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verted into Right Ascension and Declination, and are given for each star on every plate to thousandths of a second of R.A. and hundredths of a second in Declination. This is a very complete programme, since it makes the results at once available for comparison with other catalogues, but entails much work, and publication is therefore not rapid. Since the original resolution of the organising committee provided only for the publication of rectilinear co-ordinates, most of the co-operating observatories prefer to first publish simply the measures, and to leave the equatorial co-ordinates for later volumes.
It appears from the reports of the Colonial observatories that the measurement of the plates of Zones 41° S. to the South Pole is proceeding. The plates of Zones 24° to 40° S., divided between Cordoba (S. America) and Perth (W. Australia), are being taken, and there is prospect that these will be measured soon. The work both on the Chart and Catalogue is progressing actively at Tacubaya (10 S. to 16° S.).
Enlargements of the chart plates have been distributed during the year by the Directors of the Paris, Algiers, Toulouse, Bordeaux, San Fernando, Tacubaya, and Greenwich Observatories. The total number issued from these observatories is now
It is understood that the Potsdam Observatory does not propose to take the chart plates 32° to 39° N., but that these zones will be undertaken by the Royal Observatory of Belgium.
It would be unfitting to close this note without making reference to the loss that the work has suffered by the death of M. Loewy, Director of the National Observatory, Paris, who was so much associated with the International Chart of the Heavens. Four French observatories are taking part in this undertaking, and within the last few years three of them—Algiers, Bordeaux, and Paris-have lost their Director by death. M. Baillaud, who succeeds M. Loewy at Paris, is the only survivor of the four French astronomers who superintended the work when it was begun.
H. P. H.
Stellar Spectroscopy in 1907.
New Star.-In last year's report, reference was made to the discovery of a star exhibiting the photometric peculiarities of a Nova. Professor E. C. Pickering announced it (H.C.O. Circular 121) as Nova Velorum. The spectrum had not then been observed, but in H.C.O. Circular 131 (Ast. Nach., 176, 255) Professor Pickering announces that Mrs. Fleming has recently found that its
spectrum exhibits bright lines which appear to coincide with bright lines in the later spectrum of Nova Persei No. 2 1901. Many other interesting spectra of red stars have been found in its neighbourhood.
Professor Hartmann has succeeded in photographing the spectrum of Nova Persei No. 2 (1901) with a specially constructed spectrograph. The star was fainter than the eleventh magnitude. The spectrum was obtained with 84 hours' exposure, and was found to resemble the spectrum of the Wolf Rayet star (Ast. Nach., 177, p. 113).
Studies of Special Stars.- -o Ceti.-The bright maximum of this star in December 1906 and January 1907 was well observed by spectroscopists. Father Sidgreaves (M.N., lxvii. 534) ascribes the unusual intensity of the maximum to weakness of the absorption bands, which usually form the main feature of the spectrum. He also records peculiar behaviour of the hydrogen lines. Father Cortie (Astroph. Jour., xxvi. 123) discusses the bearing of recent observations of o Ceti on the question of the temperature of sunspots. Mr. Slipher contributes two notes (Astroph. Jour., xxv. 66 and 235) on the spectrum of this star. He points out that the hydrogen line Ha (C), as well as Hẞ, Hy, and Hồ, appears bright on his photographs, and that the absorption lines of Vanadium are very strong, a fact which is well brought out by a beautiful plate illustrating the spectrum from A 4100 to A 7000 with comparison spectra of Va, Fe, and Na. Mr. Plaskett (Jour. R.A.S., Canada, i. 45, with plate) gives an account of his studies of the spectrum; his measurements of the velocity in the line of sight are in good agreement with those made by Professor Campbell in 1898.
a Orionis.-Mr. Newall and Mr. Cookson (M.N., lxvii. 482) have discovered three absorption flutings in the extreme red end of the spectrum of this star. They also give results of a comparison of sun-spot lines with marked lines in the green region of the spectrum of the star.
B Orionis. Sir N. Lockyer (Proc. R.S., 80, 50) has detected lines attributable to sulphur in the spectrum of ẞ Orionis.
€ Capricorni.-Mr. Slipher (Astroph. Jour., xxv. 285) finds bright lines in the spectrum, and regards the star as likely to prove to be a binary.
a Scorpii.-Mr. Lunt (M.N., lxvii. 487) gives reason for suspecting the presence of tin in the atmosphere of a Scorpii.
a Boötis.—Mr. Lunt (Proc. R.S., 79, 118) has found several lines attributable to Europium in the spectrum of a Boötis, and discusses the evidence afforded by the spectrum of the solar chromosphere for the presence of this element in the Sun.
These careful researches of Mr. Lunt, originating in the detection of small abnormalities in velocity deduced for special stellar lines, afford a good instance of the way in which our knowledge of terrestrial spectra may be helped by studies of stellar spectra.
Two lists of stars, having peculiar spectra, have been issued by Professor Pickering. The first (H.C.O. Circular 124, and Ast.
Nach., 174, 101) relates to 33 stars, of which 18 have been found to be variable stars; the second (H.C.O. Circular 132, and Ast. Nach., 176, 258) relates to 23 stars, of which 15 are found to be variable stars. The long-continued success of the Harvard College observers in connecting peculiar spectra with variable stars serves to emphasise the view that typical spectra are evidences of special states of equilibrium in stellar conditions.
