Page images

Chinese astronomers, as far back as the year 18 A.D. These observations consist for the most part of approximations (appulses) of the planet to stars. M. Le Verrier, the eminent French geometer, has tested many of these Chinese observations by the best modern tables of the movements of Mercury, and finds, in the greater number of cases, a very satisfactory agreement. Thus, on June 9, 118, the Chinese observed the planet near a cluster of stars in the constellation Cancer, usually termed Præsepe; the calculation from modern theory shows that on the evening of the day mentioned, Mercury was less than 1° distant from that group of stars.

" Although the extreme accuracy of observation at the present day renders it unnecessary to use these ancient positions of the planets in the determination of their orbits, they are still useful as a check upon our theory and calculations, and possess, moreover, a very high degree of interest on account of their remote antiquity."* La Place

says: “A long series of observations were doubtless necessary to recognise the identity of the two bodies, which were seen alternately in the morning and evening to recede from and approach the Sun; but as the one never presented itself until the other had disappeared, it was finally concluded that it was the same planet which oscillated on each side of the Sun.” Arago considers that “This remark of La Place's explains why the Greeks gave to this planet the two names of Apollo the god of the day, and of Mercury the god of the thieves, who profit by the evening to commit their misdeeds.”

The Greeks gave Mercury the additional appellation of orixpwr, the sparkling one. When astrology was in vogue, it was always looked upon as a most malignant planet, and was stigmatised as a sidus dolorosum. From its extreme mobility, chemists adopted it as the symbol for quicksilver.

So difficult is it, in a general way, to see Mercury, that Copernicus, who died at the age of 70, complained in his last moments that, much as he had tried, he had never succeeded in detecting it, in consequence, as Gassendi supposes, of the vapours prevailing near the horizon on the banks of the Vistula where the illustrious philosopher lived. An old English writer, of the name of Goad, in 1686, humorously termed this planet "a squinting lacquey of the Sun, who seldom shows his head in these parts, as if he were in debt.”

In computing the places of Mercury, the tables of Baron de Lindenau, published in 1813, are commonly used. May 25, 1866.


* Hind, Sol. Syst. p. 23.


Seventh Meeting, May 10, 1866. WARREN DE LA Rue, Esq., F.R.S., Vice-President, in the Chair.

Thirty presents were announced, and the thanks of the Society voted to the donors. Dr. Forster,


Lieutenant Safford, and
Dr. Auwers,

M. Herman Goldschmidt, were balloted for and duly elected Associates of the Society. H. Boys, Esq.,

J. E. Saunders, Esq.,
Samuel Hunter, Esq.,

J. T. Slugg, Esq.,
Wm. Barker, Esq.,

E. C. Tuffnell, Esq., and
John Smith, Esq.,

The Rev. H. S. Toms, were balloted for and duly elected Fellows of the Society.

The following papers were read :

Occultations of Stars by the Moon, and Phenomena of Jupiter's Satellites, observed at Greenwich from April 1864 to April 1866 : by the Astronomer Royal.

On a supposed Observation of Biela's Comet : by Mr. Buckingham.

At the meeting of the Society in March, the author having mentioned that he believed he had observed this comet, was requested to give the detail of his observation, which he now did. On the oth of November 1865, about 9*32 G.M.T., he saw two faint cometic bodies in his large refractor, and, by comparison with a small star near, obtained the approximate positions, which he recorded. He explained that his instrument was generally prepared for micrometric observations; but having been absent from home, he was looking for the comet with his 9-inch achromatic and Hind's ephemeris, but could not find anything. He then used the larger instrument, and saw two nebulous bodies, the smaller being brighter; and, not having the micrometer with him, took some transits of the bodies and the small star. Having left town, on his return he could not find the comet again, but detected the small star, and from its place deduced that of the comet.

Mr. De la Rue said it would have been most important to secure a real observation of Biela's Comet; and although the bodies seen by Mr. Buckingham might not have been that comet, it was desirable to record the observation. Seeing Mr. Hind present, he inquired his opinion of their identity.

Mr. Hind said that, considering the comet was then getting brighter, and had been diligently searched for at Rome, Pułkowa, Copenhagen, and elsewhere, with large telescopes without success, he thought Mr. Buckingham had not observed Biela's Comet. In fact, he had no faith in its being that body.

Mr. Stone asked whether Mr. Hind considered the object seen by Mr. Talmage on November 4th to have been Biela's Comet ?

Mr. Hind said he thought so at first, as the position answered well; but inasmuch as it should have been better seen afterwards, and had not been found, he now thought it had entirely escaped observation.

Mr. De la Rue requested Mr. Hind to send a note in writing of this opinion.

Mr. Hodgson said he believed M. Chacornac, of Marseilles, had the largest available instrument for this sort of work—a very large reflector.

Mr. Hind thought Professor D'Arrest's refractor, at Copenhagen, was the best telescope that had been employed in the search.

On a Motive Power for an Equatorial Mounting of an 18-inch Telescope: by Lord Oxmantown, communicated by Lord Rosse.

The arrangement described was a species of clepsydra, consisting of a float falling in a box full of water as the liquid ran out, the description of which would not be intelligible without the drawing which accompanied the paper.

