F. IF. Very— A Cosmic Cycle. 97 



Art VIII. — A Cosmic Cycle ; by Frank W. Very. 



[Continued from p. 58.] 



General Theory of Stellar Explosions. 



Three factors enter into the problem of stellar explosive 

 force : (1) Composition, (2) mass, (3) temperature. There 

 must be, first, the presence of substances of an explosive nature 

 and in sufficient abundance ; next, a mass great enough to give, 

 at a certain stage of contraction, a gravitationally produced 

 pressure sufficient to bring on the unstable explosive condition. 

 The second condition may therefore be defined more exactly 

 as contraction depending on mass. The third condition — a high 

 temperature — is in one sense an effect of contraction, and might 

 be included in the second ; but since the unstable condition 

 cannot exist without powerful internal movements within the 

 atoms, we may designate temperature, and its concomitant 

 latent or internal heat, as the immediate antecedent of disrup- 

 tive explosions. 



Two stages of explosive instability may be distinguished : 



(A) That in which the explosive force has sufficient power 

 to rend a star completely into fragments ; and 



(B) That in which the force is only great enough to cast oif 

 fragments of relatively small size from a parent mass. 



It is conceivable that condition (A) may be limited solely by 

 the mass of the star, or, on the other hand, that its composi- 

 tion is also an essential. If some of the elements are more 

 highly explosive than others, the unstable ones will be used 

 up first, and afterwards only minor explosions can occur. In 

 view of the variety in the relative stability of compounds, the 

 second view is the more probable ; and the following argument 

 seems to be decisive in its favor : Since it is certain that our 

 sun has been attended by the earth during ages of quiet ter- 

 restrial development, I shall assume that the sun and stars of 

 its type have entered upon the second stage, which may be 

 distinguished as that of planetary evolution (B), the first stage 

 (A) being described as that of stellar evolution. 



Now Mr. Maunder has shown'"" that, adopting Elkins' paral- 

 lax, Archer us, which is a star of solar type, if of the same 

 intrinsic brilliancy, must have a diameter 82 times that of the 

 sun ; or, taking Mr. Banyard's more conservative statement,, 

 ;; we may probably feel confident that the parallax of Arctuvus. 

 is less than a third of a second of arc, which would give a dis- 

 tance of at least ten light-years, and a diameter for Arctnrus? 

 on Mr. Maunder's assumption with regard to its intrinsic 

 brightness, equal to about five times the diameter of the sun."f 



* E. W. Maunder, Knowledge, vol. xiv, p. 21, 1891. 

 f A. C. Ranyard, Knowledge, vol. xiv, p. 22, 1891. 



Am. Jour. Sci. — Fourth Series, Vol. XIII, No. 74. — February, 1902. 



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