Note on Photographs of Phoebe, taken at the Royal Observatory, Greenwich.

(Communicated by the Astronomer Royal.)

Photographs of Phoebe have been obtained with the 30-in. reflector on 16 nights, viz.—

The photograph on October 30 was at or very near elongation, and will thus be of special value for a determination of the mass of Saturn, for which this satellite is peculiarly useful, its distance at elongation being about 28'-three times that of Iapetus.

Royal Observatory, Greenwich:

1907 December 13.

Occultations of Uranus by the Moon in 1908, visible at British Observatories. By A. M. W. Downing, D.Sc., F.R.S.

It is hoped that the publication of the following particulars will enable astronomers who are favourably situated to observe some at least of these interesting phenomena, noting any peculiarities of appearance of the planet at the time of occultation that may strike them.

The Transit of Mercury, 1907 November 14.

(Communicated by R. T. A. Innes.)

At Johannesburg, at ingress, thin clouds obscured the Sun and made observation difficult; at egress the Sun was cloudless except for a few moments just before external contact.

At Pretoria the Surveyor-General organised a party, but clouds prevented any useful observations.

The observations made here are tabulated below. The individual observers' reports are as follows:

:

Mr. R. T. A. Innes, using a 9-in. refractor by Grubb, with a sun-diagonal eyepiece :

When I looked at the Sun at 15h 46m 48 sid. (clock) T. Mercury was already about on. At the time of internal contact rather thick clouds were passing, but the planet was never invisible. Internal contact took place, as nearly as I could estimate, at 15h 47m 48, but it was possibly a few seconds later. Heavy clouds passed for a few seconds, making confused definition. At 15h 48m Is the sky cleared, but contact was passed and the planet clear of the limb by part or so. Before egress the planet was carefully scrutinised; it was a mere circular black dot, without any shading; definition was perfect, the Sun's limb being without a trace of serration. Second internal contact was at 19h 8m 568 and was good; last contact at 19h 11m 368 was fair, as some thin clouds were passing.

Mr. W. M. Worssell, M.B.A.A., took part in the observations with his 3-in. refractor and a direct-vision eyepiece :

Ingress definition was very bad, a decided line was seen at 15h 47m 59 sid. T. Egress: suspected black drop at 19h 8m 48, certain black drop at 19h 8m 518; contact passed at 19h 9 os, external contact at 19h 11m 278. Definition medium.

Mr. J. Innes, 3-in. refractor, direct-vision:

Dark glass split during observations, observations uncertain. Internal contact at egress 3h 46m 41°58 stand. clock T., egress 3h 49m 1.5. One-quarter weight has been given to these observations.

Mr. H. E. Wood, M.Sc. 21-in. refractor (Rheinfelder & Hertel), direct-vision:

Good definition, image small; internal contact at egress good, 19h 8m 568 sid. T., last contact at 19h 11m 258 more uncertain.

For the timing arrangements, electrical sounders, connected with the sidereal clock, were placed near the observers. The clock had

been rated by star observations with a transit instrument for five weeks preceding the 14th November, and had a steady rate of 0.28 seconds per day losing. Its correction at 16 hours S. T. on November 13 was +0'56 seconds. Cloudy weather prevented the observation of time stars on the 14th and 15th, but from the clock rate the corrections at the times of observations of the transit on the 14th are +0.84 seconds at ingress, +0.88 seconds at egress. The mean time clock was rated by comparisons with the sidereal clock, and its corrections are 13 seconds at ingress, - I'2 seconds at egress. When the corrections are applied to the above times, reduction to Greenwich mean time made, and the following reductions to the centre of the Earth applied, ingress internal contact +3:4, egress internal contact +309, external contact +31 28, we have ::

The direct-vision observers using the 3-in. telescope had six sun-glasses either blistered or cracked during their observations.

* Mean of "certain black drop" and "contact passed."

Johannesburg Observatory:

1907 November 15.

Observations of the Transit of Mercury, 1907 November 14
By E. T. Whitelow.

Made at Birkdale, Lancashire.

Long. W. 3° 1′ 37′′.

Lat. N. 53° 26′ 48′′.

