146 LIGHT SCIENCE FOR LEISURE HOURS. 



gen exists in the atmosphere of Uranus. It will indeed 

 be readily inferred that this must be the case, when 

 the fact is noted that no signs whatever of the exist- 

 ence of nitrogen can be recognised in the spectrum of 

 Uranus, though it is difficult to suppose that nitrogen 

 is really wanting in the planet's atmosphere. Dr. 

 Huggins also notes that none of the lines in the spec- 

 trum of Uranus appear to indicate the presence of 

 carbonic acid. Nor are there any lines in the spectrum 

 of Uranus corresponding to those which make their 

 appearance in the solar spectrum when the sun is low 

 down, and is therefore shining through the denser 

 atmospheric strata. Most of these lines are due to 

 the presence of aqueous vapour in our atmosphere, 

 and it would seem to follow that if the vapour of 

 water exists at all in the atmosphere of Uranus its 

 quantity must be small compared with that of the free 

 hydrogen. 



Admitting that the line seen by Dr. Huggins is 

 really due to hydrogen a fact of which he himself has 

 very little doubt we certainly have a strange discovery 

 to deal with. If it be remembered that oxygen, the 

 main supporter of such life as we are familiar with, 

 cannot be mixed with -hydrogen without the certainty 

 that the first spark will cause an explosion (in which 

 the whole of one or other of the gases will combine 

 with a due portion of the other to produce water), it 

 is difficult to resist the conclusion that oxygen must be 

 absent from the atmosphere of Uranus. If hydrogen 

 could be added in such quantities to our atmosphere 



