140 



NATURE 



[March 31, 1910 



OVR ASTRONOMICAL COLUMN. 



Astronomical Occurrences in April : — 

 April I. 8h. 29m. Minimum of Algol (/3 Persei). 

 II. Venus, apparent diameter 28 •3". 

 16. l6h. cm. Saturn in conjunction with the Sun. 

 20-21. Epoch of April meteoric shower (Lyrids). 

 21. loh. lom. Minimum of Algol (/8 Persei). 

 23. 4h. cm. Venus at greatest elongation (46° 13' W.). 

 25. 5h. lom. to 7h. 31m. Transit of Jupiter's Satellite 



III. (Ganymede). 

 30. Mercury visible as an evening star situated amongst 



the Pleiades. 



The Spectrum of Comet 1910a. — In addition to the 

 •objective-prism spectra, already mentioned in these 

 columns, MM. Deslandres and Idrac secured some spectra 

 of comet 1910a with a slit-spectroscope of great light- 

 _gathering power, which they describe in No. 11 of the 

 Comptes rendiis. 



The series of bands usually ascribed to hydrocarbons and 

 cyanogen, respectively, are fully represented in these 

 spectra, with the exception of the band at X 460. The 

 hydrocarbon bands of the comet's spectrum exhibit different 

 intensities to the similar bands photographed in the labora- 

 tory, with the carbon arc or the Bunsen flame as the light- 

 source, the most refrangible of the blue bands being the 

 most intense. An " unknown " band at \ 402-1 is similar 

 to one which M. Deslandres found in the spectrum of 

 Morehouse's comet, which Prof. Fowler has since traced 

 to some carbon compound at very low pressures, 

 but other " unknown " bands seen in the earlier spectra 

 are not shown in that of comet 1910a. 



Halley's Comet in Japanese Records. — Some exceed- 

 ingly interesting extracts from Japanese records, probably 

 referring to early observations of Halley's comet, are 

 communicated to No. 420 of the Observatory (March, p. 

 129) by Mr. K. Hirayama, of the Tokyo Observatory. 

 They include accounts of comets which appeared in the 

 years a.d. 684, 837, 912, 989, 1066, 1145, and 1222, and 

 •generally give some details as to the direction and appear- 

 ance of the object. The details for the apparition of 1145 

 are especially full, the observer remarking on the 

 peculiarity that the comet itself should remain bright after 

 the disappearance of its tail ; this he explains, four days 

 later, as possibly due to the presence of the moon when 

 the observation was made. The time of perihelion — as 

 calculated by Messrs. Cowell and Crommelin — agrees with 

 the time at which the comet was observed in the year 

 A.D. 912. 



Meteoric Astronomy. — Anyone interested in the observa- 

 tions of meteors, and those amateurs who, without the 

 benefit of elaborate equipment, are seeking a field where 

 observations may become both interesting and useful, should 

 read Mr. Denning's article, on the progress of meteoric 

 astronomy, in the current number of Science Progress 

 {No. 15, p. 444). The writer therein gives a brief outline 

 of the ideas concerning, and the observations of, meteors, 

 and summarises the chief events in meteoric phenomena 

 since 1798. 



The Lyrids, Perseids, and Leonids are especially 

 described, and the association between comets and meteors 

 is concisely discussed. Mr. Denning also mentions that 

 some showers persist, more or less actively, for months, 

 and instances are not wanting where radiants continued in 

 active play all the year round, the apparent position of 

 the radiant remaining practically constant. He also makes 

 it obvious that the study of meteoric phenomena needs 

 recruits ; the field is a large one, the observations are 

 comparatively simple, and the results important. So far, 

 photography has played but a small part, and there is 

 ample scope for useful work by those possessing suitable 

 cameras and a fair amount of persistent patience. 



Stars with Variable Radial Velocities. — A number of 

 observations of stars which have been found to exhibit 

 variable radial velocities are published by Messrs. Camp- 

 bell, Albrecht, and Wright in No. 173 of the Lick Observa- 

 tory Bulletins. Among the twenty northern stars discussed 

 may be noted k Persei, o Ursae Majoris, p Leonis, o. v, t 

 and 6 Draconis, v Lyrze, a- Cygni, 6 Cephei, and C Capri- 

 •corni. Six southern stars, observed by the Chile observers, 



NO. 2I0gj VOL. 83] 



have also shown a variation of velocity in the line of sight ; 

 they are 5 Canis Majoris, j3 Crucis, rj Centauri, a I.upi, 

 y Apodis, and y Scorpii. 



