20 INORGANIC EVOLUTION. [CHAP. 



The fluted spectra were boldly ascribed to " impurities," but not 

 always wisely, for, to get rid of the difficulty presented by the two 

 spectra of hydrogen, two perfectly distinct spectra were ascribed to 

 acetylene. Again the " bell-hypothesis " was suggested, according to 

 which the spectrum did not depend so much upon the substance as 

 upon the way it was made to vibrate. According to this view the 

 same chemical atom might have a dozen spectra if struck in a 

 dozen differant ways. 



But it was answered that this argument proved too much ; and for 

 this reason. Mitscherlich showed in 1864 that some bodies known 

 to be chemical compounds when raised to incandescence, give us a 

 spectrum special to the compound ; that is, they have a spectrum of 

 their own ; no lines of either of the constituents are seen. 



I showed later that when the temperature was sufficient to produce 

 decomposition, the lines of the elementary bodies of which the com- 

 pound was composed made their appearances according to the tempera- 

 ture employed. And I also showed that precisely the same thing 

 happens with regard to the fluted and line spectra of the same chemical 

 element. We may get the first alone at a low temperature ; we may 

 increase the temperature and dim it slightly, some lines making their 

 appearance ; and next, by employing a very high temperature, we can 

 abolish the fluted spectrum altogether and obtain one with lines only. 



Since then the difference between the two spectra of the same ele- 

 ment was no more marked than the difference between the spectrum of 

 a known compound and its constituents after the compound had been 

 broken up by heat, it was as logical to deny the existence of compound 

 bodies as to deny that more molecular complexities than one were in- 

 volved in spectral phenomena. 



Attacks like these finally caused the chemists to reconsider their 

 position, and some time later, being under the impression, which has 

 turned out to have no justification, that " monatomic " elements like 

 mercury have not fluted spectra, they conceded that the fluted spectra 

 might represent the vibration of the " diatomic " molecule in the 

 " diatomic " elements. This, of course, was to give up the " bell- 

 hypothesis." 



At the time when the differences of opinion arising from the ex- 

 istence of fluted as well as line spectra in the case of many elements 

 were being discussed, solar observations were beginning to bring before 

 us a perfect flood of facts apparently devoid of any law or order. In 

 1866 I threw an image of the sun on the slit of a spectroscope (Fig. 14), 

 in order to observe the spectra of its different parts, and in this way 

 the spectra of sun-spots (Fig. 19) and eventually of prominences 

 were observed. 



