384 THE CHEMISTRY OF THE SUN. [CHAP. 



realised in the arc, and contrast, them with those furnished 

 by the sun. 



First, if we wish to observe the spectrum of iron, say, in 

 the arc, we have to begin with cold solid iron in the pole, 

 whereas in the hottest strata of the sun cold iron can only get 

 there by 'accident as it were. In the laboratory the result of 

 the highest temperature, if any special result be produced, will 

 be cloaked, masked, and hidden by all the effects, by all the 

 simplifications, which have been brought about to produce that 

 precise result of the highest temperature. We should get an 

 indication in the arc of the line spectra of all these stages up 

 to the point to which the temperature of the arc is competent 

 to simplify the bodies. 



It is next important to point out that if we integrate all the 

 light coming from every part of the arc as we do when we do 

 not throw an image on the slit, we have this masking of possible 

 results in its most intense form. Further, a reminder is 

 necessary, that as in the case of the sun, we are dealing with 

 a globular mass of vapours and not with a section, hence the 

 reasoning in chapter xxii. applies to this case also. 



We can make either the upper or lower pole positive, and as 

 the charge will always be in the lower one, if any difference 

 in the spectrum is produced in this way, it can easily be 

 detected if an image is used. 



Roughly speaking, the carbons employed give a spectrum 

 containing, besides the flutings of carbon, the lines of calcium 

 and iron, some of them reversed, as I have already shown. 



In the photographs of the arc taken under the conditions I 

 have stated, the calcium lines are generally seen at one pole 

 and some of the carbon flutings at the other. 



The line which is observed in the line of sight, so to speak, of 

 the pole which does not contain the charge is the line which is 

 not produced at the highest temperature. 



That this is a phenomenon not dependent upon the chemical 





