Page:Encyclopædia Britannica, first edition - Volume I, A-B.pdf/522

 43 S ASTRO place on the fame day and hour next year, and will crofs the equator 90 degrees farther to the weft; which makes. the time of the equinox a quarter of a day (or about fix of our days) later every year. Hence^ although the fpiral in which the fun’s motion is performed, be of the fame fort every year, yet it will not be the very fame, becaufe the fun will not pafs vertically over the fame places till four annual revolutions are finiihed. Venus’s orbit is inclined 3^ degrees to the earth’s; and crolfes it in the 14th degree of Gemini and of Sagittarius ; and therefore, when the earth is about thefe points of the ecliptic at the time that Venus is in her inferior conjuration, (he will appear like a fpot on the fun, and afford a more certain method of finding the diftances of all the planets from the fun, than any other yet known. But thefe appearances happen very feldom. The firft was in the year 1639. The fecond in the year 1761, June 6. In the morning of that day, when the fun rofe at London, Venus had pafied both the external and internal contafts. At 38 minutes 21 feconds paft 7 o’clock, (apparent time) at Greenwich, the Rev. Dr Blifs, aftronomer royal, firft faw Venus on the fun; at which inftant, the centre of Venus preceded the fun’s centre, by 6/ iS^.9 of right afcenfion, and was fouth of the fun’s centre by iS7 of declination.—From that time to the beginning of egrefs, the Dotfor made feveral obfervations, both of the difference of right afcenfion and declination of the centres of the fun and Venus; and at laft found the beginning of egrefs, or-inftant of the internal contaCf of Venus with the fun’s limb, to be at 8 hours 19 minutes o feconds apparent time.—From the Doctor’s own obfervations, and thofe which were made at Shirburn by another gentleman, he has computed, that the mean time at Greenwich of the ecliptical conjunction of the fun and Venus was at 51 minutes 20 feconds after 5 o’clock in the morning; that the place of the fun and Venus was Gemini 150 36' 33w; that the geocentric latitude of Venus was or 44".9 fouth,—her horary motion from the fun 3' 5 7”. 13 retrograde, and the angle then formed by the axis of the equator and the axis of the ecliptic was 6° 9* 34", decreafing hourly 1 minute of a degree.—By the mean of three good /obfervations, the diameter of Venus on the fun was 58 Mr Short made his obfervations at Savile-houfe, in London, 30 feconds in time weft from Greenwich, in prefence of his royal highnefs the duke of York, accompanied by their royal highnefles prince William, prince Henry, and prince Frederick.—He firft faw Venus on the fun, through flying clouds, at 46 minutes 37 feconds after 5 o’clock; and at 6 hours 15 minutes 12 feconds he meafured the diameter of Venus 59".8.:—He afterward found it to be 5%".9, when the Iky was more favourable.—And, through a reflecting telefcope -of two feet focus, magnifying 140 times, he found the internal contaCt of Venus with the fun’s limb to be at 8 hours 18 minutes 2 It feconds, apparent time; which being reduced to the apparent time at Greenwich, was 8 hours 18 minutes 51^ feconds; fo that his time of feeing the contact was 8t feconds fooner (in abfolute time) than the inftant of its being feen at Greenwich. MdTrs Ellicott and Dollond obfexved the internal con-

N O M Y. taCt at Hackney; and their time of feeing it, reduced to the time at Greenwich, was at 8 hours 18 minutes 56 feconds, which was 4 feconds fooner in abfolute time than the coptaCt was feen at Greenwich. Mr Canton’ in Spittle-Square, London, 4' 11" weft of Greenwich, (equal to 16 feconds 44 /,/thirds of time), meafured the fun’s diameter 31' 33" 24, and the diameter of Venus on the fun 58^; and, by obfervation, found the apparent time of the internal contaCl of Venus with the! fun’s limb to be at 8 hours 18 minutes 41 feconds ; which, by reduction, was only 2-f feconds fliort of the time at the Royal Obfervatory at Greenwich. The Reverend Mr Richard Haydon, at Leflceard in Cornwall, (16 minutes 10 feconds in time weft from London, as ftated by Dr Bevis), obferved the internal contact to be at 8 hours o minutes 20 feconds, which, by reduction, was 8 hours 16 minutes 30 feconds at Greenwich; fo'that he muft have feen it 2 minutes 30 feconds fooner in abfolute time than it was feen at Greenwich ;—a difference by much too great to be occafioned by the difference of parallaxes. But by a memorandum of Mr Hayden’s fome years before, it appears that he then fuppofed his weft longitude to be near two minutes more; which brings his time to agree within half a minute of the time at Greenwich; to which the parallaxes will very nearly anfwer. At Stockholm Obfervatory, latitude 590 2o'4- north, and longitude 1 hour 12 minutes eaft from Greenwich, the whole of the tranfit was vifible: the totalingrefs was obferved by Mr Wargentin to be at 3 hours 39 minutes 23 feconds in the morning, and the beginning of egrefs at 9 hours 30 minutes 8 feconds ; fo that the whole duration between the two internal contacts, as feen at that place, was 5 hours 50 minutes 45 feconds. * At Torneo in Lapland, (1 hour 27 minutes 28 feconds eaft of Paris), Mr Hellant, who is efteemed a very good obferver, found the total iogrefs to be at 4 hours 3 minutes 59 feconds, and the beginning of egrefs to be 9 hours 54 minutes 8 feconds.^—So that the whole duration between the two internal contacts was 5 hours 50 minutes 9 feconds. At Hernofand in Sweden, (latitude 6° 38' north, and longitude 1 hour 2 minutes 12 feconds eaft of Paris), Mr Qifter obferved the total ingrefs to be at 3 hours 38 minutes 26 feconds; and the beginning of egrefs to be at 9 hours 29 minutes 21 feconds;—the duration between thefe two internal contacts 5 hours 50 minutes 56 feconds. Mr De La Lande, at Paris, obferved the beginning of egrefs to be at 8 hours 28 minutes 26 feeonds apparent time.—But Mr Ferner (who was then at Conflans, 14% weft of the Roy;1! Obfervatory at Paris) obferved the beginning of egrefs to be at 8 hours 28 minutes 29 feconds true time. The equation, or cjjfference between the true and apparent time, was 1 minute 54 feconds.— The total ingrefs, being before the fun rofe, could not be feen. At Tobol(k in Siberia, Mr Chappe obferved the total ingrefs to be at 7 hours o minutes 28 feconds in the morning, and the beginning of egrefs to be at 49 minutes 20t feconds after 12 at noon.—So that the whole duration of the tranfit between the internal contacts was hours5