68 THE CHEMISTRY OF THE SUN. [CHAP. 



hypothesis of evolution of chemical forms is contrary to, or in 

 accordance with the views of modern chemistry, we must draw 

 a very wide distinction between chemical theory and chemical 

 fact. 



When we compare the laws given in average chemical text- 

 books with the laws which lie at the root, let us say, of astro- 

 nomy, the candid mind cannot fail to be struck by the difficulty 

 which chemists must have encountered in endeavouring to 

 reduce the face of their science to order, on the hypothesis they 

 bring before us. An outsider thinks, for instance, that the 

 basis of chemistry, or a large part of the basis of chemistry at 

 all events, lies in the fact that the chemist has determined the 

 existence of a certain number of elementary bodies, each of 

 these elementary bodies having a certain atomic weight, and 

 that this atomic weight determines all the constants of that 

 body. Yet we read in chemical text-books that this atomic 

 weight is fixed according to no invariable rule ; indeed, with 

 Kepler's laws and Newton's laws in the mind one comes to the 

 conclusion that it is not too much to say that it is determined 

 by a series of compromises. An outsider would, think that if 

 any one of these elementary bodies were taken as a standard, 

 the weight of an equal volume of vapour of another substance 

 under equal conditions would bear some relationship of a 

 definite character to the atomic weight. This however is not 

 the case. Again, among the questions to be considered as de- 

 termining the atomic weights taken, is an assumed limitation 

 of combination power, a so-called atomicity, according to which 

 one substance is a monad, because it will combine with that 

 same relative proportion of hydrogen which exists in half a 

 water-molecule. Another substance is called a dyad, because 

 it will combine with the same relative proportion of hydrogen 

 which exists in a whole water-molecule, and so on. When we 

 thus begin to class the substances into monads, dyads, hexads, 

 and so forth in fact, when we thus effect a re- classification 



