( 278 ) p. 1 58. Argelander's formula for representing all the observed maxima 

 of Mira Ceti, as communicated to me by himself, is the following : 



days d. / Q^n \ 



1751, Sept. 9, 76 + 331.8363 + 10.5 Sin. (^-E + 86 23') . 



+ 18.2 Sin. (gE + 231 42' ) + 33.9 Sin. 0^E + 170 19') 



Where E signifies the number of maxima which have occurred since Sept. 9, 

 1751, and the coefficients are given in days. Hence, for the year now in 



progress, we have the maximum : 



d. d. d. 



1751, Sept. 9, 76 + 36115-65 + 8'44 12-24 



d. d. 



+ 18.59 + 27.34 = 1850, Sept. 8.54. 



The circumstance which appears most in favour of this formula is, that it 

 represents the observation of the maximum in 1596, (Kosmos, Bd. ii. S. 367; 

 Eng. ed. p. 326327), which, on the supposition of a uniform period, would 

 deviate more than 100 days. Yet the law of the variations of light in this 

 star is apparently so complicated, that in single cases (ex. gr. for the very 

 exactly-observed maximum of the year 1840) the formula still deviates many 

 days (almost 25). 



C 279 ) p. 158. Compare Argelander's Memoir at the secular festival of the 

 Konigsberg University, under the title of De Stella /3 Lyrse Variabili, 1844. 



( 28 ) p. 159. One of the first earnest endeavours to investigate the mean 

 duration of the period of variability of Mira Ceti, is that of Jacques Cassini, 

 Eleinens d'Astronomie, 1740, p. 66 69. 



( 281 ) p. 172. Newton (Philos. Nat. Principia Mathem, ed. Le Sueur et 

 Jacquier, 1760, T. iii. p. 671) distinguishes only two kinds of these sidereal 

 phenomena : " Stellee fixse quse per vices apparent et evanescunt quseque paula- 

 tim crescunt, videntur revolvendo partem lucidam et partem obscuram per 

 vices ostendere." This explanation of the change of light had been previously 

 proposed by Kiccioli. Respecting the caution which should be exercised in 

 assuming the existence of periodicity, see the important considerations of Sir 

 John Herschel in the Cape Observations, 261. 



( 282 ) p. 172. Delambre, Hist, de 1'Astr. Ancienne, T. ii. p. 280 ; and Hist. 

 de 1'Astr. au ISeme siecle, p. 119. 



( 2S3 > p. 174. Compare Sir John Herschel in the Cape Observations, 



