013 -Mr. William Huggins [May 13, 



If the plane of the star-system is inclined to the line of sight, the 

 dark body might pass above or below the bright one as seen from 

 the earth, and not eclipse it. Vogel had the good fortune to discover 

 such a system in Spica, which he showed to consist of a pair of great 

 suns, one bright and the other dark, or nearly so, whirling round 

 their common centre of gravity in about four days. 



If, however, in a binary system both stars are bright, the minute 

 stellar point formed in the telescope will contain the light of both 

 stars ; and its spectrum will be a compound one, the spectrum of one 

 bright star being superposed upon that of the other. If the spectra 

 are identical, all the lines will be really double, though apparently 

 single when the stars have no relative motion ; and will open and 

 close in periods depending upon the stars' motions. 



Such a system was first made known to us spectroscopically by 

 Prof. Pickering from his photographs of Mizar, which consists of a 

 pair of gigantic blazing suns, equal together to forty times the sun's 

 mass and whirling round their common centre of gravity with the 

 speed of about 50 miles a second. Then followed at Harvard the 

 discovery in (3 Auriga of an order of close binary stars hitherto un- 

 known. In Fig. 2 of Plate I. are reproduced the original photographs 

 showing the duplication every second day of the lines in the spectra 

 of this double star ; the doubling is well seen in K, which is very 

 narrow in this star. 



Now it is to this method of spectroscopic observation that we are 

 indebted for the revelation of the remarkable state of things existing 

 in the new star. I may remark, in passing, that it is not a little sur- 

 prising that a new star as bright as the fifth magnitude should have 

 burst out almost directly overhead in the heavens, and yet have 

 remained undiscovered for nearly seven weeks. Europe and the 

 United States bristle every clear night with telescopes pointed from 

 open observatories, which are served by an army of astronomers ; 

 and yet the honour of the discovery of the new star is due to an 

 amateur Mr. Anderson, possessed only of a small pocket-telescope 

 and a star-chart. Happily the days are not over when discoveries 

 can be made without an armoury of instruments. ^ ^ ^ .^. , . 



As soon as the news reached Cambridge, U.S., Prof. Pickering, 

 by means of photographs which had been taken there, was able to 

 cause the part of the sky where the new star appeared, to pass again 

 under his examination, precisely as it had appeared at successive 

 intervals during the last six years ; but the new star's place had 

 remained unoccupied all that time by any star so bright as of the 



eleventh magnitude. ^ , , , ^ ^i, i 



For about a year a still closer watch has been kept upon the sky 

 at Cambridge by means of a photographic transit instrument driven 

 by clockwork, which automatically patrols the sky every clear night, 

 and retristers upon one plate all stars as bright as of the sixth mag- 

 nitude °within a great zone 60^ in breadth, and three hours of Eight 

 \sceusion in length. On December 1 the Nova did not appear upon 



