XIX.] 



EVOLUTION DIAGRAM. 



261 



line represented by a single circle ; let us imagine the tempera- 

 ture reduced, we shall then get another spectrum, which we 

 can represent by a double 

 circle, if we like to assume 

 that the evolution is one 

 which proceeds by con- 

 stant additions of the 

 original unit. Coming 

 lower down, we get an- 

 other substance formed 

 with a more complex spec- 

 trum represented by three 

 circles ; lower down still 

 we have one represented 

 by four circles, another by 

 live, another by six, and so 

 on. We might take another 

 supposition, easier perhaps 

 to some minds, and sup- 

 pose that evolution pro- 

 ceeded, not by the constant 

 addition of the initial unit, 

 A + A, but by the constant 

 doubling of the substance 

 of the molecule itself. In- 

 stead, therefore, of our 

 circles increasing by one, 

 we shall have one, two, 

 four, eight, sixteen, thirty- 

 two, and it will be readily understood that if there are a con- 

 siderable number of stages of temperature, both within our 

 ken and beyond our ken, and if some substances form them- 

 selves perpetually by doubling, then the unit with which we 

 can experiment at low temperature, call it the chemical atom 





