THE GREAT COMET OF 1882. 295 



great equatorial was very much what it had been on the 10th with 

 the smaller telescope. There were no envelopes, and the only "jet" 

 was the bright streak following the nucleus. The dark stripe had 

 wholly disappeared, as if obliterated and replaced by the bright one. 

 The " knots " in the nucleus were seen to be irregular in form, and 

 were arranged not in a straight line, but in a somewhat broken curve, 

 conforming to the curvature of the tail, which at this time extended 

 18, and was fully 60,000,000 miles in length. The bright stream 

 originated not at the extremity of the nucleus, but came out tangen- 

 tially from the convex side, and perhaps had its source in the largest of 

 the knots, which was now the third from the sunward extremity. The 

 whole length of the nucleus measured 48^", corresponding to a length 

 of more than 40,000 miles, the diameter of the largest single mass 

 being about 5,000 or 6,000 miles. The only other observation we 

 have been able to make at Princeton was nine days later, on October 

 24th. No material changes were noticed, though the comet was very 

 much fainter. The same lengthened granular nucleus continued, and 

 seems likely to persist until the comet disappears.* 



The spectroscopic observations have been very interesting. On 

 September 18th the French physicist Thollon was an independent dis- 

 coverer of the comet, coming upon it accidentally in sweeping around 

 the sun. His spectroscopic apparatus consists of a so-called siderostat, 

 the mirror of which throws the rays from the object to be examined 

 upon the lens of a horizontal telescope nine and a half inches in diam- 

 eter and about twenty feet long. At the focus of this telescope in 

 a darkened room is placed a spectroscope, and, of course, this may be 

 of any form and power best suited to the occasion. In the present 

 case he used an instrument with a single prism of high dispersive 

 power. The most marked feature of the spectrum was the presence 

 of the lines of sodium in the spectrum of the nucleus. They were 

 very bright, and were displaced toward the red by an amount equal to 

 about one fourth of the interval between them, thus indicating that 

 the comet was rapidly receding from the earth. A very narrow, 

 bright, continuous spectrum was also shown by the nucleus. In this 

 the dark lines of Fraunhofer were not conspicuous if visible at all, 



* Later observations, on November 4th, show the same general characteristics. The 

 nucleus, if it can be so called, was now 93" in length, or more than 90,000 miles. Three 

 stellar points could be detected in the forward portion of the nucleus, but only two in 

 the other. The separation between the two brightest points was about 10". The spec- 

 trum showed no new developments. To the naked eye the comet was unexpectedly 

 bright, although now distant from both sun and earth nearly 140,000,000 miles. The 

 head looked like a fourth-magnitude star, and the tail was 16 long and 4 wide at the 

 extremity. On November 20th the nucleus had almost vanished, appearing merely as a 

 brighter streak in the structureless nebulosity of the head. The tail was still nearly as 

 large as ever, and easily visible without telescopic aid, though of course much fainter 

 than on the 4th. The comet has held out remarkably, and, so far as now appears, it may 

 be observable for a long time yet, especially in the southern hemisphere. 



