xxviii GENERAL SUMMARY OF SCIENTIFIC AND 



Of these, No. III. was the only bright one, and was, indeed, 

 the brightest of all that have visited the solar system since 

 1861; further details concerning it will be given below in a 

 subsequent section. 



Notwithstanding the unfavorable weather of the early 

 spring, Professor Newcomb has been able to secure with the 

 Washington refractor a very complete series of observations 

 of the four satellites of Uranus, the total number of deter- 

 minations of position exceeding that of all previous astrono- 

 mers combined. The satellites of Neptune have also been 

 carefully observed with this instrument. The reflecting pow- 

 er of Mercury has been investigated by Zollner, by means 

 of his elegant photometer. Messrs. Vogel, Lohse, and Klein 

 adduce arguments supporting the view that there may exist 

 a satellite to the planet Venus. 



As the accuracy of all astronomical deductions depends 

 more or less upon the perfect regularity of the diurnal rota- 

 tion of the earth, special importance attaches to the conclu- 

 sion of Professor Newcomb that certain irregularities may 

 exist in that motion, affording us the most probable explana- 

 tion of phenomena observed in connection with the motions 

 of both our own and Jupiter's moons. 



The Zodiacal Light. The zodiacal light has been the sub- 

 ject of very careful observation by Wright, of Yale College, 

 who concludes from the polarization of its light that it must 

 be a ring of small bodies attending the sun : a view that is 

 also compatible with the theories of Jones, Alexander, and 

 others, while Groneman goes still further, and argues very 

 plausibly that the aurora, the zodiacal light, and the meteoric 

 bodies have this in common, namely, that they are one and 

 all portions of that cosmical dust that pervades all the solar 

 system, and is rendered visible by either the reflected light 

 of the sun, the heat produced by friction, or by electric dis- 

 charges. 



Comets. Among the numerous investigations called out 

 by the appearance of Coggia's comet, we note briefly the 

 careful observations of the extent of its tail by Heis and 

 Abbe, the elaborate theory of the structure, nature, and origin 

 of the tail by Faye, who seems, however, merely to have elab- 

 orated the views relative to a repulsive force presented by 

 Professor Peirce, and by G. W. Bond in his incomparable 



