232 



Sir Norman Lockyer. 



[Jan. 30, 



star as yet known representing the Argonian group is situated in the 

 Southern Hemisphere. The stages already investigated are shown by 

 brackets in the following table. 



10. 



9. 



8. Crucian. 



7. Taurian. 



6. Rigelian. 



5. Cygnian. 



4. 



3. Polarian. 



2. Aldebarian. 



1. Antarian. 



Argonian. 

 Alnitamian. 



Table I. 



Achernian. 



Algolian. 



Markabian. 



Sirian. 

 Procyonian. 

 Arcturian. 

 Piscian. 



6. 



Thus an Arcturian star (second stage), was compared with a Sirian 

 (fourth stage), and so on. In the case of some stars, e.g., Capella, 

 this was repeated several times, each photograph showing a different 

 comparison. 



In securing the photographs an attempt was always made to obtain 

 the pair of spectra with the region between and H y of the same 

 intensity in each. This condition is very difficult to fulfil in actual 

 practice owing to the difference of magnitude of the two stars, their 

 difference in declination, and hence in clock rate, and lastly the very 

 important actual differences between the actinism of the two bodies 

 in this region of the spectrum due to their different temperature 

 conditions. 



It was also arranged to obtain, whenever possible, the spectra of two 

 stars near together, so that the chances of introducing atmospheric 

 interference due to the different conditions possibly present in various 

 parts of the sky might be reduced to a minimum. In every case where 

 the observer had reason to suspect any change in the atmospheric 

 conditions obtaining during the two exposures, which sometimes 

 extended over a period of 1J hours, the result has not been included 

 in the discussion. 



Thus we have a series of comparison photographs from which all 

 variable conditions except the natural variations in radiation have, as 

 far as possible, been eliminated. 



