Page images

at which time he sketched out Venus's situation upon paper, which Horrox found to coincide with his own observations.

Mr. Horrox, in bis treatise on this subject, published by Hevelius, and from which almost the whole of this account has been collected, hopes for pardon from the astronomical world, for not making his intelligence more public; but his discovery was made too late. He is desirous, however, in the spirit of a true philosopher, that other astronomers were happy enough to observe it, who might either confirm or correct his observations. But such confidence was reposed in the tables at that time, that it does not appear that this transit of Venus was observ. ed by any besides our two ingenious countrymen, who prosecuted their astronomical studies with such eagerness and precision, that they must very soon have brought their favourite science to a degree of perfection unknown at those times. But unfortunate. ly Mr. Horrox died on the 3d of January 1640-1, about the age of 25, just after he had put the last hand to his treatise, intitled Venus in Sole visa, in which he shews himself to have had a more accurate knowledge of the dimensions of the solar system than his learned commentator Hevelius.So far the Annual Register.

In the year 1691*, Dr. Halley gave in a paper upon the transit of Venus (See Lowthorpe's Abridgment of Philosophical Transactions, page 434.), in which he observes, from the tables then in use, that Venus returns to a conjunction with the Sun in her ascending node in a period of 18 years, wanting 2 days 10 hours 524 minutes; but that in the second conjunction she will have got 24' 41" farther to the south than in the preceding. That after a period of 235 years 2 hours 10 minutes 9 seconds, she returns to a conjunction more to the north by 11' 33" ; and after 243 years, wanting 43 minutes in a point more

See the Connoissance des Temps, for A. D. 1761.

to the south by 13' 8". But if the second conjunction be in the year next after leap-year, it will be a day later.

The intervals of the conjunctions at the descend. ing node are somewhat different. The second happens in a period of 8 years, wanting 2 days 6 hours 55 minutes, Venus being got more to the north by 19' 58". After 235 years 2 days 8 hours 18 mi. nutes, she is 9' 21" more southerly : only, if the first year be a bissextile, a day must be added. And after 243 years 0 days 1 hour 23 minutes, the con. junction happens 10' 37" more to the north ; and a day later, when the first year was bissextile. It is supposed as in the old style, that all the centurial years are bissextiles.

Hence, Dr. Halley finds the years in which a transit may happen at the ascending node, in the month of November (old style) to be these-918, 1161, 1396, 1631, 1639, 1874, 2109, 2117: and the transit in the month of May (old style) at the descending node, to be in these years—1048, 1283, 1518, 1526, 1761, 1769, 1996, 2004.

In the first case, Dr. HALLEY makes the visible inclination of Venus's orbit to be 9° 5', and her ho. rary motion on the Sun 4' 7". In the latter, he finds her visible inclination to be 8' 28", and her horary motion 4' 0". In either case, the greatest possible duration of a transit is 7 hours 56 minutes.

Dr. Halley could even then conclude, that if the interval in time between the two interior contacts of Venus with the Sun could be measured to the exactness of a second, in two places properly situate, the Sun's parallax might be determined within its 500dth part.-But several years after, he explained this affair more fully, in a paper concerning the transit of Venus in the year 1761; which was published in the Philosophical Transactions, and of which the third of the preceding articles is a translation; the original having been written in Latin by the Doctor.


Containing a short account of some observations of

the transit of Venus, A. D. 1761, June 6th, new style ; and the distances of the planets from the Sun, as deduced from those observations.

Early in the morning, whe'i every astronomer was prepared for observing the transit, it unluckily happened, that both at London and the Royal Observatory at Greenwich, the sky was so overcast with clouds, as to render it doubtful whether any part of the transit should be seen :--and it was 38 minutes 21 seconds past 7 o'clock (apparent time) at Greenwich, when the Rev. Mr. Bliss, our Astronomer Royal, first saw Venus on the Sun; at which instant, the centre of Venus preceded the Sun's centre by 6' 18".9 of right ascension, and was south of the Sun's cen. tre by 11' 42".1 of declination.-From that time to the beginning of egress, the Doctor made several ob. servations, both of the difference of right ascension and declination of the centres of the Sun and Ve. nus; and at last found the beginning of egress, or instant of the internal contact of Venus with the Sun's limb, to be at 8 hours 19 minutes 0 seconds apparent time. From the Doctor's own observations, and those which were made at Shirburn by another gentleman, he has computed, that the mean time at Greenwich of the ecliptical conjunction of the Sun and Venus was at 51 minutes 20 seconds after five o'clock in the morning; that the place of the Sun and Venus was 0 (Gemini) 15° 36' 33"; and that the geocentric latitude of Venus was 9' 44".9 south.-Her horary motion from the Sun 3' 57". 13 retrograde ;--and the angle then formed by the axis of the equator, and the axis of the ecliptic, was 6° 9' 34", decreasing hourly 1 minute of a degree. By the mean of three good observations, the dia. meter of Venus on the Sun was 58".