Mr. De la Rue said it was not always the mantle of a father descended on a son; but it must be most satisfactory to the Society to find Lord Rosse would be succeeded by such a son as Lord Oxmantown. Many contrivances had been devised for moving equatorials, and some had certainly before employed water flowing from a pipe. Although he thought such contrivances were not equal to a well-made driving clock, they were capable of following a star with a great approach to accuracy.

Captain Noble pointed out that water clocks were liable to freezing in our climate.

Mr. Hodgson said we should remember that the equatorials both at Greenwich and Liverpool were driven by water power.

Mr. Stone observed that the Greenwich instrument had occasionally been stopped by frost.

General Shortrede suggested the use of oil.

Mr. De la Rue: Unfortunately, oil oxidizes rapidly when agitated, and becomes thick. I have used water as a resisting medium for regulating my driving clock, and have been inconvenienced by its freezing. I tried mercury, but it rose in fine dust, which was injurious to my mirrors, and might be prejudicial to health.

Mr. Huggins inquired whether glycerine would be available ?

Mr. De la Rue said it was very hygrometric, and soon attracted water, which rendered it no better than that liquid.

Professor Selwyn drew attention to a little contrivance suggested by the hypothesis that the position of the planets had some connection with the configuration of the solar surface. When at Rome, he met Professor Volpicelli, who had published some letters of Galileo, which contained passages supporting the theory of such influence, through which Galileo had afterwards run his pen, as not thinking the evidence in support strong enough ; but finding the idea now taken up by Wolf and the Kew observers, the professor had reprinted the letters as first written. Professor Selwyn's plan was to have circles representing the orbits of the planets lithographed on cards, and by placing these at the back of the solar autographs, and marking the places of the planets for the day, when the pictures were held before a looking-glass the sun-spots were seen by direct vision, and the places of the planets by reflection, at the same time.

A Member inquired why Saturn's orbit was omitted ? Professor Selwyn: Because it is not taken into account at Kew.

The Member said that Mr. Procter stated that when Jupiter and Saturn were in conjunction the effect was greater than when in quadrature.

Mr. De la Rue said we saw, not for the first time, the advantage of having many workers in the same field. It was not the first occasion on which we were indebted to Professor Selwyn for valuable suggestions, and he offered him the warmest congratulations on his continued success in photoheliography.

The Chairman said: You will remember the great interest excited by Mr. Airy's paper at the last meeting, and by Mr. Adams's remarks upon it. Since then I have received a letter from Dr. Gould, of the United States, calling my attention to the omission by me of any reference to a paper in his Journal, from which it would appear that M. Delaunay had been anticipated in his theory. I have handed the paper to Mr. Cayley, who will kindly favour us with some account of it.

Mr. Cayley : The paper is dated 8th December 1853, and is by Mr. Ferrall, and is a complete anticipation of Delaunay's fundamental theory. He points out the effect of the moon raising the water on opposite sides of a sphere, and that the small residual force has a tendency to affect the axial rotation. It acts on the water alone, but being resisted by the solid nucleus of

[ocr errors]

the earth, affects the rotation ultimately as if direct. He finds that a tide of 2 feet high, 2 hours after the moon is on the meridian, produces an effect of 84" in a century on the moon's mean motion, and that a smaller tide of 2 inches would give a result of 6'. As at this time it was not known that 6" per century of the moon's acceleration had to be accounted for, the author seeks to neutralise the effect he has found, and assumes that the earth is a cooling body, and has a radius diminishing in consequence, which causes a retardation equal in amount; but Mr. Adams has now shown that 6" of the acceleration is still unaccounted for by the known causes of the influence on the moon's mean motion. The author has evidently travelled over exactly the same ground as Delaunay.

The Chairman was much obliged to Mr. Cayley for his excellent abstract of the paper, and requested him to publish it in the “Monthly Notices.' Mr. Stone wished to know whether the author of the


in Gould's Journal had considered the question whether a part of the force might not be used up in modifying the ocean currents ?

Mr. Cayley : He has not done so.

Mr. Stone thought it not improbable that some of the force was thus expended.

On the Spectrum of a Orionis : by P. Secchi. The author stated that his last too short letter had occasioned some remarks by Mr. Huggins, upon which he desired to say a few words. There was no slit in his spectrum apparatus, as upon stars he considered its operation unnecessary.

The measures were taken in the same way as those of double stars. The strong lines were measured directly with the micrometer, the fainter ones by opening the wires one revolution, and drawing those lines which appeared between. The position of the lines with respect to the colours of the spectrum was also considered correct. The lines D and b had been identified by a spectroscope, showing the lines of sodium and magnesium. The observations of the author had been verified by other observers whom he had asked to check his statements. He thought that his drawing was correct, and wished Mr. Huggins to re-examine one particular band in the spectrum, with a view to verify his statements. He also felt that he had nothing to retract as to the lines in Sirius and Rigel, the comparison of which to Plucker's drawings of sulphur and nitrogen spectra had been commented on by Mr. Huggins.

Mr. Huggins said that Dr. Miller and himself having made their remarks on Father Secchi's former letter, they hardly thought it necessary to make any fresh statements tending to produce controversy in the Society's notices. He would, however, mention that å slit, or some equivalent, was neither useless

« PreviousContinue »