Very — Stellar Revolutions within the Galaxy. 137 



unable to distinguish between the relative numbers of large 

 and small stars, and can give no numerical estimate of the 

 degree of (mass) condensation. Scheiner derives a relative 

 numerical condensation of 1 : 16 for the periphery and center of 

 the great cluster in Hercules,"^ but Newcomb's ratio of galactic 

 brightness does not favor so marked a variation in the distri- 

 bution of galactic density, at least not unless there are many 

 dark bodies — incipient novae, not yet ready to shine — situated 

 within the galactic streams. The possibility of such dark 

 bodies must of course be admitted, but no estimate can be made 

 of the amount of matter thus concealed. 



(7) If we may assume that the life of a sun surpasses in 

 duration that of a single revolution about the galactic axis, our 

 solar system has endured much longer than is commonly sup- 

 posed by astronomers, and its age is more nearly in agreement 

 with the time estimates deduced from geological reasoning. 

 The suggestion of a galactic year, embracing many millions 

 of solar years, and perhaps attended by changes in meteoric 

 accessions received in different parts of the orbit, which modify 

 the planetary atmospheres and alter their absorptive power for 

 the solar rays, or change conditions affecting the life of plants 

 and animals, is worth considering. Thus, as Sterry Hunt has 

 shown, the amount of carbon stored up by our earth in the Car- 

 boniferous age exceeds that which can have existed at any one 

 time in an atmosphere suitable for supporting life, many times 

 over. Accordingly, during this age, there were probably con- 

 tinual or successive additions of carbon, or its compounds, to 

 the atmosphere ; and the carbon came from regions of space 

 richer in this material than any traversed before or since. 



The Ice age, which has never been satisfactorily explained, 

 may have been produced in the same way either by changes in 

 the sun itself and its radiant power, or by variations in the con- 

 stitution of the earth's atmosphere affecting the atmospheric 

 absorption of solar and terrestrial radiation, and thus controlling 

 surface temperatures. 



(8) The hypothesis of stellar revolutions around controlling 

 galactic centers may be illustrated by the case of our own sun 

 which is assumed to be well on its way toward perigalacteum. 



Since the projection of the Milky Way upon the celestial 

 sphere divides the sphere into nearly equal parts, our sun at 

 present must be near the plane of the ring or spiral of con- 

 densation. Also, since the apex of the sun's way is not over 

 20° from the central line of the galactic stream in Cygnus, the 

 sun is probably moving obliquely at a small angle with the 

 plane of the ring, around some dominant mass. A right line 



*Abhand. d. k. Akad. d. Wissensch. zu Berlin, p. 36, 1892. 



