« EelmineJätka »
and photospheric areas were deduced from the Kew observations of spots; and from a consideration of these data, and confining the question strictly to changes of terrestrial temperature due to this cause alone, Langley deduces the result that“sun-spots do exercise a direct effect on terrestrial temperature by decreasing the mean temperature of the earth at their maximum." This change is, however, very small, as “it is represented by a change in the mean temperature of our globe in eleven years not greater than 0.3° C., and not less than 0.05° C.”
Professor Langley has also had constructed an apparatus, which is similar in principle to one devised by Dr. Hastings. It consists of two prisms by which two spectra from various parts of the sun can be juxtaposed. Comparing the light from the two limbs, for example, one is enabled to discriminate the atmospheric lines, and the proof of solar rotation and a measure of its velocity is easily to be had. It has also other applications.
Nyrén, of Pulkova, has published an important paper on the position of the equinox for 1865.0, derived from observations of the sun made with the Pulkova transit instrument (Wagner) and vertical circle (Döllen and Gylden). The deduced position of the equinox differs by +0.064" from that assigned by Greenwich observations, by +0.055" from Pulkova (1845), by +0.011" from Paris, and -0.002" from Washington.
Professor Wolf, of Zurich, who has collected all available data in regard to sun-spots for nearly twenty-five years, has now these data for more than 22,000 days between 1749 and 1876. Since 1848 these data may be said to be complete. The mean value of the solar-spot period he finds to be 11.111 years + 0.307; but single periods may be two years longer or shorter than the mean. The maximum is nearer the preceding minimum than the following one. A longer period of about 178 years (not 55) is also indicated. It is to be noted that 16 sun-spot periods, 15 revolutions of Jupiter, 6 of Saturn, and 298 of Venus are nearly equal.
Sun-spots continue to be observed photographically at Greenwich, Paris, Moscow, Toulouse, Kasan, Vassar College, and are observed visually at Madrid, Oxford, Berlin, Zurich, Leipzig.
Protuberances are observed at Palermo, Rome, Greenwich, Moscow, O’Gyalla, etc.
The chief signal-officer of the army has proposed to the various observatories of this country, both public and private, to co-operate in physical observations of the sun. Every phenomenon of interest should be registered, whether relating to spots, faculæ, or protuberances, etc. Each observatory that is willing to take up any special field, or that already occupies such a field, is requested to give its results, or such part of them as it is willing to give, to the Signal Bureau for record in its Monthly Weather Revier. Thus a prompt publication is secured. In response to this invitation, the United States Naval Observatory is furnishing a record of the number of spots daily observed on the sun's disk. This record is prepared by Mr. D. P. Todd. It is to be hoped that a regular series of photographic records of sun-spots can be made by some one or more observatories in the East, and by at least one on the Western coast. In order to render such observations of the sun complete, the establishment of these stations and one in Japan is required.
Captain J. Waterhouse, of India, publishes a very complete account (illustrated with photographs) of the preparations by himself and Tacchini to observe the solar eclipse of 1875, April 6, in the Nicobar Islands. No photographs of the spectrum of the corona were obtained, on account of cloudy weather, but the details of the methods adopted are of value.
Sir George Airy sends to Nature a list of thirty-seven ancient eclipses which have been computed by Hind, and of which the original manuscript calculations are preserved at the Royal Observatory. The earliest of these is B.C. 885, the latest A.D. 1652. There are twenty-one previous to the Christian era, and sixteen after it, and the whole is a most valuable contribution to chronology and the history of astronomy. Celoria, of Milan, has also published in No. XI. of the publications of that Observatory a discussion of the solar eclipses of 1239, June 3, and of 1241, October 6.
The important total solar eclipse of 1878 will probably be well observed in America. Estimates for $8000 have been submitted to Congress for American parties.
The reductions of the American Transit of Venus observations are in a forward state.