In the same bulletin Dr. Curtis announces that the 

 definitive reductions of the spectrograms of k Centauri 

 confirm the variation of that star's radial velocity. Dr. 

 Campbell notes that thirteen years' observations of 

 Procyon show that the radial velocities do not appear to 

 have varied appreciably in a manner to accord with a 

 period of forty years, more or less ; they seem to harmonise 

 with Dr. Auwers's conclusion that the orbit plane of the 

 system is approximately tangent to the celestial sphere. 

 There is, however, a suggestion of a secondary variation 

 of the radial velocity, of very small amplitude and a period 

 of about seven years, for the confirmation of which further 

 observations are necessary. 



The minimum of the radial velocity of the binary system 

 in the triple system of Polaris is shown, by the Lick 

 observations, to have been passed, and the velocity of the 

 centre of mass of that system appears to be increasing 

 rapidly. Therefore velocity observations of the bright com- 

 ponent of the Polaris system during the next few months 

 promise to have unusual weight in the determination of 

 the period of the third member of the system around the 

 centre of mass of the whole system. 



Precautions Necessary in Photographic Photometry. 

 — Under this title Mr. Parkhurst publishes a paper in the 

 Astrophysical Journal (vol. xxxi., No. i, p. 15) which 

 contains a number of hints useful to all workers in astro- 

 nomical photography. 



During the work on photographic photometry, which 

 has been carried on for a number of years at the Yerkes 

 Observatory, it was found that the measures were affected 

 by a number of errors introduced by differences in the 

 method of development, by lack of uniformity in the photo- 

 graphic film, and by many other causes. These errors 

 have now been fully investigated, and the results of the 

 investigations are given in the present paper, illustrated by 

 numerous curves. As an example of the results, it may 

 be noted that afc one point of the " developer curves " the 

 density given by " pyro " introduces a difference equal 

 to 0-3 mag. from that given by rodinal, whilst in the case 

 of hydroquinone the resulting difference in magnitude 

 amounts to 09. The necessity for rigidly controlling the 

 time of development, the temperature of the developer, and 

 other variables is just as forcibly shown by other curves. 



Observations of Satellites. — No. 172 of the Lick 

 Observatory Bulletin contains the measures, made by Prof. 

 .Aitken during the years 1906-9, of the satellites of Mars, 

 Saturn, and Uranus. In the case of Mars the positions 

 of the satellites are referred to the planet's limb, but for 

 Uranus and Saturn each satellite is referred to another 

 satellite, except in the case of Titania. The positions 

 given in the tables are uncorrected, except for differential 

 refraction. 



Photographs of Jupiter's eighth satellite were obtained 

 at Greenwich on January 19 and February 11, and the 

 resulting positions, showing fair agreement with the 

 ephemeris, are published in No. 4393 of the Astronomische 

 Nachrichten. 



RESEARCHES ON ALLOYS.' 



'HP HE report referred to below was presented to a meeting 

 -^ of the Institution of Mechanical Engineers on January 21. 

 The report itself is a memoir of some 175 pages and six- 

 teen plates, and embodies the results of researches carried 

 out during a period of two and a half years at the National 

 Physical Laboratory. These researches constitute a con- 

 tinuation of the previous work of Messrs. Carpenter arid 

 Edwards on the allovs of copper and aluminium as re- 

 corded in the eighth report to the .Alloys Research Com- 

 mittee. Owing to the magnitude of the task which would 

 have been involved in undertaking a complete study of a 

 ternarv system of alloys, the authors at the outset decided 

 to limit their investigations to those regions of the system 



1 Ninth Report to the Alloys Re^iearch Committee of the Institution of 

 Mechanical Engineers, by Dr. Walter R"=enhain and Mr. F. C. A. H. 

 Lantsherry, on "The Properties of Some Alloys of Copper, Aluminium and 

 1 Manganese." 



