Humboldt's Letters. 167 



time, quite disproportioned to their apparent extent. 

 However, I have great hopes of being able to get a 

 considerable portion, in the course of the next year, into 

 the printer's hands. Some of the nebulas are already in 

 course of engraving. Perhaps the subject which has 

 given me most trouble is that of the photometric estima- 

 tion of the magnitudes of Southern stars and their com- 

 panions with the Northern ones. A curious fact respect- 

 ing one of them 7 Argus has been communicated to 

 me from a correspondent in India (Mr. Mackay), viz. : 

 that it has again made a further, great, and sudden step 

 forward in the scale of magnitude (you may perhaps 

 remember that in 1837-8, it suddenly increased from 

 2. 1 m to equal a Centauri). In March, 1843, according 

 to Mr. Mackay, it was equal to Canopus. " a Crucis," 

 he says, " looked quite dim beside it." When I first 

 observed it at the Cape it was very decidedly inferior to 

 a Crucis. 



Believe me, my dear Sir, ever yours, most truly, 

 J. F. W. HERSCHEL. 



I must not forget to wish you a " merry Christmas 

 and many happy returns of the season" in English 

 fashion. 



