DESIGN IN NATUEE 251 



that the earth contains exactly that combination, 

 necessary for organic development. But the objec- 

 tion is not a valid one, because each system of sun 

 and planets in the universe has, no doubt, been de- 

 veloped under identical physical laws and from iden- 

 tical substances. They are, more or less, repetitions 

 of each other, so that the number of systems makes 

 no difference, and the earth can only be contrasted 

 with the other planets belonging to our solar system. 

 Now, have the other planets a similar composition to 

 the earth ? As they shine with light reflected from 

 the sun, the spectroscope does not give us any infor- 

 mation on this point, and we can only speculate. As 

 the composition of the sun differs considerably from 

 that of the earth, we have no reason for supposing 

 that all the planets are similar. On the contrary, if 

 the meteoritic hypothesis be true, and if the meteor- 

 ites which now fall on the earth are samples of the 

 meteoritic cloud out of which the solar system was 

 formed, the planets cannot have identical composi- 

 tions, because the meteorites differ considerably from 

 each other, and no two aggregations of them would 

 give rise to similar bodies. If, on the other hand, 

 the present meteorites are not surviving samples of 

 the original cloud, but have been drawn into the solar 

 system after it was formed, then it is impossible to 

 form any opinion on the chemical composition of the 

 planets. 



If, however, we were to suppose for the moment 

 that the chemical composition is uniform throughout 

 the solar system, it would not help us much, for the 

 proportions which would be suitable for the earth- 



