134 SIMPLER ORGANIC SUBSTANCES 



demands made on such hypotheses are immeasurably greater. 

 They must give a rational explanation of all aspects of the 

 structure of the solar system, the regularity of the orbits, 

 the distances between the planets, the sizes and masses of the 

 planets, the peculiarity of the distribution of angular momen- 

 tum according to which the Sun, in which 99 per cent of 

 the matter of the solar system is concentrated, nevertheless 

 has only 2 per cent of the angular momentum of the whole 

 system and so on. Moreover, a contemporary cosmogonic 

 hypothesis must not contradict any of the numerous geologi- 

 cal, physical and chemical facts which are now known. 



We have, as yet, no such theory of the formation of the 

 solar system which can satisfy all these demands. Therefore, 

 although the overwhelming majority of present-day workers 

 accept the nebular theory (cf. the review of E. Shatsman"*) 

 they frequently disagree with one another on such important 

 questions as the origin and structure of the primaeval cloud 

 of dust and gas, the mechanism of the formation of aggre- 

 gates within it, and so forth. For example, O. Shmidt 

 considered that the planetary cloud was caught up by the 

 already fully formed Sun ; this happened as it passed through 

 an accumulation of gas and dust in the course of its motion 

 round the centre of the galaxy. According to Shmidt this 

 is the only way in which one can explain the peculiar distri- 

 bution of momentum within the solar system. On the other 

 hand, V. Fesenkov"^ maintains that one cannot look at the 

 problem of the origin of our planetary system in isolation 

 from the general problem of the origin of stars, and that the 

 Sun was formed simultaneously or nearly simultaneously 

 with the planets which surround it and apparently from the 

 same dust and gases. 



In the course of the last ten to fifteen years a number of 

 observations have been made which establish that the inter- 

 stellar dust is not uniformly distributed but that there are 

 separate aggregations of matter of an average extent of two 

 and a half parsecs though they sometimes attain the colossal 

 dimensions of 200 parsecs or more. The mass of these clouds 

 may be 300 times that of the Sun, though B. Bok and E. 

 Reilly"* also discovered small clouds of cosmic dust which 

 are easily visible against a luminous background in the shape 



