68 ILLINOIS STATE ACADEMY OF SCIENCE 



diation and enter upon another excursion through the 

 organic world. This process is familiar to us, but we 

 know nothing of the process by which the radiant energy- 

 builds up the organic molecule. The assumption that it 

 does so in some manner fits in with our knowledge of the 

 facts in the case and we are content to leave the details 

 for future investigation. So with the restoration of 

 the atom. If such an assumption fits in with the facts 

 with which we are acquainted we can leave the details 

 of the process for future study. 



"We have already adopted the postulates that the 

 physical universe is infinite; that the distribution of 

 matter throughout space is uniform in the sense that the 

 limiting density of any sphere, as the radius of the 

 sphere increases indefinitely, is not zero; and that that 

 portion of the physical universe which comes under our 

 observation is not essentially peculiar. It follows from 

 these postulates that the distribution of stars through- 

 out space also is uniform in the same sense. If it be 

 assumed further, as is quite commonly, often uncon- 

 sciously, done, that radiation suffers no loss in its trans- 

 mission through space, then the entire sky should be as 

 bright and hot as the disk of the sun. The total amount 

 of radiation which we w^ould receive would not be affect- 

 ed by cosmic dust and obscuring nebulosity, for the only 

 effect which these things would have upon the radiation 

 would be to increase the wave lengths, changing the 

 light waves to heat waves without any change in the 

 total energy of the radiation. As it is a commonplace 

 of observation that the skies are dark and cold it is evi- 

 dent that at least one of the above assumptions must be 

 abandoned. We prefer to abandon the assumption that 

 radiation suffers no loss in its transmission. The fact 

 that there is no sensible loss in such distances as are 

 encountered in the solar system is no deterrent, for these 

 distances, great as they are, are veiy small where inter- 

 stellar or intergalactic dimensions are under considera- 

 tion. 



The energy of radiation cannot disappear, however, 

 without doing work, for the conservation of energy is a 



