On 7] Arg'As and Nebula. 107 



seems to shew that small periodical fluctuations of its light 

 are still in progress, presaging possibly another outburst of 

 this wondrous variable. 



Mr. Le Sueur's first glance through the great Telescope 

 at 7] Argus, in April 1869, revealed important changes, shewn 

 in sketch 1 ; 77, which in 1838 was involved in dense nebula, 

 was seen on bare sky — the nebula having disappeared for 

 some distance around it — and the southern loop of the lemnis- 

 cate, consisting of equally dense nebula in 18-38, had grown 

 so faint as almost to disappear. The preceding side of the 

 lemniscate had bulged out into the vacuity and stretched 

 itself out into a bridge or isthmus, which, after a bend 

 towards a projecting cape on the other side which seemed to 

 stretch into the vacuity to meet it, passed northwards and 

 joined "the other loop of the lemniscate. The overlying 

 streak or veil alluded to by Herschel, and shewn in his 

 chart, had divided into a Y shaped appendage to the N end 

 of the iVp loop of the lemniscate, and in July following, 

 Mr. Le S. notes that a faint bridge existed, joining the S 

 end of the isthmus with the nebula on the / side, across the 

 vacuous channel. 



As -q Argus has no sensible parallax, and in all probability 

 is in physical connection with the nebula, we may assume 

 every second of arc upon the rough drawings supplied, to 

 represent at the least twice the diameter of the earth's orbit, 

 and as each of the sides of the squares shown upon the 

 drawings represents 180 seconds of arc, a rough scale is 

 supplied by which to estimate changes whose magnitude and 

 rapidity have no parallel in astronomic record ; yet these 

 changes as they are followed through their cycle, may 

 remind the observer more or less forcibly of internal changes 

 not very dissimilar, which are so frequently exhibited in 

 sun-spots. 



Still more wonderful in its rapidity appears the change 

 represented by Mr. Le S's next drawing of January 1870, 

 only six months later, readily shewn in sketch 2. The 

 isthmus of nebula has detached itself from the north side of 

 the lemniscate, and withdrawn itself through 90 seconds of 

 arc to form a broader peninsula of nebula, with such 

 rapidity, that the severed end of the isthmus would appear 

 to have travelled at a rate, per month, of 30 times the 

 diameter of our orbit. These distances are of course esti- 

 mated at right angles with the visual ray, and the real 

 distances will in all cases be greater, since the various parts 



