526 



KNOWLEDGE & SCIENTIFIC NEWS. 



[Shptember, 1906. 



satellites very remote from their primary and revolving; 

 in orbits of high eccentricity. This is the case with 

 Phoebe, the recently-discovered ninth satellite of Saturn. 

 The position of the satellites of Uranus could not have 

 been predicted by the new theory, but Moulton thinks 

 that " they do not definitely contradict it as they do the 

 ring: theory." 



.'\ satellite mig-ht also, on the new theory, revolve 

 more rapidly round its primary than the primary rotates 

 on its axis. This is the case with Phobos, the inner 

 satellite of Mars, which revolves round the planet in 

 7 hours, 39 minutes, 15 seconds, while Mars' period of 

 rotation on its axis is 24 hours, 37 minutes, 22.66 

 seconds, or over three times as long. This unusually 

 rapid rotation of a satellite formed another objection to 

 Laplace's Hypothesis, but it seems to be consistent with 

 the new cosmogony. 



With reference to the so-called " moment of 

 momentum " of the solar system. Professor Chamberlin 

 has shown that the greater portion belongs to the 

 planets, and that Jupiter alone contains about 95 per 

 cent, of the moment of momentum of the total mass 

 within the orbit of Saturn. This is, according to 

 Moulton, "an inevitable consequence of the spiral 

 theory, but, on the contrary, the whole question of the 

 moment of momentum is a rock on which the ring 

 theory breaks." 



According to the new cosmogony the outer portions 

 of the matter ejected from the original body would evi- 

 dentlv be formed from the surface portions of the star, 

 while the matter which followed would "come mainly 

 from lower depths," and would probably consist of 

 materials of greater density. The smaller planets 

 should, therefore, be cool and of high density, and the 

 larger planets hot and of small density. This is also 

 in agreement with the known facts of the solar system. 

 The average density of Mercury, \'enus, the Earth, and 

 Mars is alxjut 4^ (water= i), while the mean density of 

 Jupiter, Saturn, Uranus, and Neptune is only 1.03, or 

 about that of water. We know that the earth is cool, 

 and that probably Mercury, \'enus, and Mars are so 

 also, while there is good reason to suppose that the 

 large planets are in a highly heated condition. 



On the whole, Moulton concludes that " the spiral 

 theorv is even now a good working hypothesis." It 

 seems to explain satisfactorilv all the observed pheno- 

 mena upon which the ring theory was based, and many 

 others which are in contradiction to Laplace's original 

 hypothesis. " Nothing has yet been found which seems 

 seriously to question its validity." 



The new cosmogony will, of course, raise many very 

 difficult questions in celestial mechanics, and will give 

 a considerable amount of work to mathematical 

 astronomers before it can be placed upon a satisfactory 

 basis; but the work which has been already done by 

 Chamberlin and Moulton shows clearly that the spiral 

 theorv is far superior to Laplace's Nebular Hypothesis, 

 which should now be definitely abandoned and con ■ 

 signed to the limbo of unproved theories. The heavens 

 show us thousands of spiral nebulse, which are evidently 

 in a state of rotation round a central nucleus, but which 

 will probably take ages before they have finally con- 

 solidated into suns and solar systems. But ages are 

 but moments in the evolution of the stars, and we need 

 not expect to find much evidence of rotation and con- 

 solidation during the brief span of human historv. Em- 

 pires rise and fall, dynasties are founded and dissolved, 

 but the heavens move on in their silent course, and the 

 human race will probably have perished before the uni- 

 verse has reached its final destinv. 



The Study of the Cell 

 in the Higher Plants. 



Bv H. .\. II.MG. 



(Continued from page 517.7 



Shortly after the appearance of the spircm stage, the 



long thread of chromatin breaks up into separate 



threads, the number of which is constant for any given 



plant; these threads then take on the form of " loops," 



Y 



1 \\ 



Fig. 6. 



that is, become bent on themseK'es, and travel towards 

 the central part, or equator, of the spindle, where they 

 become ananged as a definite rosette, with the bends 

 towards the centre, which, seen in optical section in a 

 longitudinal section, has the appearance of a dark, 

 central, transverse mass, with projecting portions on 

 either side (see Fig. 6). Tliis is consequently known 



