Report on the Progress of Chemistry, 



149 



too noble a fruitage is being gathered to permit the thought 

 that the tree is either trunkless or rootless. 



The atomic theory and the theory of quantivalence seem 

 to be generally regarded as the foundation of modern chem- 

 istry, as truly as the undulatory theory is the foundation 

 of the science of optics, or as the theory of molecular 

 motion lies at the bottom of the science of heat, or, per- 

 haps we may add, as the theory of gravitation is at the 

 foundation of astronomy. 



Passing now from these foundation principles to others 

 scarcely less important, we notice in the first place some 

 investigations made in the interesting department of spec- 

 trum analysis. This branch of chemical science is under- 

 going a rigorous examination. Erroneous inductions are 

 being corrected and the conditions under which this kind 

 of analysis can be applied with certainty are rapidly being 

 defined. The fundamental principle, announced by Bun- 

 sen and Kirchoff in their first memoir, that the same ele- 

 ment always gives the same set of bright lines must now 

 be modified by adding the words, when burned under the same 

 conditions of temperature and pressure. For it has been found 

 (see Quarterly Journal of Science, Jan., 1871) that the high 

 temperature or the high pressure spectrum of an element 

 may differ essentially from that of the same element when 

 the temperature or pressure is low. The spectrum of so- 

 dium, for example, when the metal is burned at the tem- 

 perature of a Bunsen flame, consists of a double yellow 

 line only, but when burned in the more intense heat of the 

 electric arch, the same metal yields a spectrum of no less 

 than five lines, each like the first yellow one, double. The 

 extra lines appear one after another as the temperature 

 gradually rises. The sodium spectrum is by no means the 

 only example of this curious effect of high temperatures, 

 And then as to pressure, it is found, in the case of nitrogen, 

 for example, that at a pressure much below that of the 



