1892.] on the New Star in Auriga. 619 



the plate, but the Dext night that was clear, December 10th, the 

 Nova is recorded as of the fifth magnitude. Most fortunately, on 

 December 8, Dr. Max Wolf photographed this part of the constella- 

 tion of Auriga, but no star so bright as of the ninth magnitude was to 

 be found where the Nova afterwards appeared. 



The new star must therefore have sprung up to the brightness of 

 the fifth magnitude between the 8th and the 10 th of December last. 



At that early time the Nova was not nebulous on Prof. Pickering's 

 plates. The question has been raised since whether the star was 

 surrounded by a faint nebula. To us, in our observations, it appeared 

 like an ordinary star ; but the point may be considered set at rest 

 by photographs taken by Mr. Roberts, which by his kindness I am 

 able to throw upon the screen. With an exposure of over three 

 hours, there is only the usual small fringe of nebulosity due to our 

 atmosphere, and which is present also about the other stars on the 

 plate. How searching a test for faint nebulous matter is so long an 

 exposure, is strikingly shown by contrasting a short exposure plate 

 of the Pleiades, where nebula do exist, with a photograph on which 

 the light action has been prolonged for nearly four hours. The 

 Nova is free from nebulosity in photographs which have been sent to 

 me by the Brothers Henry, and by Prof. Holden of the liick 

 Observatory. 



The changes of magnitude of the Nova as shown by photographs 

 taken at Greenwich, from eye-observations at Prof. Pritchard's ob- 

 servatory, and by Mr. Stone and by Mr. Knott, are recorded in the 

 diagram on the wall. These observations show that notwithstanding 

 continual fluctuations a slow but steady decline had set in, carrying 

 the light of the star from nearly the fourth and one-half magnitude 

 down to the sixth magnitude by the early days of March ; but after 

 March 7th, these swayings to and fro of its light, set up probably by 

 commotions attendant on the causes of the star's outburst, calmed down, 

 and the light fell rapidly and with regularity to about the eleventh 

 magnitude by March 24th, and then down to 14 • 5th magnitude by 

 April 1st. On April 26th, however, it was still visible at Harvard 

 observatory as a star of the 14* 5th magnitude. 



We commenced our observations on February 2nd. The spectrum 

 of the star in the visible region is represented in Fig. 1 of Plate II. 

 Below the star's spectrum are placed the terrestrial sjDectra with 

 which it was directly compared. The spectrum showed a brilliant 

 array of bright lines, among which four in the green were very 

 conspicuous. 



The brightest of these we recognised as the second line of hydro- 

 gen, and passing the eye to the red, we saw blazing the first line of 

 hydrogen at C ; the blue line near G was also visible. But a remark- 

 able phenomenon presented itself in that each bright line seemed to 

 cast a shadow, for on the blue side of each was a narrow space of 

 intense blackness. When we threw into the spectroscope for com- 

 parison the bright lines of hydrogen, the secret of this unusual 



2 T 2 



