XXXVI ORIGIN AND OPERATIONS 



observations were made'of tliose in our own, as well as of the comparing stars, in the ephemeiis 

 of the Nautical Almanac. 



During all these fine nights the assistants were making up lost time with the circle, extend- 

 ing their nightly zones to the limit their vision would hear, and adding an average of more 

 than a thousand stars to the catalogue each month. A part of their work at this period was in 

 the 5 immediately surrounding the pole, which was observed in one belt, the slow motion of 

 the stars permitting the circle to be moved through that space without the risk of losing any 

 object. In order to insure this also, the same zone was observed on three successive nights, and 

 after comparison of the several results, every star not recorded on each occasion was specially 

 looked for. The circle was read for every star in the polar belts. One of the 9th magnitude 

 was found which performed its entire revolution within the field of the telescope ! When 

 double, the differences of right ascension and declination, and the magnitudes and colors of the 

 components, were noted. There were quite a number of these last which escaped the sweeps of 

 that eminent observer, Sir John Herschel. 



That our estimations of magnitudes might be comparable, Lieut. MacKae and myself had 

 early referred to small and well-known stars of the British Association catalogue as standards, 

 ascending or descending in the scale of brightness to the extreme magnitudes embraced in it. 

 In like manner, the judgment of Mr. Phelps was based on Mr. MacRae's estimates. The 

 smallest star visible in the telescope of the meridian circle, illuminated for ordinary work, and 

 on good nights, was set down as 12th magnitude. Many of Lacaille's must have varied 

 greatly since the date of his work, and not a few of them may probably have short periods. 

 How many of the sixty, not perceptible by us when sought for, may only have been in the 

 wane, remains for the decision of later astronomers. No doubt a part of these discrepancies 

 may be due to erroneous entries in his observation books, and others to errors since made in the 

 reduction of his work ; but as the case now stands, we have ample data to show that the places 

 of the stars contained in the catalogue (Lacaille's) published under the direction of the British 

 Association are extraordinarily inaccurate. That many of the stars south of the zenith of San- 

 tiago are variable, is established by the fact that our observations embrace quite bright stars 

 not contained in his zones ; and one or two of those not visible when twice sought in the early 

 months of the work, were subsequently observed near their proper places. But the variable 

 star of the southern hemisphere which has most interest is i Argus. Taking into account the 

 surrounding nebula, the contiguous clusters of stars, its color, and changes of brilliancy, there 

 is probably no sidereal object more wonderful. From 1884 to 1838, during which Sir John 

 was at the Cape, it never exceeded Centauri in brightness, and at one time was "a good 

 match with Fomalhaut." In 1677, Halley had rated it as low as a 4th magnitude; in 1751, 

 Lacaille saw it a 2d ; from 1811 to 1815, it had been considered a 4th again ; and subsequently, 

 and up to 1845, it had varied between a not very remarkable 1st and a small 2d. At the last 

 named epoch it exceeded the lustre of Canopus, than which Sirius is the only star more bril- 

 liant in all the heavens. The following records are extracted from our note-books : 



1850, February 9. A bright, clear night, and steady atmosphere. Comparing the brightest 

 visible stars, they rank Sirius, Canopus, >, Argus, Centauri. The yellowish-red light of 

 i Argus is more marked than that of Mars. 



February 13. * Argus apparently less bright than Centauri. 



March 31. , Argus is quite as bright as the two stars of * Centauri, and superior to all 

 except Sirius and Canopus. 



April 15. i Argus approaches the brilliancy of Canopus.* 



April 18. Night cloudless, and without haze. After the observations, careful estimation 

 placed * Argus quite equal with, if not superior in brightness to Centauri. They were equi- 

 distant from the meridian. 



Letter to Hon. F. P. Stanton. 



