THE TRANSIT OF VENUS IN 1769 AS OBSERVED IN SCOTLAND.

Wanganui Chronicle, Volume XXIV, Issue 9662, 7 November 1882, Page 3

THE TRANSIT OF VENUS IN 1769 AS OBSERVED IN SCOTLAND.

(By Alexander Brown, L.L.D. Arbroath.) The closing month of the- present year will be memorable astronomically on account of the transit of the planet Venus across the disc of the sun on the afternoon of (in New Zealand, the morning of Thursday, 6th) Wednesday, 6th December, 1882. ■' This transit will be visible in Scotland for more than an hour and a half if the sky in the south western horizon happens at the time to be unclouded. As the last time that a transit of Venus was visible in Scotland was on the afternoon of Saturday, 3rd June, 1769 (that is fully 133 ye»rs ago), it may be interesting to advert to some of the circumstances attending the observation of that rare phenomenon on that occasion. The day was one of alternate . shower: and- sunshine,' the sky in some places covered with ex tremely- dense clouds,, in ■ others thunder 'apd lightning occurred. At most places the clouds cleared away shortly before sunset, and the sun was seen as he de ■ scended unclouded below the northwestern horizon. As it will be on the ocasion of the transit to which we are looking forward, the transit of 1769 was visible in Scotland for about an hour and a half, the sun at setting being seen with theplanet projected upon his face. The localities where observations of the phenomenon were made and recorded, and which have come down to us, are the following, namely, Hawkhill, near Edinburgh; Kirknewton Manse, southwest of Edinburgh, and Glasgow Observatory. Hawkhill is situated north of Lochend Loch, about a mile to the north-east of . where . the Eoyal Observatory now stands, and at that time was the residence of Lord Alemoor, one of the Lords of Session, who was remarkably fond of the science of astronomy, and had a small, observatory fitted up at his residence. The observers at this station were Mr James Hoy, who observed in a room on the ground floo.r of the house with a 3J feet achromatic telescope; Lord Alenioorobserved on the floor above with an 18-inch reflector, and James Lind, M.D.,'observed in the observatory with a two feet achromatic telescope. . Every one. of these observers noticed the black ligament now termed the black drop, at the time of internal contact of the, limbs of the sun and .planet. The physical cause of , this phenomenon is doubtless analogous to the similar phenomenon sometimes seen during total and annular solar eclipses, and has occasioned much discussion and remains unexplained. Mr Hoy held the position of land steward to Lord Alemoor. In September, 1776, he left Hawkhill, and five years afterwards became private secretary to the Duke of Gordon, at Gordon Castle, where he resided till his death in 1827. He was a man of singular honesty and uprightness of character, and a great student; he cultivated the sciences of astronomy, botany, natural history, chemistry, and meteorology. He carried on an extensive correspondence with scientific and liberary men—among the latter was the poet Burns. Dr. Lind was the inventor of that form of anemometer for measruing the pressure of. wind which is called ,by his. name. Kirknewton is 17 miles'west-of Hawkhill, .as ascertained by measuring the distance on 1 Lawrie's map of the environs of Edinburgh. The observer of the transit there was the minister of the parish, the Rev. Alexander Bryce, who was crdained to thi charge in 1745, and died in 1786, aged 73 years. He was a very good astronomer, and a writer in the " Philosophical Transactions." Mr A. Bryee observed that when the' suu, with Venus on ' his disc, was near the horizon, her border-appeared full ,of notches and protuberances, and she seemed as if moving round like a wheel. The Glasgow observing party was arranged and superintended by the celebrated Dr. Alexander Wilson, the Professor of Practical Astronomy in the University, and besides ,Dr. Wilson, consisted of Professors Eeid, Williamson, and Irvine, and Mr Patrick Wilson, Dr. Wilson's .son, and successor in the Astronomical Chair. -In consequence of the unfavourable state of the atmosphere there was a remarkable undulation in the sun's limb, and a considerable tremour round Venus, when she was observed on the sun's disc, and as a result it was impossible to measure her diameter. After the centre of Venus had passed the sun's limb she appeared of an oblong fipure, the longest diameter passing through the centre of the sun. At the time of internal contact Venus apparently adhered to the sun's limb by a dark protuberance or neck, the length and breadth of which varied every instant by a constant undulation. This neck did not break suddenly, but changed colour from black to a dark brown till at last the interval between Venus and the sun's limb appeared quite clear. Tho observations taken in 1769 at all the stations, both northern and southern, have been ascertained by different methods of calculation to have been erroneous, owing, in all probability, to the fact that the first apparent entrance of Venus upon the sun cannot be exactly observed; it is only tho moment when she is fully on his disc and about to pass from his outer border or the moment of interior contact that can be observed, and at that moment it curious elongation of the figure of the planet occurs, which misled the observers who were not then prepared for is. ' It is also necessary, in order to have trustworthy observations, that the sun should not be too near the horizon; for, if he is, \ 1 ; <■ ) : : >

atmospheric influences will render them wholly uncertain.