300 SCIENTIFIC RECORD FOR 1882. 



diameter of the nucleus as about 15". This spectrum stretched very 

 far into the violet. The bright lines of sodium T>i and D2 were given 

 at the same time both by the nucleus and by the neighboring regions- 

 From their length we estimated the apparent diameter of the part of 

 the comet which displayed them at l.'o. • They were neither diffused 

 iLor broadened, but narrow and perfectly separated, and exceedingly 

 bright, especially in the spectrum of the nucleus. They were nearly of 

 the same brilliancy, however, the most refrangible seemed a little the 

 brighter, and they were, in short, exactly like the lines given by a flame 

 moderately charged with sodium, both in brightness and in their essen- 

 tial charaxjteristics. Of their identity there can be doubt, for besides 

 the characteristics which we have just pointed out, we compared their 

 positions with those of the Fraunhofer lines Di and D2, given by the spec- 

 trum of the diffused daylight. We ascertained that the bright lines of 

 the comet were not exactly superposed on the Fraunhofer lines, but 

 were both displaced towards the red by a very small amount, the same 

 in each case, equal perhaps to J or 1 of the interval between D; and D>. 

 We therefore concluded that the comet was traveling away from the 

 earth at that moment. We intended to measure this displacement the 

 next day, and prepared a more powerful spectroscope for this purijose; 

 but the state of the sky did not give us the opportuuity. No part of 

 the comet showed us the bands of carbon, nor any band or line other 

 than those of sodium, perhaps on account of the diffused light, which 

 would be able to mask bands of small brilliancy. 



"The singular analogy between the spectrum of this comet and that 

 of comet Wells, observed some months ago, will doubtless aj^pear the 

 more remarkable, as preceding comets have never shown the lines of 

 sodium." 



But as the comet has receded from the sun, the ordinary cometary 

 hydrocarbon bands have made their appearance, and the ordinarj^ yel- 

 low, green, and blue bands had become very conspicuous on October 

 1, whilst the sodium lines were very much fainter. M. Ricco, at Palermo, 

 observing up to October 11, found the spectrum of the tail perfectly con- 

 tinuous, and could trace it right to the end. The three hydrocarbon 

 bands were only given by the nucleus and a region of some 5' radius 

 Bound it. 



These changes in the spectrum, as the comet recedes from perihelion, 

 combined with the reverse changes witnessed in that of comet Wells 

 as it approached it, seem to render it not unlikely that sodium would 

 appear in the spectrum of any comet which should approach the sun 

 sufficiently nearly; that it is, in fact, an indication of excessively high 

 temperature, as the hydrocarbon bands are of one not quite so great. An 

 intermediate spectrum of which no definite details have yet been sup- 

 plied seems to have been observed at Dun-Echt and elsewhere. M. 

 Eicco speaks of having seen many lines up to September 27, a band in 

 the red, a line iu the yellow near and after Di, two others in the greeo, 



