ZONE OF PLANETS BETWEEN MAES AND JUPITEE. 67 



nitude in a position where none had been visible before, 

 and noted it down for re-examination. On the following 

 evening this object was found to have retrograded one 

 minute, thus leaving no doubt of its planetary nature. 

 On the 27th the discovery was announced to several as- 

 tronomers in England and on the Continent, and soon 

 became generally known through the circulars issued by 

 Professor Schumacher. The name selected for this planet 

 is Metis, with an eye and star for a symbol. This planet 

 is remarkable for the near coincidence of its mean motion 

 with that of Iris, the duTerence of their periodic times, 

 according to the most recent calculations, amounting to 

 less than one day. 



On the 12th of April, 1849, Dr. Annibal de Gasparis, 

 assistant astronomer at the royal observatory at Naples, 

 while comparing the Berlin chart for the twelfth hour 

 of right ascension with* the heavens, perceived a star of 

 between the ninth and tenth magnitudes, in a position 

 which he had found vacant at previous examinations of 

 this region. Unfavorable weather interrupted his ob- 

 servations for that evening, but on the 14th he ascer- 

 tained that it had sensibly changed its place, and was 

 therefore a new planet. Professor Capocci, director of 

 the Neapolitan observatory, named the planet Hygeia. 

 The mean distance of this planet from the sun is, with 

 perhaps a single exception, greater than that of any other 

 known member of this group, corresponding to a revolu- 

 tion in 2041 days. 



On the occasion of the discovery of Hygeia, Sir John 



