 14 2 12 | | The Second Satellite | 14 12 25 | 14 7 12 | | The first Limb of Jupiter came out | 14 14 38 | 14 9 25 | | The following Limb of Jupiter, or last Contact | 14 14 45 | 14 9 32 | | The fourth Satellite emerged | 14 16 15 | 14 11 2 | R r r Jupiter Jupiter and the Satellites were to the Northward of the visible Way of the Moon's Center. This Occultation was observed through a Telescope, in which the Focal Length of the Object Glass was $14\frac{1}{2}$ Feet, and of the Eye Glass $2\frac{3}{4}$ Inches. And the Aperture of the Object Glass was $1\frac{1}{2}$ Inch. I could perceive no Colours on Jupiter's Limb, either at his immersion or Emerfion, when the Axis of the Tube was directed to him. | Apparent Time | An Eclipse of the Moon observed at Wansted October 30, 1715 | |---------------|----------------------------------------------------------| | h. | | | 15 09 00 | The Eclipse had been for some time begun | | 17 00 | The Moons Diameter measured by a Micrometer was | | 22 25 | The Chord connecting the Horns | | 35 45 | The inlightned Part of the Diameter continued to the Chord between the Horns | | 43 24 | The inlightned Part of the Diameter | | 49 50 | The same repeated | | 52 43 | The same repeated | | 56 51 | The inlightned part of the Diameter continued to the Chord between the Horns | | 59 27 | The inlightned Part of the Diameter | | 16 04 04 | The same repeated | | 18 34 | The same again repeated | | 23 45 | The Chord between the Horns | | 26 30 | The same repeated | 14 | h. | The same again | |----|----------------| | 14 | At which time also the Shade passed thro' the middle of Schikardus. | | 15 | The Chord between the Horns, agreeing with the D's Diameter | | 16 | The inlightned part of the Diameter | | 17 | The same produced to the Chord between the Horns | | 18 | The same repeated | | 19 | The inlightned part of the Diameter | | 20 | The same | | 21 | The Edge of the Shadow passed thro' the Middle of Gaffendus. | | 22 | The inlightned part produced to the Chord between the Horns | | 23 | The Chord between the Horns | | 24 | The same repeated | | 25 | The same again | | 26 | The same again | | 27 | The same again | | 28 | The same again | | 29 | The same again | | 30 | The same again | | 31 | The same again | | 32 | The same again | | 33 | The same again | | 34 | The same again | | 35 | The same again | | 36 | The same again | | 37 | The same again | | 38 | The same again | | 39 | The same again | | 40 | The same again | | 41 | The same again repeated | R r 2 At 17h. 39' the Eclipse was thought to be ended; and was visibly so at 17h. 41': But by comparing the last Observations of the Chords between the Horns, it follows that the true End of the Eclipse was at 17h. 38'. 20''. At 17h. 43' the Moon's Diameter was 33'. 40''. The Middle cannot be supposed to be very accurately determined by these Observations, which were not sufficiently distant from the time of the greatest Obscuration. However by comparing several of them together, the Middle will be obtained, viz. | By Obs. 3. compared with Obs. 24. at | 16 15 21 | |-------------------------------------|-----------| | By Obs. 4. compared with Obs. 22. at | 16 15 58 | | By Obs. 5. compared with 19. and 20 at | 16 16 00 | | By Obs. 6. and 7. compared with 16. at | 16 15 48 | By reason of Clouds I could not see the Beginning of the Eclipse, nor make such Observations of the Moon's immersing into the Shadow as I did of her emerging out of it. By Observation 11. compared with Observation 15. the Digits Eclipsed were 8'. The Angles were measured by a Micrometer in a 15 Foot Telescope. I have not considered how far they are consistent with one another; they being set down here exactly as they were first taken. This Eclipse is the more considerable, as happening very near the Moon's Perigee, and therefore useful to verify her Anomaly; as also to limit the greatest Diameter of the Shadow of the Earth, and consequently the Parallax of the Moon. This may very properly be compared with that of the 19th of October, 1697, whose middle was at 7h. 41'. P. M. at London, and Quantity the same as now. The Times by the Clock were $17\text{h}.45\text{m}$. sooner than the apparent time, as was found by the following Observations of Cor Leonis and Arcturus, which through the Clouds were but just discernible. | Apparent Zenith Distance | Time by the Clock | Apparent Time by Calculat. | The Difference | |--------------------------|-------------------|----------------------------|---------------| | of Cor | h. | h. | Mean Diff. | | 70°16' | 13 32 43 | 13 50 35 | 17 52 | | 69°38' | 36 50 | 54 44 | 17 54 | | 69°09' | 40 06 | 57 51 | 17 45 | | 68°40' | 43 09 | 14 00 59 | 17 50 | | 68°08' | 46 3 | 04 26 | 17 59 | of Arctur. | 65°19' | 17 37 40 | 17 55 24 | 17 44 | | 65°06' | 39 12 | 56 48 | 17 36 | | 64°41' | 41 49 | 59 29 | 17 40 | | 63°47' | 47 40 | 18 05 17 | 17 37 | Clock too slow 17 45 The Latitude of Wansted is $51°.34'$. Its Longitude is $8''$ in time Eastward from the Observatory at Greenwich. The Account given of this Eclipse by the Reverend Mr. William Derham, who observ'd it at Upminster, is agreeable to this, as far as Clouds would permit him to observe.