TIME AND SPACE DOUGLAS 153 



the influence of the " resisting medium " through which it moved, 

 this medium being composed of the vast millions of gaseous particles 

 scattered hither and thither into space about the sun by the cataclys- 

 mic disruption of the tidal arm. 



The formation of satellites by the planets is again an evidence of 

 tidal action, but in this case the sun itself was the tide-producing 

 agency which caused the disruption of the planets when each passed 

 its perihelion for the first time. That some satellites so formed 

 eventually became detached from their parent planets to be captured 

 by other planets is one of the interesting results of the action of the 

 resisting medium. 



Dr. Harold Jeffreys has recently proposed several modifications 

 of the above tidal theory. The outstanding point of difference is 

 that Jeffreys limits the size of the ancestral sun to 40 million kilo- 

 meters in diameter, whereas Jeans had presupposed a much less 

 dense sun of diameter 8,000 million kilometers; the former figure 

 is approximately the diameter of Mercury's orbit, the latter figure 

 is greater than the diameter of the orbit of Neptune. The evidence 

 in favor of the smaller figure seems to be fairly strong. 



UNKNOWN PLANETS 



The point of interest in both these forms of the tidal theor\ 

 is that they led to the belief that our solar system was possiblj 

 unique in the galaxy of stars, because the chance of two stars ap- 

 proaching closely enough to produce tidal disruption — namely 10^* 

 kilometers— was only once in 10^" years, Avhich was the whole age of 

 the galaxy then considered possible. With the much greater time 

 scale now proposed by Jeans, and considering also the much closer 

 packing in those early millions of years, the probability of the close 

 approach of two stars becomes decidedly great. Hence the conclu- 

 sion now reached by Jeans is that of the myriad stars we see about 

 us — not the majority — but a considerable number are probably suns 

 to a family of planets. Like our own solar system in many respects, 

 these numerous other systems may be, yet differing probably from it 

 and from one another in all the details. Whether upon some fav- 

 ored planets in some of these many systems there have been devel- 

 oped physical conditions as on this earth, rendering them fit cradles 

 for the advent of life we know not, and it is beyond the scope of 

 the mathematical physicist and astronomer to speculate further. 



STABILITY OF GALAXY 



An investigation of very great interest has been carried out dur- 

 ing the last year by Dr. Ludvik Silberstein on the question of the 



