The Transit of Venus.

Cromwell Argus, Volume V, Issue 269, 24 November 1874, Page 7

The Transit of Venus.

Every boy in the public schools who is moderately well advanced in astronomy has a tolerably clear idea of the solar system. It is represented to him with the sun as a centre, around which seven or eight planets are whirling in circles, of which there is one to each planet, and that these circles are distant from the sun in varipus degrees—that of Mercury, or perhaps the problematic Vulcan, being the nearest, and Neptune the farthest. But the fact is that the planets move in ellipses rather than circles, and that the elongation of the paths upon which they travel will, at certain stated times, cause them to move directly across a portion of the sun’s orb. Such a movement is called the transit of a planet. For the purpose of observation from the earth, the transit of Venus is the only one that is of any practical use. In the eighteenth century a French astronomer, M. Delambre, discovered a star very close to the sun, which he has set down as a planet, and given the name of Vulcan, but its existence is doubtful. Next to it in nearness comes Mercury, but it. revolves so close to the central body that ft is very rarely seen with the naked eye in our latitude. There have been attempts to take observations of its transit, but they have resulted in failure. Next comes Venus, and then the Earth, the other planets being still farther distant from the sun than that which we inhabit. Of their transit of course we know nothing, because they do not cross the disc of the sun within our range of observation. But, for astronomical calculations, the transit of Venus is the great event to students upon our. world. These transits have acquired immense interest and importance from the fact that they supply data by which the sun’s distance from the earth can be determined with far greater precision than by any other known method. Venus revolves in an orbit within tha •, of the Earth, and, next to the sun and moon, is the most brilliant object in the firmament visible to us. In the last century astronomers perceived the importance of observing her transit across the sun, and when it took place, in 1759, there were fifty-nine stations established in the localities where the phenomenon was visible, nearly all the in Europe sending out expeditions to take •observations. The atmospheric conditions were highly favourable, and excellent views were obtained ; but the defects of the instruments then in use and the faultiness of the calculations led to a wide "difference in the estimates of the distance •of the earth from the sun. The magnitude of Venus is nearly equal to that of the Earth, and its intense lustre dazzles the eye and aggravates the optical defects ■of the instruments used. These difficulties interfered greatly with the observations made in 1769 ; but there was another and greater obstacle not apprehended before the expeditions started out. This was at the precise moment of the movement of the planet across the sun—whether it should be taken when the outer edges ■of each hinged upon the other, or when the line of departure could be precisely perceived. One expedition made calculations on the one basis and and another on the other, so when they were reckoned up the distance between the earth and the sun was figured up at all the way from 87,890,870 miles to 108,984,560 miles. Such diverse figures were of but little use to students, and about the year 1822 the famous German astronomer, Encke, took hold of them, and after working them up fixed the proper distance at 95,274,000 miles. This was held to be correct standard until, in 1854, Hanson overhauled the calculations and presented 91,659,000 of miles as the result. Various other astronomers worked up the problem until it was fixed by general consent at 92,000,000 miles in round numbers, and if these figures are wrong the world looks to the observations to be made in next December to correct them. There is a cqrions coincidence in the fact, as evolved by Professor Smyth, that the distance now recorded is precisely that of the dimensional features of the great Pyramid, a demonstration that many of the illustrations now regarded as recent acquisitions of astronomical science were known to the architects of that most remarkable structure. The line of difference between ancient astrology and modern astronomy is indeed scarcely perceptible, and in studying the work done centuries ago we cannot but marvel at the results achieved by the scientists of the oldeu time, notwithstanding that they were so mixed with magic and mysticism. The minuteness of the work of the scholars who recasted the figures of the observations of 1769 may be estimated when it is stated as Sir J«ha Herschell says, that the

corrections correspond to the apparent breadth of a human hair one hundred and twenty-five feet distant or a sovereign eight miles away, And it is' such refinement of science upon which we now expect to improve. The transit of Venus, which takes place in December next, is the first since that of 1769. With the faults of previous obser vations as guides, and the perfection of instruments thathasbeen recently achieved, it is supposed that we shall now approach very nearly to absolute correctness. The transit will not be visible in those parts of the world where it could be most easily observed. It will be visible in various parts of the extreme northern hemisphere, but the most favourable station will be far away in the south.. -Mr Proctor, in his admirable work, says that for the observation of a transit which occurs in December the weather is most likely to be good in the southern hemisphere and bad in the northern. If the atmospheric conditions are equally favourable to each, the work would be greatly simplified. But as it is, the most important stations will be in the distant south, and it is to these points that the various governments are sending the majority of their expeditions. Russia alone confines the work of her scientists to the north, having established a chain of posts of observation across Siberia ; but other governments are looking in the other direction. The Polynesian Islands in the South Sea will be the most favourable stations, and to them the United States, Great Britain, France, and Germany are sending a great number of their details for observation. The Swatara, which sailed from New York, will land her first party at the Crozet Islands. Twenty-seven parties will be sent out by the Russian Government, seven by France, five by England, four by Germany, and three by the Government of New South Wales. The necessity of so many parties is obvious on account of the probability that cloudy weather will interfere with the observations at many points. The results to be determined include the distance of the earth from the sun, the distance of Venus from each, and the correction of the errors which were made in the observations of the transit of 1769, to which we have previously alluded. —Baltimore AmeriJune 23 rd.