330 



NATURE 



\Augiist 16, 1877 



Your paragraph is otherwise correct, more so than one in a 



contemporary which said that Italian herdsmen were exter- 

 minating the flower ; tJuy, at all events, are not likely to show 

 such Alpine prowess. Marshall Hall 



Scientific Club, 7, Savile Row, W., August 13 



067? ASTRONOMICAL COLUMN 



The Colours of a Ur?^ Majoris and Arcturus. 

 — Mr. T. W. Backhouse, writing with reference to the 

 periodical change of colour in a Urs;c Majoris, indicated 

 by the observations of Herr Weber, of I'cckoloh, of which 

 mention was made recently in this column, remarks that 

 after watching it for several months he concludes the 

 variation must be very slight. Mr. Backhouse observed 

 wilh a small binocular, power 2i, with which he estimated 

 the depth of colour as compared with /3 Ursac Majoris 

 and [i Urs;c Minoris, which are respectively bluish and 

 deep orange, not the actual colour of the star. Repre- 

 senting the difference between the two stars of comparison 

 by a scale from o to i, "the depth of colour of a Ursa; 

 Majoris only varied from ^ to i; on this scale, so that the 

 whole range of its variations was less than i of the 

 difference between those two stars, probably not greater 

 than can be accounted for by errors of observation. The 

 greatest depth of colour, assuming {i Urs. Maj. and 

 /3 Urs. Min. not to vary, was observed on January 6, 

 March iS, and April 11, which are not long after Weber's 

 times of minimum." Mr. Backhouse adds that if any 

 period is indicated by his observations, it is more likely 

 to be one of three months than any other. 



Herr Weber observed with a Steinheil achromatic of 

 2j; inches aperture and 3^ feet focal length, power, 90. 

 For details the reader may^consult Astroii. Nach., Nos. 

 1663 and 1773. 



Writing on the subject of periodical variation in the 

 colour of a fixed star, we 'recall some observations by 

 Prof. Julius Schmidt, now director of the observatory at 

 Athens, published upwards of twenty years since, from 

 which he concluded that a very marked change of colour 

 had taken place in the light of Arcturus at least in the 

 year 1852, as compared with ancient observations, and 

 indeed with quite recent ones. On March 21, 1S52, while 

 waiting for a meridian observation of Arcturus at the 

 Observatory at Bonn, Prof. Schmidt remarked to his 

 surprise, that this star, which for eleven years previously 

 he had considered one of the most decidedly red stars in 

 the heavens, was, to the naked eye, only yellowish white, 

 or as he says, to speak more correctly, "matt graugelb." 

 During the transit there was no ruddiness cither in a dark 

 or illuminated field, and on going out into the open air 

 and comparing Arcturus with other stars of the first 

 magnitude, he found it light yellow, even Capella showing 

 more colour. A comparison with Mars, which he had 

 often previously made since the year 1841, was no longer 

 possible, as with reference to the colour of the planet, 

 " Arcturus appeared as a white star." Thormann, on the 

 same night, considered the star "a dirty yellow, like the 

 colour of slightly tarnished brass." The star was often 

 observed at Bonn in this year, and though Argelander 

 was at first sceptical as to any variation of colour, at the 

 end of March he was convinced that Arcturus" exhibited 

 no deeper yellow tinge than Capella, and that red was 

 entirely absent." On May 11 Schmidt considered there 

 was hardly an appreciable difference in colour from that 

 of Capella. He considered that the circumstance of the 

 star having lost for a certain time in the year 1852 every 

 trace of redness was no illusion, but was quite confirmed. 

 Arcturus was one of the six invKtj'ijJoi or fitry red stars of 

 Ptolemy, in which list Sirius, now without a trace of 

 ruddiness, v;as also included. 



The difficulty and uncertainty attending observations 

 on the colours of the stars are considerable for 

 reasons which are sufficiently obvious. There is, 

 perhaps, no more striking instance of the little 



value attaching to isolated observations Dr obser- 

 vations not undertaken for the special object, than that 

 afforded by the binary star y Leonis, of which Struve 

 says : " Kst Stella duplex in hemisphajrio boreali pulcher- 

 rima et splendore et coloribus," and the colours he 

 assigned in the " Mensura? MicronietricK," golden for the 

 larger star, and greenish-red for the smaller one, have 

 been repeated with trifling variation of terms by 

 subsequent observers. Yet on the ''date of discovery 

 of the duplicity of the star by Sir W. Hcrschel, February 

 1 1, 1782, we find he assigns for the colours " L. white, S. 

 white, inclining a little to pale red," differences which, 

 but for the reason just mentioned, might well countenance 

 the idea of a total change in the colours of both com- 

 ponents. It may be added that in y Delphini, we have a 

 very similar case. 



The System oi- 40 o- Eridani.— M. Camille 

 Flammarion communicates some measures of 4D Eridani 

 and its companions made early in the present year. For 

 the epoch iS77'i2, the following are the resi:lts of his 

 observations : — 



Stars AD Position 148 o Distance 37"'2 



AE ,, 339'2 ,, 109-9 



AB ,, 1047 ,, 81-5 



BC ,, 1300 ,, 4" ± 



The secular proper motion of the star A is, according to 



Stiuve, in R.A. ... — 216S ... in Deck ... - 342-3 

 Madler, ,, ... - 2l8'8 ... ,, ... - 3470 



And as M. Flammarion remarks on allowing for the 

 proper motion of the principal star. Prof Winnecke's 

 measures at the epoch i864'84 compared with his own, 

 show that the stars D and E do not form part of the 

 physical system of 40 Eridani. His measures of A B 

 agree with Struve's in proving that B, while partaking of 

 the great proper motion of A, is yet approaching it 

 slowly. C continues its rapid retrograde change of 

 position with respect to B, the distance remaining nearly 

 the same, and if the stars be regularly measured with 

 powerful instruments, we must soon have sufficient data 

 for an approximation to the elements of the orbit. When 

 some one of the southern observatories possesses a 

 heliometer, and we do not know of any instrumental 

 addition to an establishment in a more southern latitude 

 from which results of greater interest and importance in 

 this branch of astronomy can be expected, the determina- 

 tion of the parallax of 40 Eridani, and it may be added of 

 e Indi ought to be amongst the first objects to which it is 

 devoted. 



The Third Radcliffe Catalogue of Star.s. — In 

 the late Annual Report of the Rev. R. Main, the Radcliffe 

 Observer, to the Board of Trustees, it is stated that con- 

 siderable progress has been made with the compilation of 

 the third catalogue founded upon observations made at 

 this important astronomical establishment, from 1862 to 

 1870, and additional assistance is proposed for its speedy 

 completion, though no definite time is assignable for 

 publication. The number of stars contained in the new 

 catalogue is 4.389, or nearly twice the number included 

 in the " second Radcliffe Catalogue," which was the first 

 issued by the present director. The same Report men- 

 tions that the planet Mercury had been meridionally 

 observed thirty-nine times during the year ending with 

 June, 1877, a large number considering the difficulty 

 attending the observations ; but it is not the first time 

 that the Radcliffe obsciver has had occasion to report 

 successfully in this direction; some few ) ears since we 

 believe as many as forty-five observations were secured 

 with the transit-circle in the course of the twelvemonth. 



New Minor Planet.— A telegram from M. Slephan 

 announces the discovery of a small planet by M. Borrelly, 

 at Marseilles, on the nth inst. At 8h. 35m. its R.A. was 

 2ih. 19m. 50s., and N.P.D. 105° 59' ; tenth magnitude. 



