in the Solar Chromosphei 



487 



Taking V 2 = 20*5 volts, U=-4'8xl0 5 calories approxi- 

 mately, we have the following table for the first step 

 ionization of parhelium. If the ionization voltage be taken 

 = 25 volts, the degree of dissociation will become still 

 less:— 



Table IX. 



Ionization of Helium (in per cents.). 



U = 4*8 . 10 5 calories (approximately). 



1. 



5.10 _(5 

 1.10- 4 

 4.10-* 

 1-2. 10- 3 

 7.10- 3 



Pressure 



Temp. 



6000 ... 



7000 ... 



7500 ... 



8000 ... 



9000 ... 



10000 3.10 -2 



11000 1.10 -1 



12000 3-10 -1 



13000 7.10 -1 



14000 1-5 



15000 3 



16000 6 



10~ J 



1-7.10 



3-6.10 



1-2.10 



3-7.10 



2-3.10 



1.10 



3-4.10 



1 



2 



4 

 10 

 17 



—3 

 3 



10- 1 



5.10 

 1.10 



4.10 - 



1-2. 10" 2 



7 . 10~ 2 



3.10 -1 



1 



3 



7 



15 



28 



47 



io- 5 - 



1-7. 10 -4 

 3-6. 10~ 3 

 1-2. IO" 2 

 3-7. IO" 2 

 2-3.10 -1 

 1 



3-4 



10 



22 



43 



68 



85 



10 '\ 



5.10" 4 

 1 . IO" 2 



1-2. IO" 1 



7.10- 1 

 3 

 11 

 28 

 58 

 83 

 94 



10~ b . 



5.10 _:3 

 1.10" 1 



3-7. IO -1 



7 

 31 

 72 

 93 



The table shows clearly the ionization of helium is too 

 slight under the conditions in the solar atmosphere, both in 

 the reversing layer (T 7500, pressure = 1 atm.), as well as in 

 the high-level chromosphere (T = 6000°, /> = 10~ 6 atmos.) 

 But somewhere between the two (T 7000°, y> = 10~ 3 atm.), 

 there may be some slight ionization (1 in 10,000) which 

 may account for the occurrence of the line of ionized helium 

 A, = 4686, which has been detected by Mitchell. The 

 calculations are, of course, of the roughest nature. 



The investigation also incidentally shows that the Pickering 



lines i/ = 1S[ ^ — 7— — r^ and the Rydbero- line 4686 can 

 \_1- (ra-f£)J J & 



occur as absorption-lines only in stars having the highest 

 temperature, exceeding 16,000° K. This seems to be in- 

 dependently borne out by the investigations of Eddington 

 and Russell. 



The application of the method and the results obtained in 

 the present paper to the problems of temperature radiation 

 of elements and of the different spectral types of stars 

 naturally suggest themselves, and will be taken up in a 

 future communication. 