Mr. Short made his observation at Savile-House in London, 30 seconds in time west from Greenwich, in presence of his Royal Highness the Duke of York, accompanied by their Royal Highnesses Prince Wil. liam, Prince Henry, and Prince Frederick.He first saw Venus on the Sun through flying clouds, at 46 minutes 37 seconds after 5 o'clock; and at 6 hours 15 minutes 12 seconds he measured the diameter of Venus 59''.8.-He afterward found it to be 58".9 when the sky was more favourable.—And, through a reflecting telescope of two feet focus, magnifying 140 times, he found the internal contact of Venus with the Sun's limb to be at 8 hours 18 minutes 214 seconds, apparent time; which, being reduced to the apparent time at Greenwich, was 8 hours 18 minutes 51} seconds : so that his time of seeing the contact was 84 seconds sooner (in absolute time) than the instant of its being seen at Greenwich.

Messrs. Ellicott and Doland observed the internal contact at Hackney, and their time of seeing it, reduced to the time at Greenwich, was at 8 hours 18 minutes 36 seconds, which was 4 seconds sooner in absolute time than the contact was seen at Greenwich.

Mr. Canton, in Spittle-Square, London, 4' 11" west-of Greenwich (equal to 16 seconds 44 thirds of time), measured the Sun's diameter 31' 33" 24"", and the diameter of Venus on the Sun 58"; and by observation found the apparent time of the internal contact of Venus with the Sun's limb to be at 8 hours 18 minutes 41 seconds; which, by reduction, was only 2 seconds short of the time at the Royal Observatory at Greenwich.

The Reverend Mr. Richard Haydon, at Leskeard, in Cornwall (16 minutes 10 seconds in time west from London, as stated by Dr. Bevis) observed the internal contact to be at 8 hours 0 minutes 20 se. conds, which by reduction was 8 hours 16 minutes

30 seconds at Greenwich: so that he must have seen it 2 minutes 30 seconds sooner in absolute time than it was seen at Greenwich-a difference by much too great to be occasioned by the difference of parallaxes. But by a memorandum of Mr. Haydon's some years before, it appears that he then supposed his west 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 answer.

At Stockholm observatory, latitude 59° 20' north, and longitude 1 hour 12 minutes east from Greenwich, the whole of the transit was visible; the total ingress was observed by Mr. Wargentin to be at 3 hours 39 minutes 23 seconds in the morning, and the beginning of egress at 9 hours 30 minutes 8 seconds; so that the whole duration between the two internal contacts, as seen at that place, was 5 hours 50 minutes 45 seconds.

At Torneo in Lapland (1 hour 27 minutes 28 seconds east of Paris) Mr. Hellant, who is esteemed a very good observer, found the total ingress to be at 4 hours 3 minutes 59 seconds; and the beginning of egress to be 9 hours 54 minutes 8 seconds.-So that the whole duration between the two internal contacts was 5 hours 50 minutes 9 seconds.

At Hernosand in Sweden (latitude 60° 38' north, and longitude 1 hour 2 minutes 12 seconds east of Paris), Mr. Gister observed the total ingress to be at 3 hours 38 minutes 26 seconds; and the beginning of egress to be at 9 hours 29 minutes 21 seconds.-The duration between these two internal contacts 5 hours 50 minutes 56 seconds.

Mr. De La Lande, at Paris, observed the begin. ning of egress to be at 8 hours 28 minutes 26 seconds apparent time—But Mr. Ferner (who was then at Constans, 14.1" west of the Royal Observatory at Paris) observed the beginning of egress to be at 8 hours 28 minutes 29 seconds true time,

« PreviousContinue »