Second Meeting, December 8th, 1871.

W. Lassell, Esq., F.R.S., President, in the Chair. Secretaries-Dr. Huggins, F.R.S., and E. Dunkin, Esq.

The minutes of the last meeting were read and confirmed. Thirty-four presents were announced, and the thanks of the Society voted to the respective donors.

E. G. Monk, Esq., and

Duncan Darroch, Esq.,

were balloted for, and duly elected Fellows of the Society.
The following papers were announced and partly read :—
Observations of Tempel's Comet: by Mr. Hind.
Elements and Ephemeris of the same: by the same.

Ephemeris of Tuttle's Comet for the Southern Hemisphere: by the same.

Occultation of Vesta by the Moon: by the same.

VOL. X.

This will occur on December 30, the immersion at 10h. 44m., G. M. T., and the emersion at 11h. 52m. G. M. T. record of any similar occurrence before.

There is no

Mr. Dunkin said that it would be useless to look for the immersion which happened at the bright limb of the moon, as the light there was sufficient to obscure 6th magnitude stars before the occultation, and Vesta only appeared of the 7th magnitude, but with fair telescopes the reappearance at the dark limb might be looked for.

On the Floor of Plato: by Mr. Birt.

The author had suspected that the sun produced a darkening effect on the floor of Plato, and upon examining 133 observations by different observers he found this idea confirmed. He had projected the result graphically into a light curve, accompanied by one of the sun's altitude, which showed that after sunrise the tint darkened to the meridian elevation, and then lightened again.

Capt. Noble wished to know how the tints were compared? Mr. Birt: By estimating them as light or dark, and as compared with the adjoining Mare Imbrium.

Capt. Noble But that surface would be similarly affected. You want something external. Was your Homochromoscope used? Mr. Birt No. The tints were derived from the estimations given by the different observers.

The President: Do you not want a standard of comparison in order to project your curve with accuracy ?

Mr. Birt: It would be desirable, but the investigation has not proceeded far enough at present. It is quite clear there is a difference according to the solar elevation. I have noticed this for 11 years, but never had materials for a curve before.

Capt. Noble suggested the employment of a wedge of coloured glass with a graduated edge to measure the tints.

Mr. Birt: Nothing could be better, but it is difficult to get observers to use it.

On the Spectrum of Hydrogen at low Pressures: by Mr. Seabroke.

The author during the summer has been comparing the lines of Hydrogen and the Sun, to see if there were any more lines due to that gas in the chromosphere than those already known. His experiments were made at the Rugby Observatory. The hydrogen tube was connected with a Sprengel pump, and the pressure reduced to 3 or 4 m m of mercury; a battery and coil being used to pass the sparks through the gas. The room was darkened, and sunlight obtained when required by reflection from a heliostat in the roof. The light of the spark was concentrated by a lens on the slit of the spectroscope (which consisted of 4 prisms of

60°) and passed twice through the train. Twenty-one lines were examined, but only the C and F hydrogen lines were found to coincide with any in the chromosphere. In making this statement a line near g and the line h which are known to be due to hydrogen are not included.

Occultation of Capricorni by the Moon, on Nov. 18, 1871: by Capt. Noble.

The star disappeared instantaneously at the dark limb of the moon at 22h. 52m. 31°38. L. S. T.=7h. 3m. 0·7s. L. M. T., and reappeared pretty sharply at the bright limb at 23h. 39m. 88. L. S. T.=7h. 49m. 38.9s. L. M. T. The star being low there was a good deal of undulation.

Eclipse of Jupiter's Third Satellite, on Dec. 4, 1871: by Capt. Noble.

It is impossible to say exactly when the light was first diminished, as it took several minutes to fade out. The last glimpse was at 118.7. Capt. Noble thinks it should be settled what is the eclipse, whether when the fading begins, when the satellite is dichotomized, or when it finally disappears. The latter will not do, as it would be seen so much longer in large telescopes than in small ones. He also again adverted to the inaccuracy of the tables.

The President: The Nautical Almanack tables of Jupiter's phenomena were not intended for large telescopes.

Capt Noble That is true, but it is not the question. I want to know why Damoiseau's Tables, which are admittedly incorrect, are still used in the computations for the Nautical Almanack.

Mr. Dunkin: The Society ought to be very much obliged to Capt. Noble for calling attention to the errors of Damoiseau's Tables. It is easy to say compute new ones, but not so easy to do. With respect to the time of disappearance I have probably seen as many of these eclipses as most people, and I take the disappearance to be when I cannot see the satellite any longer, and the reappearance to be when the first faint light appears which gradually grows stronger. The tables were certainly intended to be used with telescopes of small aperture. The Nautical Almanack is a wonderful work, and the errors are very small indeed in most cases. Even in using these eclipses for the determination of longitude, the present tables would give it within a quarter of a degree as well as the best tables that ever could be made. The errors with the 1st and 2nd satellites which move slowly are very small, with the 3rd they are greater, and the 4th has been even twenty minutes out, but eclipses of this satellite are very scarce indeed. We saw one lately, and I was surprised to find the error was only two minutes.

