1904.] On the Temperature, Classification of Stars. 



235 



7. Discussion of Photographs. 



The following is a detailed discussion of the photographs described 

 in Table II. 



Stage 2 to Stage 4. 



No 19. This photograph of "Vega (fourth stage), and Arcturus (second 

 stage), is very striking in the relative intensities of the two spectra. 

 The red portion of the Arcturian spectrum is considerably more intense 

 and forms the one end of a maximum which — except in the green 

 region where the plate is not very sensitive — extends from D to about 

 A. 454. The part of the spectrum more refrangible than that rapidly 

 becomes less intense, until at and beyond K it is very faint. Matters 

 are very different in the spectrum of Vega. Here the maximum 

 radiation occurs about a third of the distance from Hs to H y (A. 422) 

 and the spectrum extends without any great falling off in intensity to 

 H„ , beyond that it is weaker but continues without any great decrease 

 to twice the distance on the more refrangible side of H v than the 

 latter is from K. From that point to the end the spectrum gradually 

 declines. Whilst the maximum radiation in this spectrum has moved 

 wholesale towards the ultra-violet, the red is relatively only about half 

 the density of the red in the Arcturian spectrum. 



No. 4. The general appearance of these two spectra leads to the 

 conclusion that that of /3 Ursse Ma j oris (fourth stage) is much stronger 

 than that of cc Ursse Majoris (second stage). 



A more careful examination, however, shows that whilst the 

 detached red part of the former is only seen with difficulty, the same 

 portion of the latter is comparatively prominent. 



The maximum intensity in cc is situated at about X 450 and does 

 not vary a great deal between there and K. After the latter point 

 is reached, however, the fall is rather sudden, and the spectrum soon 

 dies out. In f3 the maximum intensity is between H and H e5 and the 

 ultra-violet up to H K is fairly strong. Beyond H* the intensity of 

 the spectrum drops rather suddenly, and then continues with a gradual 

 decrease for some distance. 



No. 14. There is no great difference in the lengths of these two 

 spectra, the one of a Geminorum (fourth stage), the other cc Auriga? 

 (second stage), but the red portion of the second stage spectrum is 

 most decidedly more intense than that of the fourth^stage, the latter, 

 in fact, being scarcely visible at all. In cc Aurigse the maximum 

 intensity is at about X 454, but in cc Geminorum it must be placed at 

 or near to H§ (A. 410). 



No. 37. In the taking of this negative the spectrum of Capella 

 (second stage) received the advantage of exposure and is consequently 

 much stronger in the H Y — region than that of Castor (fourth 



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