74 



KNOWLEDGE. 



[April 1, 1901. 



were a little more fortunate, and noted that on the 22nd, 

 at 6.58. G.M.T., the star was about 0.3 mag. brighter 

 than a. Tauri, and at 8.10 p.m. equal to Procyou, while 

 on the 23rd, at 8.10 p.m., the nova exceeded Capella 

 by 0.2 mag. On the 25th, observations at 6.30 p.m. at 

 Kensington showed the nova to be intermediate between 

 Aldebaran and Capella, but by midnight the star had 

 perceptibly dimmed. By the 28th of February, the 

 star had dwindled to about 2nd magnitude. Observations 

 made by Colonel Maikwick and others also indicate that 

 the greatest brightness, near magnitude — 0.3, was 

 reached about the 23rd of February. 



Continued observations of the brightness of the star 

 will be of great interest, and to those making estimates 

 the following list of the magnitudes (Oxford Photometry) 

 of the stars shown in Fig. 2 may be useful : — 



The latest observation to which reference can be made 

 in the present article was made on March 12, when the 

 magnitude of the nova was estimated to be about 4.0. 



The colour of the new star has also been changing. 

 At the time of discovery. Dr. Anderson considered it to 

 be bluish white, but a gradually increasing redness 

 appears to have set in about the 25tli of February, and by 

 March 2nd the star was distinctly of a red tinge to the 

 naked eye. 



It is undoubtedly to the spectroscopic observations 

 that we must look for the greatest additions to our 

 knowledge of these strange outbursts, and it is satis- 

 factory to know that excellent records of the spectrum 

 have been secured. The earliest of these observations 

 was made on February 22nd by Dr. Copeland, who 

 found that the spectrum was then a continuous one 

 crossed by a few dark lines, and described it as of a 

 feebly developed solar type. At Harvard the spectrum 

 was photographed on the 22nd, a few hours after Dr. 

 Copeland's observations, and it was stated that 

 the negatives showed 25 dark lines, six of them with 

 bright lines on their less refrangible sides, and one with 

 a bright line on the violet side. 



In a communication to the Royal Society on February 

 the twenty-eighth. Sir Norman Lockyer stated 

 that 10 photographs had been obtained at Kensington 

 on February 25th, and it was remarked that the spec- 

 trum of the latest nova was strikingly similar to that 

 of Nova Auriga? (1892). Brilliant lines of hydro- 

 gen at C and F, three strong bright lines in the green, 

 and one in the yellow, each accompanied by a dark 

 line on the violet side were obvious in a glance at the 

 spectrum. The photographs showed similar pairs of dark 

 and bright lines in other members of the hydrogen 

 series, as well as in the K line of calcium, in addition 

 to numerous other dark and bright bands. All the 

 lines were very wide, and the separation of the bright 

 and dark adjacent lines indicated a relative velocity 

 of the two light sources of at least 700 miles per second, 

 assuming that the displacement of the dark lines was due 

 to motion in the line of sight. Some of the bright 

 lines were apparently reversed — that is, there was a 

 dark line down their centres. The velocities of the two 



light sources indicated by the spectrum were determined 

 by photographing the spectrum of y Orionis side by side 

 with that of the nova ; this disclosed the fact that the 

 bright line source, apart from internal movements, was 

 almost at rest with regard to the earth, while that 

 giving dark lines was approaching the earth with the 

 tremendous velocity already stated. 



The spectrum is by no means easy to unravel, 

 owing to the great breadth of the lines, both bright 

 and dark. Spaces between bright lines may easily 

 be mistaken for dark bands, and vice verso. Never- 

 theless, starting with the supposition that as some 

 of the lines are not unfamiliar, most of them may be met 

 with in other stars, it seems possible that the true dark 

 lines may be discriminated by a process of matching 

 with stellar spectra. In this way Sir Norman Lockyer 

 has concluded that the dark line spectrum of Feb- 

 ruary 25th was very similar to that which the spectrum 

 of a Cygni would assume if all its lines were to become 

 greatly distended through violent internal motions or 

 other causes. If this be a correct interpretation, the 

 spectrum then consisted largely of the enhanced lines* of 

 various metals, and a temperature considerably greater 

 than that of the sun or Sirius was indicated at this stage 

 in the history of the new star. The relation between the 

 spectrum of Nova Aurigfe and that of the solar chromo- 

 sphere to which attention was drawn by A^ogel and 

 others thijs appears to have depended upon the presence 

 of enhanced lines in" each. 



In another communication to the Royal Society on 

 March the seventh, Sir Norman Lockyer gave an 

 account of photographs taken on February 28, and March 

 1, 3, and 5, from which it ai^pears that considerable 

 changes in the spectrum were taking place. The con- 

 tinuous spectrum and bright lines other than those of 

 hydrogen were rapidly fading; the bright hydrogen 

 lines became very complex and were possibly quad- 

 ruple ; and some of the dark lines were dying out 

 while new ones appeared. Careful examination of the 

 photographs left little doubt that the principal bright 

 lines in the green, near wave lengths 4924, 5018, and 

 5169, and a less bright one at 5317, were due to iron 

 vapour at a very high temperature, while many others 

 in the more refrangible parts of the spectrum also corre- 

 sponded with high temperature metallic lines. Helium 

 lines appeared to be absent, and the line in the yelJow 

 was probably D and not 1)^. 



During this period a great part of the light of the 

 star was due to glowing hydrogen, and the star was, 

 therefore, red for the same reason that many of the solar 

 prominences are red. 



Excellent photographs of the sipectrum have also 

 been obtained by Father Sidgreaves, Mr. Newall, and 

 Dr. McClean; these exhibit the features described 

 above, and Dr. McClean finds many coincidences between 

 lines of the nova and those of Sirius, as would be ex- 

 pected, since the latter include numerous enhanced lines. 

 M. Deslandres has also given a good account of the 

 photographic spectrum (Coniptex Rendiix, March 4). 



A further description of the photograph taken at 

 Harvard on the 22nd of February, and details of others 

 obtained on the 23rd, 24th, and 25th. have been received 



* Enhanced lines are -those which are brightened in the spark 

 spectrum as compared witli the arc spectrum, and since these lines 

 occur without the arc lines in the spectra of some stars, whicli there is 

 reason to believe to be at a very high temperature, they are regarded 

 by Sir Norman Lockyer as indicative of high temperature when they 

 are met with in other spectrii. 



