F. W. Very — A Cosmic Cycle. 107 



It will be seen that the short-period spectroscopic binaries 

 are generally of earlier spectral type and have greater varia- 

 tions of velocity in the line of sight. 



It has been found that the large and irregularly diffused 

 nebulae, as well as the star-clusters, congregate in or near the 

 Milky Way. This remarkable fact has hitherto been without 

 explanation, but it receives one if we admit that both the 

 diffuse nebulae with their branching and curved extensions, 

 and the clusters, which in several instances exhibit irregularly 

 radial linear arrangements of stars, have been produced by the 

 explosion of exceptionally large stars which are consequently 

 most numerous in the Galaxy. May we not say that here also 

 extremes meet, since the presence of a considerable number of 

 these huge explosive stars implies, apparently, an equal pre- 

 ponderance of unusually small stars, the fragments of past 

 explosions ? 



The appearance of rotation in nebulous forms cannot be 

 reconciled with any other than a motion of a relatively tem- 

 porary character. It is inconceivable that these long curved 

 arms should retain even their partial symmetry through any 

 considerable number of consecutive revolutions. They would 

 surely become drawn out and inextricably entangled, if com- 

 pelled to follow the mazes of such movements as occur in 

 binary stars. This accords with the failure to find any change 

 of position-angle in the nebulae.* 



In the absence of proper motion, the combination of motions 

 arising from explosive and centrifugal forces will produce in 

 the disseminated material a symmetrical sigmoid curvature, 

 such as we see in G. C. 3614 = N. G. C. 5217, and with less 

 perfect symmetry in Messier 99, f and in Messier 83,^: where 

 there are three or four branches to the spiral. 



In the absence of rotation, a straight ray of nebulosity may 

 be produced as in 



N. G. C. 676 = G. C. 400 

 " 4216 -- " 2806 



" 4861 = " 3340 



The first of these has a central star, the second a central con- 

 densation, and the third two end stars. 



Extreme vigor of rotation and repeated explosions are indi- 

 cated in such complex forms as the great spiral nebula in 

 Canes Venatici.§ 



According to a sketch made by Mr. Johnstone Stoney with 

 Lord Bosse's telescope, April 19, 1849,1 K G. C. 4631 exhibits 



* See Dr. J. L. E. Dreyer in Monthly Notices R. A. S., vol. xlvii, p. 412, 1887. 

 f G-. C. 2838 = N. G. C. 4254. % G- C. 3606 = N. G. C. 5236. 



§ Messier 51 = G. C. 3572 = N. G. C. 5194. 

 || See Phil. Trans. R. Soc. London, vol. cxl, pi. 37, fig. 9, 1850. 



