The Cape day-numbers for 1910 have been printed, and copies received at the observatory for distribution.

Mr. Lunt has contributed a note to the Royal Astronomical Society on "The presence of Tin in Stellar Atmospheres."

Meteorological observations, comprising daily records of airtemperature, pressure, wind, rainfall, etc., have been continued throughout the year, and the results, as in previous years, forwarded to the Meteorological Commission, Cape Town.

Seismograph.-The records of the seismograph have been forwarded to Professor Milne, while a duplicate copy, at the request of the German Government, is forwarded to the Consul-General for Germany in Cape Town, for transmission to the central station for the investigation of earthquakes at Strasburg.

Longitude operations. In connection with a proposed telegraphic determination of the longitude of the Island of Ascension, both from Greenwich and the Cape of Good Hope, during the visit of H.M.S. "Mutine" to Ascension in February 1908, Mr. Pett, after leave of absence in England and before his return to the Cape, proceeded to Greenwich and observed on II nights for comparison of his personal equation, both with the Greenwich observers and with Captain Monro, R.N., who will conduct the field operations at Ascension.

Geodetic Survey of South Africa.-The field data of the triangulation connecting the northern end of the 30th meridian arc in the Transvaal with the existing triangulation in Rhodesia, executed by Captain Gorlon, R. E., between October 1906 and January 1907, were received early in the year. The work has been completely reduced at the observatory, and the results forwarded to Sir D. Gill for publication.

The field work in Northern Rhodesia, after being carried as far as Mpange, S. lat. 9° 41', or about 73 miles south of Lake Tanganyika, was abandoned in December 1906, and all field books containing the geodetic data were forwarded to the observatory for reduction purposes. The horizontal and vertical angles throughout the chain have been reduced and adjusted so far as is possible until a definitive length of the base measured in the Loangwa valley is arrived at.

The measurements of this base, as contained in the field books, have been completely reduced and discussed, and the length of the base has been derived in relation to that of the Russian standard bar used in the measurements; this bar has been forwarded to the "Bureau International" for standardisation, and the derivation of the actual length of the base is deferred until the results of this comparison are available.

The reduction of the astronomical observations, comprising latitude observations at 18 stations and astronomical azimuths at 2 stations, is well in hand, the field book data having been completely reduced and all star corrections computed. The discussion of the places of the 581 stars involved is now proceeding, but its completion awaits the re-observation of several of the stars with

the transit-circle, which will be secured during the early months of the current year.

Royal Observatory, Edinburgh. (Director, Prof. F. W. Dyson, Astronomer Royal for Scotland.)

The recording micrometer referred to in last year's report as having been applied to the transit-circle has worked very satisfactorily, and the screw shows no appreciable wear. The observation of zodiacal stars has been pushed on vigorously, more than 4000 observations being made in the year. It has been found necessary to leave out of the observing list a number of stars of low declination which cross the meridian before midnight in the short summer evenings. With these omissions only about 200 more observations are required. As regards the computations, the observations as far as September 30 are reduced to mean place, and to apparent place as far as October 31.

Spectroscopic observations of the rotation of the Sun have been continued on the same lines as in previous years. From July the observations have been made photographically instead of visually. Sanction has been given for the purchase of a larger objective, and a 9-inch object-glass of 36 feet focal length is being constructed.

Forty photographs of nebulæ have been taken with the 24-inch reflector. Difficulties have been experienced with this instrument owing to the shifting of the mirror, which have not as yet been quite overcome.

Seismographic observations have been carried on continuously, and the results communicated to the Committee of the British Association.

Meteorological observations have been regularly made. Two platinum resistance thermometers have been obtained and placed, one horizontally, the other vertically, in the rock at a depth of 3 ft. 9 in. The cracks in the rock allow of percolation of water, and experiments with two thermometers at the same depth was advised by Professor Callendar before proceeding to place thermometers at varying depths. Observations have been made daily since November 15.

Arrangements have been made to assist the Perth (Western Australia) Observatory in the measurement of the Astrographic plates. A micrometer has been obtained, and 100 plates have been received from Mr. Cooke.

The observatory has lost the services of Dr. Halm, who was appointed Chief Assistant at the Cape Observatory, and left Edinburgh in May. Mr. Clark was promoted to succeed him. The assistants' posts at the observatory have been placed on a more satisfactory footing, having been made permanent Civil Service appointments, a position formerly only occupied by Mr. Heath, the First Assistant.

Cambridge Observatory. (Director, Sir R. S. Ball.)

1. Meridian Circle.-The Syndics of the University Press have undertaken the printing of the large volume of meridian circle results 1872-1900 mentioned in the last report, and the work is making good progress. At the end of the year printing was completed up to R.A. 2h 30m.

Advance copies of the results of the re-observation and examination of all the single observation stars of the Cambridge A.G. Zone Catalogue (to which reference was made last year) have been communicated to Dr. Ristenpart for incorporation in the Geschichte des Fixsternhimmels. All points of interest which arose have been thoroughly examined, and it is believed that very few discordances remain outstanding.

Observation of Gill's Zodiacal Stars has made good progress during the year, 1532 stars having been observed on 50 nights, with the necessary observations of fundamental stars and instrumental errors. The reductions to apparent place have been much interrupted by the work mentioned above, but are complete in R.A. to 1907 March 19, and in Decl. to 1907 September 10; and the reductions to mean place are complete to 1907 February 7.

Mr. Hartley has been in charge of the meridian circle, and has carried out the greater part of all the above work during the year.

