a A. Young an the Solar Corona. 319 



But if we then consider the leucosphere as a true solar at- 

 mosphere, how can we reconcile its enormous extent with the 

 known smallness of the pressure at its base, determined by the 

 experiments of Lockyer, Frankland, and Wullner? In either 

 of two ways ; first, and perhaps on the whole most probably, 

 this atmosphere may consist of some new kind of matter whose 

 density is far below that of even hydrogen ; or it may be com- 

 posed of matter whose specific gravity {not density) is diminish- 

 ed, annihilated, or even rendered negative by some such solar 

 repulsion as appears to be operative in the formation of a com- 

 et s tail. 



There is no doubt that the hne which characterizes its spec- 

 trum coincides with one of the lines of the Iron spectrum witli- 

 iu the limits of any present means of obsei-vation : and so close 

 a coincidence can hardly be accidental. And yet in the spec- 

 trum of iron, this line is only a faint and unimportant one — 

 one of the last to make its appearance under the stimulus of 

 the electric spark, and so little comparable in intensity with 

 many others in its immediate neighborhood, that Mr. Huggins 

 failed to map it on his spectral chart. 



It is certainly difficult to understand how, if this line be really 

 of the same origin as its fellows, it should remain the sole sund- 

 vor of changes which have been able to exterminate from the 

 spectrum all its more conspicuous associates ; and accordingly, 

 from this point of view, it becomes natural to suppose, as I sug- 

 gested in 1869, that when the line appears in the spectrum of 

 iron it may be due not to the iron itself, but to some associated 

 substance (possibly standing in relation to the pecuhar magnetic 

 properties of this remarkable metal)— some occluded gas, wliieh 

 can also exist free in a state of inconceivable tenuity, as we have 

 It m the leucosphere, and probably also in the streamers of the 

 aurora, and in the tails of comets*— a near relative, so far as 

 gravity is concerned, to the luminiferous ether and to the Ur- 

 stoff of German speculators. 



The view of Mr. Lockyer agrees with this in supposmg the 

 leucosphere to consist of some new form of matter. 



On the other hand, it is to be noted that alterations of pres- 

 sure and temperature do produce in known spectra great 

 changes, somewhat such as would be required in order to reduce 

 fl.o „„„-.-.. , . .. , ., ■ jjne. (But I do 



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 3W of any 



pectrum or ir 

 case where on 



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mimportant lines is the 



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disappear. 



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 somewhat 



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