in the Solar Chromosphere. 475 



are present in the high-level chromosphere, we shall have no 

 means of detecting them *. 



As regards Hydrogen, ionized Hydrogen would mean 

 simply the hydrogen core, and this probably by itself would 

 be incapable of emitting any radiation. But as H a and H^ 

 lines occur high in the chromosphere, we have to admit that 

 hydrogen probably is not much ionized in the chromo- 

 sphere. 



The case of helium is very interesting. It is well known 

 that the Fraunhofer spectrum does not contain any helium 

 lines, which are obtained only in the flash spectrum. But 

 these lines are all due (o normal helium, and the highest 

 level reached by the second line of the so-called principal 

 series is some 8500 kms.f, while the better-known D 3 

 reaches a level of 7500 kms. The lines due to ionized 

 helium are represented by the general series formula 



v = 4N 



1 _ll 

 .m 2 n 2 



and the best known of them, in the visible range, are the 

 Rydberg line -ItiSG and the Pickering system 



»=*[h-tdwi 



once ascribed to "cosmic hydrogen/'' Mitchell J states that 

 ±Q$£> occurs in the flash spectrum, and reaches a level of 

 2000 kins. If the identification be all right, helium would 

 present a seemingly anomalous case, for, whereas other 

 elements are ionized in the upper strata, it is ionized in the 

 lower strata of the chromosphere.' 



The above sketch embodies, in short, the problems before 

 us. The alkaline earths and the heavier elements are 

 ionized throughout the whole of the solar atmosphere, but 

 the ionization is complete in the chromosphere, which seems 

 to contain no normal atom at all. But hydrogen and helium 

 are probably unionized throughout the whole chromosphere, 

 and in the case of helium we have probably some slight 

 ionization in the lower parts — a rather anomalous case. 



The explanation of these problems, and some other asso- 

 ciated problems of solar physics, will be attempted in this 

 paper. The method is based upon a recent work of 



* Kossel and Sommerfeld, loc. cit. p. 2.50. 

 r This line ia masked bv the strong- hydrogen line 11/- 

 I Mitchell, loc. cit pp. 490-491. 

 2 12 



