1881.] 



President 's Address. 



63 



may be mentioned that on Professor Pickering's initiative a committee 

 of American astronomers has been formed to co-operate with European 

 astronomers in selecting a series of stars to serve as standards of 

 stellar magnitude. 



The present year has been remarkable for the appearance of two 

 bright comets simultaneously visible to the naked eye. The first comet 

 was first seen in the southern hemisphere before its perihelion passage, 

 and burst upon our view in its full splendour soon after perihelion. 

 The most important point in connexion with this comet was that 

 photographs of its spectrum were obtained by Dr. Huggins and 

 Dr. Draper. The former found on his photographs two strong 

 bright lines in the ultra-violet corresponding to a group in the 

 spectra of compounds of carbon, and also a group of lines between Gr- 

 and h agreeing in position with another carbon-band. The photo- 

 graphs also showed a continuous spectrum extending from F to some 

 distance beyond H, on which the dark Fraunhofer lines were seen — 

 an indication that part of the light from comets is reflected solar 

 light. 



In the visible portion, the continuous spectrum was so bright when 

 the comet was first seen after perihelion that it almost obliterated the 

 ordinary cometary bands. These, however, became afterwards very 

 conspicuous, and five bands were noted, which were found to coincide 

 sensibly with the carbon-bands as given by the flame of the Bunsen 

 burner. On the brightest band, three bright lines corresponding to three 

 lines in the carbon-band were seen by several observers at Princeton, 

 U.S. These observations show conclusively that the spectrum of 

 this comet is identical with the first spectrum of carbon, and not with 

 the second. 



In the telescope this comet showed striking changes from day to 

 day, and even, according to some observers, from hour to hour, and the 

 head was remarkable for its unsymmetrical appearance. Another point 

 of interest is that the orbit presents a remarkable resemblance to that of 

 the great comet of 1807. As, however, the period of this latter was 

 found by Bessel to be 1540 years, the question arises again, as in the 

 case of the comets of 1843 and 1880, whether there are not two 

 comets travelling along the same path. 



The second bright comet was first discovered with the telescope, and 

 gradually increased in brightness till it became visible to the naked 

 eye, though by no means so interesting an object as the preceding 

 comet. Besides these two bright comets, several telescopic comets 

 have been discovered, raising the total for this year to eight. The 

 last but one of these has proved to be a periodic comet, revolving in the 

 short period of about eight years. It was discovered by an English- 

 man, Mr. Denning, being the first instance of such a discovery in this 

 country for many years. 



