EOYAL SOCIETY. 



JANUARY, 1864. 



ON THE CLUSTER k CRUCIS, R.A., 12h. 43m. 36s. N.P.N., 149^ 

 25' 31" (34:^5, H) Lac. 1110 (Neb.). By FRANCIS ABBOTT, 

 F R A.S. Read Juue 3i d, 1862. 

 This delightful cluster, " which is estimated by Sir John Herschel to be 

 formed of from 50 to 100 siars," most of which partake of well marked and 

 varied coloi's, forming an object that is scarcely perceptiV>Ie to the naked 

 eye, but when under proper optical influence it is one of the most brilliant and 

 interesting objects in the southern sky. This cluster is not only an object of 

 interest from the extreme beauty of color and arrangement, but with respect, 

 also to certain changes that are apparently taking place in the number, position 

 and color of its component star.s. 



Some hesitation might be felt in following the author of the Cape observa- 

 tions, with the means he employed, were it not for the encouraging invitation 

 that is given for other observers to note any rema'kable change that niay have 

 taken place since those results were published. Having, therefore, no know- 

 ledge of any other observations being made, or popular account published of 

 A Crucis (except that at Feldhausen), 1 have adapted it for comparison with 

 observations now made and given in the drawings"' for the present epoch. 



The color of all the star3, whsre lisbinct color could be detected, is given on 

 the drawing ; the smaller stars, however, from the 10th to the 14th magnitude, 

 are generalized, and all partake of nearly the samecoloi-, — Prussian blue — some 

 with a little more or less tint of red or green mixed with the blue. The same 

 Greek letters have, with one exception, been used in the drawing as those used 

 for the Cape monograph, but not exactly following those used in the catalogue, 

 the letter and number, when in combination, are grouped together in brackets, 

 and intended to show color and position ocly. 



The 75 stars which are given in the drawing were observed and their positioa 

 laid down with a 5-foot achromatic telescope, 4i inch object glass, of excellent 

 quiility ; the power used for the purpose of laying down the position of the stars 

 was 135 ; but for the colors a comet eye-piece of 27 was found preferable. The 

 colors, as well as the positions, were afterwards checked by a 7-foot achromatic, 

 by Dolland. The evening of the 27th of May was chosen for confirmation ; it 

 was a capital night -no moon, quite calm, and the object near the zenith. But 

 with such a night I was not able to bring out, with the means employed, stars 

 of the 15th and 16th magnitude, given in the Cape catalogue. 



In the Cape observations is laid down to the west of e and 5; they 

 are now, however, all three situated in a straight line, which, when 

 continued, reaches the star (, Astralglib line also drawn through a and 

 /3 cuts 5. Bat the two conspicuous stars in the drawing, v and 6, as 

 well as three small stars marked 12 above the belt, are not shown at 

 all in the C;ip© monograph ; there are also two considerable stars, k and 

 A, to the far-west, which are not seen in the Cape description 



The two stars a and $ apparently retain their color,but y has changed 

 from greenish white to bluish purple ; 5, from green to pale cobalt ; €, 

 red to Indian red ; (, green to ultramarine ; <p, marked t in the drawing, 

 from blue-green to emerald-green ; a^, called ruddy, partakes now of 

 much the same color as all the small stars of that magnitude. 



p. S.— On the 25th of April, while observing the accompanying 

 cluster jcCrux. at 8h. 20m. p.m., a remarkably fine meteor crossed the 

 zenith from v, in the constellation Centaurus, to Neb. Major. By esti- 



* The paper was illustrated by a colored drawing:. 



