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Nature of the so-called Elements. 105 
But if calcium be a product of a condition of relatively lower 
temperature, then in the stars, hot enough to enable its consti- 
tuents to exist uncompounded, we may expect these constitu- 
ents to vary in quantity ; there may be more of X in one star 
and more of Y in another; and if this be so, then the H and K 
lines will vary in thickness, and the extremest limit of varia- 
tion will be that we shall only have H representing, say X in 
one star, and only have K representing, say Y in another. 
Intermediately between these extreme conditions we may have 
cases in which, though both H and K are visible, H is thicker 
in some and K is thicker in others. 
Professor Stokes was good enough to add largely to the 
value of my paper as it appeared in the Proceedings, by append- 
ing a note pointing out that “ When a solid body such as a 
platinum wire, traversed by a voltaic current, is heated to 
incandescence, we know that as the temperature increases not 
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The result of that appeal is that the line which, according to 
