THE TRANSIT OF VENUS.

New Zealand Times, Volume XXIX, Issue 4282, 10 December 1874, Page 2

THE TRANSIT OF VENUS.

The long-looked-for 9th of December is over and gone, with all the hopes and fears that have been for the two last days entertained by our astronomers. Monday aud Tuesday were all—as we remarked yesterday—that could be desired by gardeners ; soft warm rain falling gladdened their hearts and proportionately dulled those whose souls were above the thoughts of “ a market-gardener.” On Tuesday night a south-east wind came up, with rain, but at the first of day-break there was every promise of a clear day. Up to ten o'clock all looked well, but then a fatal northwest air sprang up ; the clouds began to drift southward, and the usual results followed. The observers found an utter absence of all sharp definition ; the edge of the Sun quivered in the unsettled atmosphere ; and all exjiectations of any good observation vanished utterly. There was only the feeling left, as a miserable consolation, that all who had undertaken to observe the transit had done their best.

There are three different plans for utilising a transit of Venus. Halley’s, Deslilc’s, and by photography. In Halley’s plan observers both in the North and South Hemisphere would note the exact time in which Venus crossed the Sun; and as, from long obsevation, it is known perfectly how long Venus would take to cross the Sun at a centre path, the observers can place upon a drawing of the Sun the exact position of their transit lines. There will be a distance between these lines proportioned to the distance between the observing stations—roughly 21 times greater. Thus, knowing the distance between the lines, the value of the Sim's diameter is gained ; and, because the Sun appears so small, its distance from the Earth; as clearly a body so largo must he very far away to appear no larger than a sixpence. By Dcslile’s plan observers would see Venus entering upon the Sun at different times, the largest interval being about half an hour. As tire distance between the observers would Iso known exactly; and as the relative distances between the Earth and Venus, and Venus and the Sun, are known exactly, it is easy to calculate how far Venus has travelled in this time; and as the exact time in which Venus travels around the Sun is known perfectly from long observation, the length of this orbit can be calculated, the distance of Venus from the Sun, and, according to Kepler's third law, the distance of the earth from the Sun and of all the planets. The third method is by photography. An image of the sun can be taken as any ordinary picture is. The difficulty to be guarded against is any possible alteration of the coliodium film in the necessary photographic processes of fixing the picture. To ascertain the value of this alteration, line squares are ruled with mathematical accuracy on glass ; this glass, so prepared, is placed in the focus of the telescope, and so when a picture of the Sun, with Venus upon it, is taken, these lines are seen covering the plate with squares. If than the film altera irregularly the squares will be altered ; and as the exact size of the squares is known beforehand the necessary correction can bo applied, both for the altered squares and for Venus. Thus the result will bo as well known as if the film had not changed in any way. A plan has been invented by Jaansen, the Erench astronomer, by which the exact ci'itical moments, the junction of the Sun’s edge, as Venus enters, and the breaking up of the edge, as Venus leaves the Sun, will be gained, perhaps better than by any observation made by the eye. A circular photographic plate is fixed in a frame which can bo attached to tho telescope. Over this glass is a plate which rotates. The plate is perforated at its edge with small holes ; tho plate carries the glass with it ; each hole passes behind a small slit through which the sunlight will reach the plate. The exact time when each plate will be, in succession, under tho slit, is known. As this gear will bo set at work when the critical time is approaching, it is expected that the required phase will he found on some one of the plates.