A discussion of the telescopic observations of the late transit of Venus made by the British expeditions has been laid before Parliament. In this preliminary result the internal contacts observed at five stations have been made use of, viz.: Honolulu, ingress accelerated; New Zealand, ingress retarded very slightly; Rodriguez and Kerguelen, ingress retarded; Egypt (Mokattam, Suez, and Thebes), egress retarded ; Rodriguez, egress retarded very slightly; Kerguelen, egress accelerated. The value of the sun's parallax thus found is 8.760", with a probable error of 0.013", corresponding to a distance of 93,300,000 miles, with a probable error of 140,000 miles. According to Christie, of Greenwich: “Although there may be some small corrections to be applied to the individual results for errors in the provisional longitudes used, their amount can be but small, and it is hardly conceivable that the mean value can be sensibly affected. Nor is there any possibility of materially altering the result by another interpretation of the language of the observers concerned. We must, therefore, accept the fact that these observations of the transit of Venus give a value for the sun's parallax which is considerably less than most of those which have been recently put forward, though still decidedly larger than Encke's result. There remain, however, the observations made in India and Australia, which will reinforce the rather meagre results for egress, and also the measures of photographs which promise to give a very accurate value of the parallax."
Deichmüller, of Bonn, has published an investigation of the circumstances of the transit of Venus in 1882; it has been compared with a discussion lately published by Peter, of Leipzig.
Mr. David Gill, of England, has taken up his residence at Ascension Island, for the purpose of making heliometric observations of Mars to determine the solar parallax. The heliometer to be employed is the one used by Mr. Gill in the Transit of Venus Expedition of Lord Lindsay in 1874, in which Juno was observed and the parallax 8.82" deduced. This expedition is of great importance, in many ways, as it is quite possible that from its results the best determination of solar parallax may be had, as the method employed admits of great refinement. The support given to the expedition is also noteworthy, as the Royal Astronomical Society guarantees the expenses, £500, and as many observatories will join in the fixing of the star-places, etc. It contrasts with the unfortunate expedition of Gilliss in 1849–52, who, on his return to the United States from Chili, found that his brilliant labors in the same field, although by a different and less independent method, had been practically in vain, through the feeble support given by Northern obseryers. Mr. Gill will also observe three of the asteroids for the determination of the solar parallax.
The photographs of the transit of Venus obtained by the United States parties have been examined, and all those which were capable of measurement have been read off. They are as follows:
The grand total for both hemispheres is 221 plates. Owing to the great variability of the photographic diameters of the sun and Venus, it was found impossible to make use of any pictures which did not show a complete image of the sun. This excluded several hundred small photographs taken near the times of contact between the limbs of Venus and the sun.
The above-mentioned measurements of the photographs have been so far reduced that the position-angles of Venus, relatively to the centre of the sun's image, and the positions of the sun's image relatively to the centres of the plates, have been tabulated.
Their further reduction is under way, and it is expected that the reduction of all the observations of the transit itself will be brought to a close by the coming spring. It is also hoped that the observations for longitudes of stations will be reduced before the end of the fiscal year, and with the present appropriation.
The question of the best means for determining the solar parallax will receive new light by the publication of the results of the heliometer measures of Juno by Lord Lindsay and Mr. Gill at Mauritius in 1874. The preliminary results obtained show a surprising accordance between the several nights' work, and indicate a parallax not far from 8.82".
Another method promising good results is the observation of Mars and companion stars at the opposition of 1877; and to facilitate the application of this method, Professor Eastman, of Washington, has prepared a carefully selected list of stars for observation on the meridian with the planet during the period from July 18 to October 12, with suggestions as to the method of observation.
At the private observatory of Lewis M. Rutherford, Esq., New York, Mr. Chapman is making a series of photographs of Mars and comparison stars, which are afterwards to be measured. Two or more photographs are taken 3 h. east of the meridian, and the same number 3 h. west, so that from such a series the diurnal parallax may be had.
It is said in Nature, of January 18, that the measurements of the French photographs of the transit of Venus is not progressing favorably, unforeseen difficulties having arisen. Only forty-seven out of one thousand have been measured.
All the observations of the transit of Venus made by Russian expeditions will be collected and published in one vol. ume, which is preparing at the Pulkova Observatory.
PLANETS, ASTEROIDS, AND SATELLITES. Volumes X., XI., and XII. of the Annales of the Paris Observatory bave arrived in the United States. They are mainly occupied with the development of Leverrier's theories of the motion of Jupiter, Saturn, Uranus, and Neptune. Vol. X. contains an important paper by Wolf and André on the “black drop," with experiments. The Observatory has also published a series of six ecliptic charts in continuation of Chacornac's.
Leverrier's researches on the planet Vulcan were concluded early in 1877. After an examination of all probable hypoth