260 THE CHEMISTRY OF THE SUN. [CHAP. 



gives us a green line only when the weakest possible spark 

 is taken in hydrogen inclosed in a large glass globe, it also 

 proves that calcium is identical with its salts. For we can get 

 the spectrum of any of the salts alone without its common base, 

 calcium, as we can get the green line of hydrogen without the 

 violet one. Hence the argument founded on the overnotes of a 

 sounding body, such as a bell, cannot be urged by any one who 

 believes in the existence of any compound bodies at all, because 

 there is no spectroscopic break between acknowledged com- 

 pounds and the supposed elementary bodies. The spectroscopic 

 differences between calcium itself at different temperatures, is 

 as great as when we pass from known compounds of calcium 

 to calcium itself. There is a perfect continuity of phenomena 

 from one end of the scale of temperature to the other. 



We next saw that common lines had been observed in the 

 spectra of various substances under conditions which seemed to 

 put impurity out of the question, and that then another line of 

 inquiry had been undertaken to see if we were not after all 

 dealing with apparent coincidences only. The result of this 

 inquiry was to show that the coincident lines really behaved 

 differently in the sun from the non-coincident ones. 



The view of which we have now to continue the consideration, 

 is, I think, after all but a slight expansion of the present- 

 chemical view. Chemists regard matter as composed of atoms 

 and molecules. The view now brought forward simply expands 

 the series into a larger number of terms, and suggests that the 

 molecular grouping of a chemical substance may be simplified 

 almost without limit if the temperature be increased. A 

 diagram (Fig. 96) will show exactly what I mean, and what, 

 in fact, flows easily from the consideration of the hypothetical 

 furnaces referred to in a preceding chapter. If we assume 

 a very great difference in the temperature which can be 

 brought to bear upon a substance, we may assume that at the 

 highest temperature we have, for simplicity's sake say, a single 



