o 



40 ANNUAL OF SCIENTIFIC DISCOVERY. 



closely the track which had been lain down for it, thus proving its 

 identit}^ with the objcet seen 11 years previously. It was ac- 

 cordingly removed from the ordinary class of parabolic comets, 

 and assigned an elliptic orbit with a period of 2031.55 days. An- 

 other return occurred in September, 18G2, but owing to unfavor- 

 able circumstances, similar to those that had operated in 1851, it 

 eluded detection. Bat early this year, faithful to prediction, it has 

 again appeared, passed its perihelion, and is now rapidly receding 

 from the sun. 



Father Secchi, of the College Observatory at Rome, who has 

 given much attention to spectroscopic research, has examined the 

 spectrum of this comet, and the results of his investigation are 

 given in a late number of the ' ' Comptes Rendus " (May 11) . From 

 the faintness of the object, the wliole liglit of the comet bein^ not 

 greater than that of a star of the seventh magnitude, which is in- 

 visible to the naked eye, the observations were attended with con- 

 siderable difficulty. 



We shall translate the most interesting portion of Secchi's com- 

 munication : — 



" The spectrum of the comet is discontinous ; it consists first of 

 a feeble light filling the field of view, is superposed by three bands 

 so vivid as to appear more dilated than the rest of the field. The 

 brightest of these bands is the middle one, which is in the green, 

 and corresponds to the region between the magnesium (b) and 

 the hydrogen (F), but much nearer the former; the breadth of 

 this band is very small, not greater than one-fifth of the dis- 

 tance between the two rays. At moments when the atmosphere 

 is particularly favorable it is reduced to a bright line of the same 

 apparent breadth as the nucleus of the comet. Another bright 

 band, but of much less intensity, is in the green-yellow, between 

 and equidistant from the sodium (D) and the magnesium (6). 

 Another band, in the red, may sometimes be distinguished, but 

 its position can be fixed only with the greatest difficulty. The 

 third luminous zone, nearly intermediate between the two preced- 

 ing, is near the blue end, about a third of the /listance between 

 F and G from F. This band is bright enough to admit of good 

 measurement, and to produce by scintillation the linear appear- 

 ance, 



" Tiiese observations lead us at once to results of considerable in- 

 terest. It seems first a justifiable inference that this comet shines 

 not merely by reflected solar light ; the only solar light is perhaps 

 that diffused in the field of view. The comet is, then, self-lumi- 

 nous, and its light is ver}^ like in color that of the nebulas, but very 

 different in position from that of the nebulous rays, of which one 

 coincides with f; the other ray of the comet is also in a different 

 position and at the opposite end, much nearer the magnesium than 

 the nebulous ray. It is thus proved that the displacement is not 

 caused by motion, but by the nature of cometary matter. More- 

 over, these bands being brighter than those of a star of equal 

 brilliancy, we are led to conclude that the comet emits light of its 

 own. The measures are not sufficiently precise to afford means 

 of rigorous comparison with other known spectra, and besides we 



