VARIABLE STARS. 179 



to the observations of Mackay at Calcutta, and Maclear at 

 the Cape, r\ Argus became more brilliant than Canopus, and 

 almost equal to Sirius.* This intensity of light was contin- 

 ued almost up to the beginning of the present year (1850). 

 A. distinguished observer, Lieutenant Gilliss, who commands 

 the astronomical expedition sent by the government of the 

 United States to the coast of Chili, writes from Santiago, 

 in February, 1850 : " tj Argus, with its yellowish-red light, 

 which is darker than that of Mars, is at present next in brill- 

 iancy to Canopus, and is brighter than the united light of 

 a Centauri."f Since the appearance of the new stars in 

 Ophiuchus in 1604, no fixed star has attained to such an in- 

 tensity of light, and for so long a period — now nearly seven 

 years. In the 173 years (from 1677 to 1850) during which 

 we have reports of the magnitude of this beautiful star in 

 Argo, it has undergone from eight to nine oscillations in the 

 augmentation and diminution of its light. As an incitement 

 to astronomers to continue their observations on the phenom- 

 enon of a great but unperiodical variability in rj Argus, it was 

 fortunate that its appearance was coincident with the famous 

 five years' expedition of Sir John Herschel to the Cape. 



In the case of several other stars, both isolated and double, 

 observed by Struve (Stellarum compos. Mensurce, Microm., 

 p. lxxi.-lxxiii.), similar variations of light have been no- 

 ticed, which have not as yet been ascertained to be period- 

 ical. The instances which we shall content ourselves with 

 adducing are founded on actual photometrical estimations 

 and calculations made by the same astronomer at different 

 times, and not on the alphabetical series of Bayer's Uranom- 

 etry. In his treatise De fide TJranometrice Bayeriance, 

 1842 (p. 15), Argelander has satisfactorily shown that Bayer 

 did not by any means follow the plan of designating the 

 brightest stars by the first letters of the alphabet ; but that, 

 on the contrary, he arranged the letters by which he desig- 

 nated stars of equal magnitude according to the positions of 



* Compare Sir John Herschel's Observations at the Cape, $ 71-78 \ 

 and Outlines of Astron., $ 830 {Cosmos, vol. i., p. 153). 



t Letter of Lieutenant Gilliss, astronomer of the Observatory at Wash- 

 ington, to Dr. Fliigel, consul of the United States of North America at 

 Leipsic (in manuscript). The cloudless purity and transparency of tho 

 atmosphere, which last for eight months, at Santiago, in Chili, are so 

 great, that Lieutenant Gilliss (with the jirst great telescope ever cow 

 itructed in America, having a diameter ol seven inches, constructed by 

 Henry Fitz, of New York, and William Young, of Philadelphia) waa 

 ble clearly to recognize the sixth star in the trapezium of Orion. 



