Ixviii NOTES. 



shone forth as a star of the 1st magnitude between the years 272 and 127 

 B.C., or between the time of Aratus and that of Hipparchus ? 



( a74 ) p. 155. Compare Madler, Astr. S. 438, Note 12, with Struve, Stel- 

 larum compos. Mensurse microm. p. 97 and 98, star 2140. " I believe," says 

 Argelander, " that it is very difficult to estimate correctly in a telescope of 

 great power of light the brightness of such exceedingly different stars as are 

 the two components of a Herculis. My experience is decidedly against the 

 variability of the companion ; for, in my numerous day observations with the 

 telescopes of the Meridian circles at Abo, Helsingfors, and Bonn, I have 

 never seen a Herculis single, which yet would have been the case, if the com- 

 panion were only of the 7th magnitude when at its minimum. I believe it 

 to be constant 5m. or 5'6m. 



C 275 ) p. 155. Madler's Table (Astron. S. 435) contains 18 stars, having 

 very different numerical elements. Sir John Herschel enumerates, including 

 those alluded to in a note, above 45 (Outlines, 819826). 



C 276 ) p. 156. Argelander in Schumacher's Astr. Nachr. Bd. xxvi. (1848) 

 No. 624, S. 369. 



t 277 ) p. 158. "If," says Argelander, " I take the least light of Algol, 1800 

 January 1, 18 h. 1 m., mean time at Paris, as my zero epoch, I obtain the 

 following table : 



Epoch. Duration of Period. Seconds. 



- 1987 2 days, 20 hours, 48 min. 59.416 0'316 



- 1406 . 58-737 0'094 



- 825 58-393 0*175 

 + 751 58-454 0-039 

 + 2328 58-193 0'096 

 + 3885 57-971 0-045 

 + 5441 55-182 0'348 



In this table the numbers signify as follows -.The epoch of the minimum, 

 on the 1st of January 1800, being zero, the next preceding is 1, the next 

 following is + 1, &c. ; the duration, or interval of time between the epochs 

 - 1987 and 1986, is exactly 2 d. 20 h. 48 m. 59.416 s.; whilst that 

 between + 5441 and + 5442 is 2 d. 20 h. 48 m. 55.182 s. ; the first cor- 

 responding to the year 1784, the last to the year 1842. The final column, 

 with the ; sign, contains the probable errors. That the decrease is becoming 

 more and more rapid is shewn by the last number, as well as by my observa- 

 tions since 1 847. 



