OP THE EXPEDITION. XXXV11 



May 14. Argus and * Centauri being at the same distance from the meridian, the former is 

 considerably the brighter. 



May 16. i Argus more brilliant than the two stars of Centauri combined. 



May 28. t Argus goes on increasing steadily. With the ruddiness of Aldebaran, its magni- 

 tude is only less than Canopus.* Its change since the close of October has been nearly, if not 

 full half a magnitude. 



June 3. To the unassisted eye the atmosphere is remarkably clear, the "coal sacks" of the 

 via lactea being of startling blackness, i Argus and Arcturus have, approximately, the same 

 color, and though the latter is rather ruddier, the former is considerably the brighter. When 

 compared, they had about the same altitude. 



July 5. i Argus is still as bright as the two stars of * Centauri. 



July 25. i Argus as bright or brighter than the two of Centauri. 



July 28. i Argus is on the wane, and is now very little superior to Centauri. f 



1851, May 18. i Argus certainly not so bright as * Centauri. 

 December 28. i Argus quite as bright as * Centauri. 



1852, January 22. i Argus no brighter than * Centauri. 



May 10. i Argus continued fully as bright as the double star * Centauri as late as the 15th of 

 March last. Some nights I would estimate it a shade brighter ; but when the two were at equal 

 distances from the meridian, it was often impossible to detect any difference with the eye. Since 

 then it has sensibly diminished. It comes nearer to my recollection of Capella, as seen in the 

 northern hemisphere, than any other star.J 



These are all the memoranda recorded, and they fully sustain the impression of Herschel, of 

 a fitfully variable star, to an astonishing extent, with neither settled period nor regularity of 

 progression for its minor fluctuations. The more important gradations of lustre, as those no- 

 ticed only by Halley in 167T, and Mr. Burchell in 1811-15, occur but after long intervals. Since 

 1822, there have been annual watchers of its changes, and none have seen it smaller than a 2d 

 magnitude star. That the astronomer of the northern hemisphere may appreciate the lustre of 

 the binary system, ( Centauri), with which I so constantly compared it, a 1 Centauri neither 

 exceeds /, nor falls below p*. Leonis, which is the more obscure of the two ; * 2 is, as nearly as pos- 

 sible, equal with Antares or Spica, with the decided orange tinge of the former, rather than the 

 silvery radiance of the latter. Lieut. MacRae, on one occasion, estimated them at 4th and 2d 

 magnitudes respectively, whilst I put them up as high as 1 and 1.2, which is certainly nearer 

 the fact, though neither of us ever considered <* 2 so bright as /?. As their distance never ex- 

 ceeded 12" during our stay in Chile, the unassisted eye did not separate them, and their 

 combined light is, perhaps, one third greater than that of Arcturus. 



Our time in Chile was rapidly drawing to a close. Before leaving it, I was desirous to learn 

 something more of its people, topography, and agriculture ; and as it was necessary to save my 

 eyes for the series of observations on Venus, to commence about the close of May, I left- Santi- 

 ago for Talca, soon after terminating the observations on Mars. Almost incessant work during 

 nearly a hundred successive nights, in a climate so dry as to open the joints of wood that had 

 been baked in an oven at home, had left me quite destitute of energy very Chilean in apathy. 

 Provided by considerate friends against most of the discomforts of the road, and instructed by 

 them in all useful matters, the month passed on horseback proved an effectual restorative. 

 Within that time, I visited the third city of the republic in population ; the battle-field of Lon- 

 comilla ; descended the Maule in a boat as far as Constitucion on the sea, and re-ascended it to 

 within fifteen miles of Talca; had an opportunity to see the principal towns in the most produc- 

 tive agricultural provinces, and entered the Andes along the banks of the Cachapual, as far as 



* Letter to Lieut. C. II. Davis, U. S. N. 



t Letter to Hear Admiral Win. H. Smyth, R. N. 



t Letter to Dr. C. L. Gerling. 



$ At rnea epochs, June 15, 1850, and 1852, the differences in right ascension were 11".77 and 1 l".5fi, and of declination 3".25 

 and 1".:!3; the former derived from twenty-four, and the latter from eight observations. 