Neither ingress nor egress was observed, owing to clouds.

A. Direct Observations were made with 73-in. refractor, stopped down to 4-in. A Thorp's polarising eyepiece: power 150. At 12h. 15m. G.M.T., Mercury showed a clean cut, round disc, with no indication of halo or bright spots. The duration of observation was half a minute or so of bright sunshine, and intermittent observations of a few seconds at a time when the Sun was slightly obscured by cloud, perhaps 2 minutes in all.

At 2h. 20m. there was a sudden burst of bright sunshine in a patch of clear blue sky. I put the edge of the Sun just outside the field of the eyepiece, uncrossed the prisms of the eyepiece so as to get the maximum light, and found Mercury in the field. It had much the appearance of Venns when in inferior conjunction, viz. a very thin curved line of light extending about 120° round the planet. There was no trace of this on the side away from the Sun, nor could I see any trace of the dark portion of Mercury contrasted against the sky.

B. Spectroscopic Observation. 12h. 48m. G.M.T.

Instrument 3-in. refractor, Brashear grating, 15,500 lines per inch; 1st order. Power 120 and 180.

The planet was observed on the Sun's disc only, with the slit parallel to the direction of diurnal rotation. Along the centre of

the spectrum was seen a shaded band, consisting of a dark central band B, bordered by slightly lighter margins A, A1. Each was about the width of the central darker band when Mercury was bisected by the slit. To make sure these were not due to dust lines, I pulled the clock slow-motion cord to and fro, and found these margins travelled with Mercury along the slit. I also slightly increased the opening of the slit, to clear it of any possible effect from dust lines. When I moved the telescope up or down in

declination, the central dark band B became relatively narrower than the 'margins A, A1. Fraunhofer lines in A, A1 exactly corresponded with those on the Sun's surface outside these margins. They were, however, very faint, or hazy, and difficult to focus, although lines on the Sun's surface were perfectly defined. I could not say they were wide, and the difficulty of focussing seemed to be due to lack of sufficient contrast as seen on the margins A, A1.

The total duration of the Spectroscopic observations was about 1 minutes of brilliant sunshine and about 2 minutes of haze.

NOTE-November 18, 1907.-The foregoing observations having been submitted to Father Cortie, he suggested that the failure to see a lighter ring when Mercury was on the Sun's disc while making the observation A might be due to the polarised field of the Thorp eyepiece being then too dark to permit it to be seen.-E. T. W.

Observation du Passage de Mercure sur le Soleil le 14 Nov. 1907. Par Robert Jonckheere, Observatoire de Roubaix.

La situation de l'observatoire est approximativement à 50° 40' de latitude et à 3m 198 de longitude Est du méridien de Paris.

L'instrument utilisé pour les observations est une lunette équatoriale de 220 mm. diaphragmée à 150 mm. La distance focale est de 2.50. Le pied est faible et les trépidations rendent difficiles les mesures micromètriques. Le micromètre est bifilaire. Toutes les mesures ont été prises à l'aide d'un grossissement de 150, mais pour les observations visuelles des grossissements divers, variant de 70 à 600, ont été employés.

L'atmosphere pendant toute la durée du passage de la planète avait le zénith complètement dégagé de nuages mais l'horizon était brumeux. Le soleil étant à une hauteur de 30° en moyenne durant l'observation il a été par instants masqué de nuages, et c'est la raison pour laquelle le premier contact intérieur seul a pu étre observé. L'état atmosphèrique n'a pas permis de chercher à constater la présence de la planète avant son entré sur le disque du soleil.

Le 1er contact extérieur n'a pu étre observé et la planète n'a été aperçue que lorsque la moitié de son disque découpait le bord

solaire.

Aucune déformation des cornes n'a été constatée bien que l'image se présentait à ce moment avec une grande netteté.

Aucun ligament ni pont n'a été remarqué au rer contact intérieur.

La planète était beaucoup plus noire que les taches solaires qui, en comparaison, paraissaient bleues. La corde tracée par Mercure était trop boréale pour occulter aucune de ces taches.

Aucun point obscur pouvant étre considéré comme satellite n'a été observé.