NATURAL SCIENCES OF PHILADELPHIA. 97 



Crucis, in the Southern hemisphere, and when seen through a telescope, the 

 very varied colors of its indivdual stars give it, according to Sir John Herschel, 

 " the effect of a superb piece of fancy jewelry." During his residence at the 

 Cape of Good Hope, he made a drawing or map of this group, and stated care- 

 fully the colors of eight of its most conspicuously-colored stars. Just a quarter 

 of a century later, F. Abbot, Esq., in a communication to the Royal Astronomi- 

 cal Society in England, dated, Private Observatory, Hobart Town, May, 1862, 

 describes how this piece of jewelry has changed. Six of these eight stars have 

 now different colors. The changes, according to him, are as follows : 



11. Gamma kappa crucis : Changed from greenish white to bluish purple. 

 There is an error in Mr. Abbot's communication, as printed in the Monthly 

 Notices of the Royal Astronomical Society. The name of this star is there 

 printed nu, instead of Gamma. Sir John's list has no nu. 



12. Delta kappa crucis : has changed from green to pale cobalt. 



13. Epsilon kappa crucis : has changed from red to Indian red. 



14. Zeta kappa crucis : has changed from green to ultra-marine. 



15. Phi kappa crucis : has changed from blue green to emerald green. 



16. Alpha? kappa crucis : has changed from ruddy to the similar color of 

 all the small stars of that magnitude. r 'The smaller stars, from the 10th to 

 the 14th magnitude, are generalized, and all partake of nearly the same color, 

 Prussian blue, some with a little more or less tint of red or green mixed 

 with the blue." 



Arago says that certain of the double stars designated by Sir William Her- 

 schel as having a yellow color, are at present, according to Struve, orange and 

 red. Others, which according to Herschel shone with a perfectly white light, 

 exhibit, according to recent observations, a golden-yellow, red, and even green- 

 ish-blue. These will be added to this catalogue in due time. 



Sirius, Procyon, Capella. The Memoir of Donati brings down the former 

 colors of these stars to a much later date than any authority I had found 

 previous to my communications of Feb. 10th and 17th. In August, 1860, he 

 still classes the two former among the white stars. A very few months after- 

 wards, Sirius was observed by Dr. Wilcocks to be changed. At the same 

 date, also, Donati classes Capella among the yellow stars, but, by the authority 

 quoted in the Proceedings of Feb. 10th, it was blue in September, 1859 ! and 

 had been so I know not how long. After making due allowances for this dis- 

 crepancy, if such it be, these are strikingly sudden changes, but not more 

 impressive than those in the cluster Kappa Crucis, where six out of eight 

 stars had changed their colors in a quarter of a century. Beta Ursa Minoris 

 has often vibrated between yellow and red. The very reliable German observer, 

 Heis, wrote: "I have had frequent opportunities of convincing myself that 

 the color of this star is not always equally red ; at times it is more or less 

 yellow, at others most decidedly red." Captain Berard " had for some years 

 seen Alpha Crucis growing red." The temporary star of 1572 in a few months 

 passed through the colors white, yellow, red, another shade of red, and again 

 a duller white. The suddenness and the variety of the changes a star may 

 undergo, are no reasons against their reality. But all this shows the need of 

 caution on the part of the observer, and how a writer should not publish the 

 color of a star as existing at any date, which color may depend altogether 

 on observations of some prior date. Discrepancies must in this way occur, 

 and in this way we may perhaps account for a discrepancy in Humboldt's 

 Cosmos, Vol. 3, p. 181, where, apparently using an old catalogue, he classes 

 Vega among the white stars, but on p. 183, where he individualizes to prove 

 the existence of blue stars, he says, " the light of Alpha Lyrae is bluish." The 

 discrepancy just shown between Kearney and Donati may, perhaps, be similarly 

 explained. A discrepancy of a different kind appears in the Proceedings of 

 the 10th of February of this Academy. Dr. Wilcocks, in announcing the 

 change of Sirius, gave the present color as violet, but previous to the next 



1863.] 8 



