VARIABLE STARS. 177 



Its brightness at ita minimum keeps the mean between v and v of the 

 same constellation ; in the maximum it does not quite reach that of X. 

 It takes 4d. 21h. to attain its full brightness, and 5d. Gh. for its diminu- 

 tion. 



(2-2) (3 Pegasi, R. A. 34'lo 7', Decl. 427^ 1G^ Its period is pretty 

 well ascertained, but as to the course of its variation of light nothing can 

 as yet be asserted. 



(23) Pegasi R., R. A. 344° 47', Decl. +9° 43'. 



(24) Cancri S., R. A. 128° 50', Decl. -\-\90 34'. 



Of these two stai's nothing at present can be said. 



Fr. Argelander. 

 Bonn, August, 1850. 



Variation of Light in Stars whose Periodicity is 

 Unascertained. — In the scientific investigation of important 

 natural phenomena, either in the terrestrial or in the sidereal 

 sphere of the Cosmos, it is imprudent to connect together, 

 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 ap- 

 pe. red 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 (Jeti, Algol) ; and stars whose 

 intensity of light varies, of whose variation, however, the pe- 

 riodicity is as yet unascertained (as rj Argus). It is by no 

 means improbable, but still does not necessarily follow, that 

 these four kinds of phenomena^ 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 

 remarkable of this class of celestial phenomena — the sudden 

 appearance of Tycho Brahe's star — so, influenced by similar 

 considerations, we shall begin our statements concerning the 

 variable stars whose periods have not yet been ascertained, 

 with the unperiodical fluctuations in the light of rj Argus, 

 which to the present day are still observable. This star is 

 situated in the great and magnificent constellation of the 



* Newton {Pkilos. Nat. Priyicipia Mathem., ed. Le Seur et Jacquier, 

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

 phenomena. " Stellae fixsj quae per vices apparent et evanescunt, quse- 

 que paulatim crescunt, videntur revolvendo partem lucidam et partem 

 obscuram per vices ostendere." The fi.xed stars, which alternately ap- 

 pear and vanish, and which gradually increase, appear by turns to show 

 an illuminated and a dark side. This explanation of tlie vai-iation of 

 light had been still earlier advanced by Riccioli. With respect to the 

 caution necessary in predicating periodicity, see the valuable remarks 

 of Sir John Herschel, in his Observations at the Cape, 6 261. 



K 2 