The meridian circle clock, by Hardy, which has been in continual use since 1828, was thoroughly overhauled in 1907 January ; with the exception of slight wear on one of the spring pallets, which should not affect the time-keeping, the clock is in perfect condition.

2. Sheepshanks Equatorial.-Two hundred and thirty-eight plates, each containing four or more exposures, have been taken by Mr. Hinks during the year, in continuation of the series for the determination of stellar parallax begun in 1904. On December 31 sixty fields were on the working list as partly observed, and thirteen had just been removed as completely observed at four or more epochs.

Sixty plates taken at Cambridge, which had been lent to Mr. H. N. Russell, of Princeton, U.S.A., were returned in 1907 April. Further consignments were sent to him of 28 plates in 1907 April and 13 plates in 1907 October, completing the series unfinished on his leaving Cambridge which he has undertaken to measure and reduce.

The new form of colour screen for bright stars has been in use since early in the year and appears to be quite satisfactory.

In preparation for the transit of Mercury on 1907 November 14, temporary alterations were made in the rectangular slides of the breech-piece, so that it became possible to take a series of 64 photographs of a segment of the Sun's limb at intervals of 3 or 4 seconds upon one plate. The sky was completely overcast on the day of the transit.

Mr. Stratton has finished his investigation of proper motions of faint stars in the Pleiades from plates taken at Greenwich, Oxford, and Cambridge; the results were contributed to the Society in 1908 January.

Mr. H. Knox Shaw (Trinity College: Sheepshanks Exhibitioner 1907) became a student at the observatory in 1907 October, and has begun work with the Sheepshanks telescope.

A new measuring machine, to take plates up to 10 x 8 inches, constructed by the Cambridge Scientific Instrument Company, has been brought into use during the year. It is a simplified form of the original Cambridge machine constructed by the same company in 1900, which has given complete satisfaction during its seven years of use.

3. Reduction of Eros photographs.-The first part (to 1900 December 31) of the photographic standard system of comparison stars is now complete, and is discussed in Solar Parallax Papers, No. 6 (in M.N., 1907 December.) The second part is approaching completion. The system responds well, to the tests which have been made upon it, and seems to be well adapted for use in the definitive reduction of the parallax plates.

Definitive places of most of the Crossley reflector comparison stars have been furnished to Professor Perrine. For a certain number the published photographic material was unsatisfactory, and many of these stars were too faint to be measured on Cambridge plates. The Astronomer Royal kindly undertook to measure these stars at Greenwich; he has already communicated the places of a first list of 48 stars, and a second list is under observation at the close of the year. The places of 33 very faint comparison stars used in micrometer observations of the planet have been measured on the Crossley reflector meridian series, and communicated by Professor Perrine.

Systematic corrections have been derived for most of the published series of photographic places of the planet, to reduce them to the new standard system. Printed forms have been prepared for the formation of the equations of condition in the final general solution, and a good deal of the preparatory formation of coefficients is done. A preliminary collection of the micrometric observations has also been made in order to see how far these may be used to strengthen the weak places in the photographic series.

The completion of the standard system of comparison stars made it possible to resume the measurement of the Cambridge photographs of the planet. Thirty-two plates, containing in all 281 images of the planet, have been measured during the year; the number of comparison stars measured on each exposure was about nine. The reduction of these measures is nearly complete. A number of star places required for the completion of the standard system were also derived from these plates.

Mr. Hinks has been aided in this work throughout the year by Miss Julia Bell; and Mr. S. E. Bowd has been engaged on the card catalogue and miscellaneous computing. The expense of this

assistance has been defrayed by a grant from the Government Grant Fund of the Royal Society.

4. Floating Zenith Telescope.-As noted in last year's report, Mr. Cookson has found it necessary to extend the observations with his zenith telescope over two years: enough material has now been gathered, the last photograph having been taken in July. The number of photographs available for determining the constant of aberration is 120. All of these plates have been measured in one position of the plate in the micrometer: about half have also been measured in the reversed position. The rest are now being measured. The reduction of all the measurements is in hand and is being carried out with the assistance of Mr. A. D. Campbell.

5. Reduction of Lunar Observations.-Mr. Stratton has continued his new reduction of Schlüter's observations of the Moon for comparison with Hayn's determination of the constants of the Moon's libration and of the selenographical co-ordinates of Mösting A, and the work is making steady progress.

6. Courses of instruction in practical astronomy, and in field astronomy and trigonometrical survey, have been given by Mr. Hinks during the year.

The Newall Telescope, Cambridge Observatory.
(Mr. H. F. Newall.)

The 25-inch equatorial was used in the early part of the year 1907, with the four-prism spectrograph, in photographing the red end of the spectra of the brighter stars. Special attention was paid to the spectrum of a Orionis in its relation to the spectrum of sunspots. A note on some of the results was communicated to the Society in May (M.N., lxvii. 482).

Experiments have been made and are being continued in photographing star spectra with a diffraction grating, in order to decide whether the lines of the telluric B group can be satisfactorily utilised for determinations of stellar velocities.

Measurement and reduction of stellar spectra was carried on chiefly in the earlier part of the year.

The solar work has been carried on with the Littrow spectroscope and with temporary arrangements of coelostat and image lenses. Meanwhile the permanent mounting for the colostat has been constructed, and was delivered at the observatory in December. It is expected that the new image lens of long focus which is to be used for the solar observations will be completed in time for the work in the spring or early summer.

The Littrow spectroscope has been used for the study of the cyanogen absorption-bands at wave-length 3883 in the solar spectrum. A note on some of the results was communicated to the Society in November (M.N., lxviiii. 2). The instrument has been found very convenient to handle.

The same instrument has been used by Mr. Hubrecht in