Capt. Noble That was only a fluke. When we compared the Nautical Almanack with the Greenwich Observations here on a former occasion, we found an error of 19s. with the 1st satellite. Now these eclipses are very sharply seen, and I contend that they could be used for getting the longitude with telescopes of given dimensions, and errors of 19 seconds ought not to occur.

Mr. Dunkin: The observations at present are made with apertures from 3 to 13 inches. With the equatorial, the satellite is seen later, and again earlier than with anything else.

Note on the November Meteors: by Capt. Noble.

During his watch from 12h. to 1h. 15m., on November 13, the author failed to see a single meteor.

Mr. Glaisher said that every minute of the nights of November 13 and 14 was watched by the Greenwich observers, and they only saw 30 meteors in the whole time. Captain Noble's observation was important as showing that we were now well out of the stream of meteors, and not likely to see many for nearly 30 years. As to Jupiter's satellites, the Nautical Almanack represented the tables of the time, and although materials for improving them existed, it could not be said it was Mr. Hind's duty to calculate new ones. It was much to be regretted we generally left foreigners to discuss the results of our excellent observations.

Mr. Ranyard suggested that to rely on such observations, we wanted not only a fixed aperture, but a fixed amount of cloud, and a fixed altitude of Jupiter.

The President: It would require the mean of observations by a number of observers, through a series of phenomena, before we could say the Nautical Almanack failed to do what it professed. Capt. Noble I am not saying the almanack is not well computed; but why are not the tables corrected? If not Mr. Hind's business, I should like to know whose it is?

Professor Cayley suggested that we wanted another thing. The bock represented existing tables, and observations should be obtained for comparison, before attempting to alter it.

Capt. Noble: We want some German, Swede, or other foreigner to make tables which no Englishman can or will do.

Mr. Ranyard: Even with a standard telescope, differences of altitude or other circumstances would make a difference of 1-8th of a degree of longitude.

Mr. Dunkin said that to make the Nautical Almanack a perfect production, the tables of all the bodies must be recomputed. Even the moon sometimes differed from its computed place a second, and it might be different another time, so that a table of corrections had to be used. He thought that the Germans would soon produce new tables of Jupiter, Saturn, and Uranus.

On the Geodesic lines in an Ellipsoid: by Professor Cayley. The author explained this paper orally, illustrating his remarks by a diagram.

Rev. J. C. Jackson read a letter from Mr. Gledhill, accompanying a drawing of Jupiter which was exhibited to the meeting. In 1869, Mr. Gledhill observed a remarkable elliptical formation on the planet which had now reappeared. The drawing was made on December 1, 1871, about 11h. 30m., G. M. T., with an achromatic telescope of 9 inches aperture and power of 240. The ellipse was situated just to the south of Mr. Gledhill's band 4 and was 15" in length. Its shape was regular, and it was preceded by a large whitish spot on the same parallel. It seemed the same configuration as seen before, or else one exactly like it. There appeared to be some connection between this form and the small white spots.

Capt. Noble saw the small white spot last month with his telescope of 4-2 inches aperture.

Mr. Ranyard said that Mr. Gledhill had sent him a copy of the drawing in which was a curious spot like a pipe. This also had been seen before at the same time as the ellipse.

Mr. Proctor exhibited and described his original chart of 324,198 stars. He said that Mr. Brothers had given an account of its preparation and the labour involved, but that was the least part of its importance. Its real use was in assisting us to form proper views of the construction of the heavens. With regard to the objection that the constellations were not readily detected, that was entirely obviated by the accompanying small chart of the configurations.

On Mr. Abbott's imagined discovery of great changes in the Argo Nebula: by Mr. Proctor.

The author being at a loss to understand the conflicting statements on this subject, and the great discrepancies between Mr. Abbott's drawings and those of Sir J. Herschel, had examined them carefully, and believed that he had ascertained the cause to be the difference of scale between the representations. Mr. Abbott's drawings are made with a small telescope, showing a field of 1° 7′ 42′′, while Sir J. Herschel's include very much less of the nebula at any one moment. The effect of this is that the lemniscate, which is so marked a feature in the Cape drawings, is in Mr. Abbott's only of an inch long, and is therefore hardly recognisable. The Orion Nebula, if treated in the same way, could never be identified with the one drawn by Lord Rosse, or with other large telescopes.

On the Motion of Matter projected from the Sun, with special