52 PROCEEDINGS OF THE ACADEMY OJ? 



bright and pale white by Webb ; yellow and warm yellow by Mis? Maria 

 Mitchell. 



20. Arcturus. This is one of the stars denominated red by the ancients' 

 In modern times, according to reliable observations, it has changed its color 

 J. F. Julius Schmidt, formerly of Ulmutz, recently made Director of the AstFO- 

 nornioal Observatory at Athens, and distinguished for his observations on 

 variable stars, which he communicated to the Ast. Nach., says, that for eleven 

 years he had considered Arcturus to be one of the reddest of the stars, and, 

 especially in 1841, he had ranked it in color with Mars. To his surprise in 

 1852 he saw it to be yellow, and entirely destitute of any reddish hue. It 

 then appeared to him by the naked eye lighter than Capella. Capella two 

 years before had been described by Humboldt as yellow, with scarcely a tinge 

 of red ; since then Capella has become blue. During the present year, 1863, 

 I have dozens of times and in all weathers observed Arcturus to be decidedly 

 orange, and of a clear, beautiful color. In this I have been confirmed by 

 other observers. The colors of Arcturus may therefore be stated as having 

 been red, yellow and orange. 



References have already been made in this Catalogue to the changes of color 

 in double and multiple stars. The numbers, such as 3 : 7J, immediately after 

 the names of the fallowing double stars, indicate the magnitudes of the com- 

 panions. The authorities are given after the colors. Some of these I have 

 taken from the original papers, and some I have not so verified, but presume 

 them all to be correct. 



21. 95 Herculis, 5 : 5. Hitherto catalogued as a diversely colored pair of 

 stars to an extreme degree: one being described as apple green and the other 

 as cherry red, and also as an astonishing yellow green and an egregious red. 

 In 1856 58 they were nearly colorless and without any diversity of tint, and 

 in this latter manner they were described by Struve in 1832 3, and by Sestini 

 in 1844 5. Hence a probability of their being colorless once in about twelve 

 years." C. Piazzi Smyth.* 



In the November number, 1863, of the Monthly Notices of the Royal Astro- 

 nomical Society, a suggestion is made, from very high authority, that because 

 the changes in the two companions have in all these cases been simultaneous, 

 they are liable to the suspicion of having been produced by instrumental 

 causes. But this apparent simultaneousness of change may have been pro- 

 duced by a real change in only one of them. If the two stars were white and 

 one of them were to change to an " egregious red," then by contrast in close 

 proximity, from the well known principle of complementary colors, the other 

 would necessarily appear green. The operation of this principle has been very 

 conspicuous in this city during political demonstrations and celebrations, when 

 bright red lights have been kept burning in the streets. The ordinary gas- 

 lights all around them have appeared strongly green. It is submitted that this 

 cause for the simultaneous change in both stars is more probable by far than 

 that three different instruments, in the hands of three different men, in three 

 different countries and at as many different periods, should all, from some un- 

 known cause, fall into the same error ; and this not when directed at the stars 

 generally, but only when pointed to a particular one. 



22. Mizar, Zeta Ursa? Majoris, 3 : 4. Both greenish white. Struve. 



White and pale green. Webb. 



Both yellow, the 4 has the deeper hue. Mitchell, 1860, April 30. f 



23. Xi Bootis, 3\ : 6J. Orange and purple. Webb. J 



Pale yellow and Orange. Mitchell, 1862, July 6. 



* See the Proceedings of the British Scientific Association fur 1863. 



t See American Journal of Scienco and Art. July, 1863, for Miss Mitchell's observations. 

 J For several valuable popular papers ou the double sturs, by the Kev. Mr. Webb, see the first 

 f'xjr volumes of the JnteHectua.1 Observer, London. 



[March 



