104 BARNARD— SOME PECULIARITIES OF THE NOV^. 



magnitude. As I have stated, no other nova is known to have shovi^n 

 this second bright maximum. 



Some of the novae present very beautiful phenomena, especially 

 in the wonderful colors they sometimes exhibit in their declining 

 phases. At first these stars seem to be white ; very soon they become 

 red and pass through various colors, finally ending in a more or less 

 colorless condition, their faintness preventing any appearance of color 

 in them, if it existed. Their most beautiful colors, however, are 

 seen in the telescope, usually after they have ceased to be visible to 

 the naked eye — if they have been so bright as that. I would speak 

 specially of two of these stars of recent years which have shown the 

 most beautiful colors. 



In March of 1919 Nova Aquilse, in the telescope, was the most 

 exquisite and intense blue, a color that no other star in the heavens 

 could match. In September, 1920, Denning's Nova Cygni was a 

 most remarkable object in a large telescope. At the ordinary focus 

 was a white or nearly white stellar image surrounded by a brilliant 

 system of crimson rays. At 9 mm. outside the focus the image was 

 very small and beautifully scarlet. It was surrounded by splendid 

 blue and golden rays. In one position of focus there was no central 

 image, but a system of rays radiating from the center. For the first 

 half of their length these rays were golden, while their outer half was 

 crimson. The crimson color was due to the a Hydrogen line which 

 was then specially strong in the spectrum of the star and gave a 

 beautiful scarlet stellar image 9 mm. outside the normal focus. 



The two great novae of recent years, Nova Persei and Nova 

 Aquife, have shown in their declining phase a remarkable phenom- 

 enon — that of a measurable planetary disc instead of the stellar point 

 which all stars exhibit. In the case of Nova Aquilae this measurable 

 disc lasted for at least two months and seemed to be gradually in- 

 creasing in size. On October 5, 1918. its measured diameter was 

 o".8, while on December 14 it was i".8. The disc was sharply 

 defined and its light was dull and planetary. Later the star resumed 

 the regular stellar image. Aitken, in August and September of 1919, 

 found, with the 36-inch telescope of the Lick Observatory, that with 

 the telescope set for the focus of the nebulium lines N^ and N,, 8 mm. 

 outside the normal focus, there was a definite disc 2". 4 in diameter. 