There was yet another 'plan suggested by Father Secchi. The Sun’s edge, where Venus will enter, .would be observed by the spectroscope. As Venus approaches, the Sun’s spectrum -will alter, and from this alteration it is hoped that observations of the critical times would be gained perfectly. Some ask, what does it matter whether the Sun is at 95,000,000 miles, or at 92,000,000, which is about the true distance ? Such worthies may be safely left to answer their own question. Such was the position of affairs at Wellington at 1 o’clock yesterday; but the Sun brightened and showed Venus as a notch on the Sun; then as a half-circle, and then nearly as a circle; but just at the moment when all attention was fixed for the ingress contact, a cloud covered the Sun. At mid-transit, Venus was seen by many and very plainly by the naked eye. The Wellington observers were Dr. Hector, Mr. Parsons, Mr. Buchanan, and Archdeacon Stock. Mr. Deveril has secured a permanent record of the transit in an excellent photograph. The return from Major Palmer, at Burnham, ivas as unsatisfactory as that from Wellington. But there are so many stations in the South Hemisphere, that at some of these a good result may have been obtained, and the Sun’s distance secured therefore by comparison with observations in the Northern Hemisphere We are gratified in being able to state that at a late hour last night, Mr. Lemon, the general manager of the Telegraph department, received the following very satisfactory telegram from Mr. Palck, telegraphist, Queenstown, province of Otago : “ Pleased to inform you that Professor Peters [the American Astronomer] was very successful in taking observations of the transit of Venus here.” The following telegrams came to hand through the Press Agency, in the course of the evening : Nelson, 1.45 p.m. The sky has been overcast all morning, but the Sun is now breaking out. 3.36 p.m. The transit was distinctly seen from the first contact up to 2.45 p.m., when the sky again became clouded over. 7 p.m. The sky cleared again at 4.30 p.m., and from that time the progress of Venus across the Sun was distinctly visible until the last contact. Greyjiouth, Wednesday, 2.44 p.m. Weather very unfavorable for observations. Occasional breaks in the clouds enabled the passage of Venus across the Sun to be seen, but nothing like the continuous progress of the transit could be followed. Hokitika, Wednesday, 1.4 p.m. There is a beautiful blue sky. The clouds have nearly cleared off. It is expected that a good view of the transit will be obtained, and every available appliance is in use for that purpose. 2.15 p.m. There was a clear sky at the commencement of the transit. Up to this time two satisfactory observations have been taken. Christchurch, 1.28 p.m. The sky continued to clear up from the morning, and the sun shone brightly, but a heavy mass of clouds has come up from the south-west, aud completely obscured the Sun. The sky appears lighter in the direction of the Burnham Observatory; but, altogether, circumstances are very unfavorable to the observation, and do not appear likely to improve. 2 p.m. The sky is almost clear, Venus is distinctly visible just inside the Sun’s disc. 4.5 p.m. The Sun shone brightly for about an hour, but heavy clouds again came up and obscured it completely. There is now scarcely any hope of further observations. Lyttelton, 6 p.m. The weather here has been most unfortunate, the sky having been completely overcast all day, excepting from 2.15 to 4 p.m. Tisiabu, 3.53 p.m. The weather cleared at two o’clock. The transit of Venus was then seen. The internal contact, however, was completed when the phenomenon was first seen. Port Chalmers, 5.7 p.m. The weather to-day has been very bad, with heavy showers. Dunedin, 6 p.m. Every preparation had been made for observing the transit, at Rockyside (Caversham) and at Roslyn, but no observation could be obtained. The Sun is now shining strongly. The egress of Venus was plainly visible. Balclutha. The weather here was cloudy, with an overcast sky. No opportunity was afforded for observing transit. Queenstown. The weather here cleared as if specially for the observation, from noon to three o’clock, when rain clouds again obscured the sky. Hopes are yet held out of final observations being taken. 4.58 p.m. Further observations are being taken, with every hope of success, now. Nasery. The weather was cloudy, with rain, but cleared up for ten minutes about three minutes .after the first contact. About two-thirds of the diameter of Venus was on the Suu, when the observations were again interrupted by heavy showers from the south. The weather at 4.40 p.m. is so cloudy that it is hardly possible an observation of egress can be taken. Clyde. This was a most unfavorable day—cloudy, with occasional showers. The Suu was only visible at intervals between one aud three o’clock. The Bluff. A dark spot was seen at intervals during the day crossing the Suu. New Plymouth. The weather is clearing up, aud the transit is likely to be visible here. Grahamstown, 5 p.m. It is raining heavily. There is no chance of an observation. The Sun was visible at a quarter to one o’clock, for the only time to-day. Tauranca, 2.5. p.m. The weather is so cloudy that there is no chance of observations being made hero, Auckland, 2.30 p.m. At the time of the commencement of the transit the sky was completely overcast, and not a glimpse of the Sun could be obtained. 4 p.m. The sky continued heavily overcast all day. Captaiu Heale, specially appointed to conduct the observation hero, failed to got a view. Lambert’s party, consisting of himself aud Messrs. Pond aud Martin, were observing from Hobsou-street. They succeeded in getting a view of the first contact, which was noticed at Ih, 00m. 37secs., Greenwich time (subject to corrections). The formation of the black drop was noticed at lb. 58m. At 2h. 17m. lOsccs. another glimpse of the Suu was caught, and the planet was fully on. Subsequently the sky became so overcast that further observation was impossible. 0 p.m. Noue of the Auckland observers saw anything of the final phase of the transit. MAJOR PALMER’S REPORT. Christchurch, 10 p.m. Major Palmer reports as follows from Burnham Observatory ;—Hero the observation of ingress was spoiled by clouds, which prevented any measures with the double image micrometer from being made prior to internal contact, and entirely hid the planet from view a few seconds before the contact itself. Photogtaphs near contact were impossible. About fourteen minutes after contact, the Sun showed a little more brightly. At intervals a few micrometrical measures of the distances of limbs were made during some eight or ten minutes; but these would ho of little value. A few photographs, moat of them indifferent, were also secured. At 3 o’clock the Sun became entirely hidden. Heavy rain set in at

3.30, and lasted till 4.30, when a little clearing, and the look of the sky to windward gave hopes that the observations of egress (of immensely greater value than that of ingress) might yet be secured, but clouds again gained the mastery, and the Sun was not seen at all from half-past three until some ten minutes after the end of the transit, when it shone brightly till nearly sunset. The five sub-stations, at Grahamstowu, Auckland, Wellington, Dunedin, and Naseby, met with the same bad fortune as we did, both at ingress and egress. The telegraphic arrangements by Mr. 0. Lemon and his staff were excellent. The weather only failed us.