Variable Radial Velocity.-Notes on variability of velocity are given for the following stars :
Orbits of Spectroscopic Binaries.-Orbits have been calculated for the following spectroscopic binaries:
Dr. See (M.N., lxviii., current volume, 201) states that the average eccentricity among visual binaries is considerably more than twice that among spectroscopic binaries, the average value for 30 of the latter systems being o°22.
Dr. Zurhellen (Ast. Nach., 175, 246) contributes remarks on the analytical determination of orbits of spectroscopic binaries.
Dr. Knut Laves (Astroph. Jour., xxvi. 164) describes a simple graphical method based on the use of the hodograph.
Standards of Wave-length.-Messrs. Benoit, Fabry, and Perot (C.R., 144, 1082) have redetermined the number of wave-lengths of the red cadmium ray in a metre. The resulting wave-length of the cadmium ray, viz. 6438.4702, has been adopted by the International Union for Solar Research as the single primary standard for spectroscopic measurements. This value agrees with the previous determination by Michelson and Benoit within one ten-millionth part.
Messrs. Fabry and Buisson (C.R., 143, 165, and 144, 782) have published wave-lengths of 115 standard lines in the spectrum of the iron arc, between the wave-lengths A 2373 and A 6495. This work is a contribution to the plan of co-operation in the determination of wave-lengths of lines, which will be adopted as secondary standards, lines at intervals of 50 Ångström units throughout the spectrum the wave-lengths being determined by the interferometer method, as far as possible with an accuracy of o001 unit.
Herr Eversheim (Astroph. Jour., xxvi. 172) describes his investigations in determinations of secondary standards. He points out that his wave-lengths seem to be all slightly larger than those of Fabry and Buisson, and states that he is looking for the origin of this systematic difference.
The system of tertiary standards at intervals of from 5 to 10 units will be chosen and determined when the secondary system is complete. The wave-lengths of the tertiary standards will be obtained by interpolation between the secondary standards with the help of large gratings.
Dr. Kayser (Astroph. Jour., xxvi. 190) regards the question of the constancy of wave-lengths as decisively settled. Presumbly his statements must be taken as referring to suspected displacements much larger than those attributable to small changes in pressure.
New Spectrographic Installations.-In the publications of the Lick Observatory, vol. ix., parts 1-3, Mr. Wright gives an introductory account of the Mills Expedition to the Southern Hemisphere. A 36-inch pierced mirror is mounted at Cerro San Cristóbal, near Santiago. The Cassegrain mounting has been adopted, and a three-prism spectrograph is rigidly fixed at the back of the large mirror. Mr. H. D. Curtis, who, on Mr. Wright's return to the United States in March 1906, was appointed to take charge of the work, gives an account of recent changes (Pub. A.S.P., xix. 227), and describes (Astroph. Jour., xxvi. 256) the method
adopted for minimising the change of focus of the silvered mirror in the course of the night's work. A refrigerator is applied two hours before sunset to reduce the temperature of the mirror by 5° or 6° C. By this plan the changes of focus have been reduced from about 25 mm. to about 5 mm. in the course of the night.
At the Dominion Observatory, Ottawa, Canada, Dr. King has put the spectroscopic work in the charge of Mr. Plaskett. Great activity is shown both in the careful preparation of the instrumental appliances for giving the best results (Astroph. Jour., XXV. 195), and in measurement and reduction of photographed stellar spectra (Jour. R.A.S., Canada, vol. i.). The spectrograph is attached to an equatorial of 15 inches aperture.
Measurement and Reduction of Observations.-Papers dealing with determinations of orbits of spectroscopic binaries are referred to above in the paragraph on binaries.
Mr. Moore (Pub. A.S. Pac., xix. 13) gives a résumé of methods of measurement and reduction of spectrograms.
Mr. Schlesinger (Pub. Allegheny Obs., vol. i.) describes a method which he has found useful for simplifying the reduction of measure
Colours of Telescopic Binary Stars.-Sir William and Lady Huggins (Astroph. Jour., xxv. 65) call attention to the corroboration which their view, expressed in 1897, receives from Mr. Lewis's discussion of the relative masses of the components of 18 binary stars: "the apparent satellite is in fact the primary of the system (Mem. R.A.S., 56, xx). Sir W. Huggins had suggested in 1897 that the bluish component of a pair might have the greater mass, and for this reason be still at the earlier evolutionary stage.
Theoretical Investigations.-Professor Schwarzschild (Nach. K. Gesellsch. Gottingen, 1906, Heft 1) has suggested a third alternative to isothermal and adiabatic equilibrium in radiating stellar atmospheres. He calls it radiative equilibrium. The problem to be solved is as follows: If in the Sun's atmosphere the various strata are regarded as simultaneously radiating and absorbing, and if convective motions were to cease, what distribution of temperature would have to be reached in the various strata in order that the observed steady flow of energy should be transmitted without further change of temperature? He finds a solution, proves that the equilibrium is stable, and proceeds to show that radiative equilibrium under certain simplified assumptions gives a good account of the observed darkening of the Sun's limb, whereas adiabatic equilibrium fails.
H. F. N.