TRANSIT OF VULCAN.

New Zealand Times, Volume XXXII, Issue 4990, 21 March 1877, Page 3

TRANSIT OF VULCAN.

Every preparation has been made' by Dr. Hector, Archdeacon Stock, and other gentlemen who take a deep 'interest in scientific matters, for a careful observation of the disc of the sun during to-day arid the remainder of the week. In.fact one or two have been watching the sun at every opportunity during the past few; days." Some particulars as to the reason of the observations being made and the results expected to b« derived from them may be interesting just now. According to. Mr. H. C. Russell, the Government Astronomer of New South Wales, who has been writing to the papers on the subject, the great French Astronomer, M. Leverrier, by what he haa written about the possibility of a small planet being found within the orbit of Mercury, during the last few months, has drawn a good deal of attention to the subject. It was he who first seriously suggested such a planet as the cause of certain small irregularities in the motion *f. Mercury, and his previous labors in the Solar system, especially the share he had in predicting that Neptune would be found in an. indicated position in the heavens,, has given great weight to the statement he now makes, namely, that there may be a transit of -Vulcan on the 22nd March (to-morrow). A round black spot has frequently bean seen in transit over the sun's disc, but always under unfavorable conditions, and out of the 30 instances he has collected, M. . Leverrier selects two, that of Stark and Steinheibel, on February 12, .1820, and that of Lescarhault, qn 26th March, 1859, and from these computes a period of 280'077 days, but he has variously estimated the period from other observations at from 25-6 days to 42 days. On the 4th April, 1876, M. Weber, a practised observer at Pe-chee-lee, saw a round black Bpot in transit over the sun. When this news reached the great French astronomer he again took up his subject, and announced to European and American astronomers by -telegram that there might be a transit in October, 1876. A careful watch was kept during October, bui it ended in disappointment, except in one case. Mr. W. G. Wiight,' of California, Bays that he saw such a spot in transit on the 23rd of October ; but, excepting those who saw through the same telescope, no one confirms Mr. Wright's statement. In his recent investigation M. Leverrier : points out that both Venus and Mercury, make two transits within 10 years, and then not another for a century ; and that probably Vulcan will obey the same law, and from the imperfect observations to hand it would appear that the planet makes its two transits 'in seven years and a half, and that there may- be;one on. 22nd March, 1877, after which there .cannot be another until 1883. Up .to the .time of_. writing, nothing has been seen of the planet from Wellington .observatories; and after all the small chance there is of ■ its being detected will be appreciated when it is known that the diameter of Vulcan is estimated at 6secs., and that it will appear as a small spot' on the sun, only 100th part of the size. Venus presented when in transit in 1874, Venus as it was observed through the instruments in Wellington which are now in use appearing as of the size of ,a marble only. The time occupied in! transit j will be about two hours. It will how-' ever bo » perfectly black spot,--without any, penumbra, and may be readily distinguished from a gun spot by its motion. ,• M. Leverrier thinks the transit will be almost tangentical,! or.only over a small part of the sun's disc. It 1 may be .added that at present a dim spot it; visible, and so. large is it that it may almost l be discovered by the aid of smoked glass.. If; a transit of Vulcan be observed, photographs I of the sun's disc will at.once be.taken, all preparations to that end having been made. I