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POPULAR SCIENCE REVIEW. 
we should expect to find on the supposition that the element 
has undergone decomposition at the high temperatures of the 
sun and Sirius. 
By a comparison of the lines of calcium as seen in the 
spectra of Sirius, a Aquilae, and the sun, Mr. Lockyer finds that 
that line which is all important in the spectrum of the first- 
named star has become much less marked in the spectrum of 
the second ; in which, however, a new broad, well-marked line 
has suddenly, as it were, started into being. The characteristic 
line of Sirius, and that of a Aquilae, he regards as probably in- 
dicative of the presence in the former of one, and in the latter of 
another, of those simpler forms of matter into which, on his 
theory, calcium is at these exalted temperatures decomposed. 
Calcium, as we know it, is thus a product of comparatively 
low temperature. If the line spectrum of calcium obtained at 
the temperature of the electric arc be indeed caused by the 
vibrations of the true atoms — as distinguished from the mole- 
cules — of that metal, then the evidence, granting it to be 
trustworthy in all respects, most probably points to a splitting 
up of calcium in the atmosphere of Sirius with the production 
of a form of matter altogether different from anything known to 
us on this earth. 
But it may be urged that even at what are to us exceedingly 
high temperatures, the calcium molecules are not decomposed, 
and that the line of calcium which is so marked in Sirius and 
other hot stars is probably due to the vibration of the calcium 
atoms into which the molecules are resolved at these extremely 
high stellar temperatures. Indeed Mr. Lockyer has himself 
(“ Nature,” x. 90) stated facts which are not inconsistent with 
this view. 
Now, if this theory be adopted, it is evident that the answer 
to be given to the query, Are the elements elementary ? depends 
upon the meaning which is assigned to the term <6 element.” If 
this word be used to designate a substance from which no forms 
of matter exhibiting properties different from those of the 
original forms can be obtained, then the elements are, by our 
theory, not elementary. But if to “ element ” we give a more exact 
meaning, and define it as substance, the molecules of which 
are composed of two or more similar atoms, then the elements 
are, by this theory, truly elementary. 
The controversy regarding the nature of the chemical 
elements turns largely on the meaning which is given to the 
term “ element.” 
If we are to regard the effect of greatly exalted temperatures 
upon the molecules of the elements as consisting in a decom- 
position of these molecules into their (similar) atoms, we must 
be prepared to bring forward evidence in support of the pro- 
