1888.] of the various Species of Heavenly Bodies. 87 



5. Bands wide, but pale. 



No. in 

 D uner 

 Cat. 



Name. 



Max. 



Min. 



Period. 





3 









67 



11 



436 





125 





1-7 

 I 





.ZOO 





127 





6-7 



11 



146 ! 





157 





8 



12? 



266 





231 



P Cygni 



6 



13 



425 





281 





7 



12 



382 









7 



12 



165 





4 





5-6 



< 12—13 



405 





6. Bands thin and pale. 



No. in 













Duner 



Name. 



Max. 



Min. 



Period. 





Cat. 













50 





1 



1-4 



irreg. 





128 



S Urs. Maj 



7-8 



11 



225 





187 





6-7 



11—12 



2A7 





238 













261 





7-8 



13 



137 





A glance at the above tables will show that the kind of variability 

 presented by these objects is a very special one, and is remarkable for 

 its great range. The light may be stated in the most general terms to 

 vary about six magnitudes — from the sixth to the twelfth. This, I 

 think, is a fair average.; the small number of cases with a smaller 

 variation I shall refer to afterwards. A variation of six magnitudes 

 means roughly that the variable at its maximum is somewhere about 

 250 times brighter than at its minimum.* 



I have already indicated that, with regard to the various origins of 

 the variability of stars which have been suggested, those which have 

 been always most in vogue consider the maximum luminosity of the 

 star as the normal one ; and, indeed, with regard to the Algol type of 



* Obtained by the formula L m = (2-512)" . L m + „. 

 For differences of 5, 6, 7 and 8 mag. we get 

 L m = 100 02. L m + 5 

 = 25124. L m + 6 

 = 63111 . L M + 7 

 = 1585 35 . L m + s 

 L„ = light of a star of magnitude m. 

 L m+f< = ,, „ n magnitudes fainter. 



