240 COSMOS. 



(24) Cancri S, R. A. 128 50', Decl. -f 19 34'. 

 Of these two stars, nothing at present can be said. 



Bonn, August, 1850. FR. ARGELANDER. 



VARIATION OF LIGHT IN STARS WHOSE PERIODICITY is 

 UNASCERTAINED. In the scientific investigation of important 

 natural phenomena, either in the terrestrial or in the side- 

 real sphere of the Cosmos, it is imprudent to connect toge- 

 ther, without due consideration, subjects which, as regards 

 their proximate causes, are still involved in obscurity. On 

 this account we are careful to distinguish stars which have 

 appeared and again totally disappeared (as in the star in Cas- 

 siopeia, 1572); stars which have newly appeared and not 

 again disappeared (as that in Cygnus, 1600); variable stars 

 with ascertained periods (Mira Ceti, Algol) ; and stars whose 

 intensity of light varies, of whose variation, however, tile- 

 periodicity is as yet unascertained (as j Argus). It is by no 

 means improbable, but still does not necessarily follow that 

 these four kinds of phenomena 15 have perfectly similar causes 

 in the photospheres of those remote suns, or in the nature of 

 their surfaces. 



As we commenced our account of new stars with the most 



15 Newton (Philos. Nat. Principia mathem., ed. Le Seur 

 et Jacquier, 1760, torn. iii. p. 671) distinguishes only two 

 kinds of these sidereal phenomena. " Stellae fixre quao per 

 vices apparent et evanescunt, qureque paulatim crescunt, 

 videntur revolvendo partem lucidam et partem obscuram per 

 vices ostendere."' The fixed stars which alternately appear 

 and vanish and which gradually increase, appear by turns to 

 show an illuminated and a dark side. This explanation of 

 the variation of light had been still earlier advanced by 

 Biccioli. With respect to the caution necessary in predi- 

 cating periodicity, see the valuable remarks of Sir John Her- 

 schel, in his Observations at the Cape, 261. 



