94 



Anniversary Meeting. 



[Nov. 30, 



have been detected. (" American Journal of Science," October, 

 1880.) 



From the grouping of the aphelia of certain periodic comets, Pro- 

 fessor Gr. Forbes has inferred the existence of two ultra- Neptunian 

 planets, and has indicated their approximate positions. (" Trans. 

 Roy. Soc, Edinburgh.") Mr. D. P. Todd has deduced from the per- 

 turbation of Uranus, a position for an ultra- Neptunian planet closely 

 agreeing with that found by Professor Gr. Forbes. So far, the search 

 for the hypothetical planet with the 26-inch Washington refractor has 

 been unsuccessful. ("American Journal of Science," September, 1880.) 



Professor Bredichin's researches on the tails of comets have led 

 him to the classification of these appendages according to the value 

 of the solar repulsive force wbich would have generated them. 

 Having discussed the forms of the tails of thirty-three comets, he 

 finds that they belong to three types, corresponding respectively to 

 repulsive forces 11, 1*4 and 0"3 (the sun's gravitation being taken 

 as 1), and adopting Zbllner's hypothesis of a repulsive force, due to 

 electricity and inversely proportional to the specific gravity, he infers 

 that the tails of the three types are composed respectively of 

 hydrogen, carbon, and iron. In the case of the second and third 

 types other elements of nearly the same atomic weight may replace or 

 be mixed with the carbon and iron, and in such a comet as Donati's 

 a number of substances may be mixed in the tail, which will con- 

 sequently spread out in the plane of the orbit. The first type com- 

 posed of hydrogen will always remain separated from the others. 

 (" Annales de l'Observatoire de Moscou," vols, iii — vi.) 



The appearance, at the beginning of this year, of a great comet in 

 the southern hemisphere, recalling by the length of its tail and the 

 smallness of its head the remarkable comet of 1843, has excited great 

 interest, more especially as it was found that the. orbits of the two 

 comets were sensibly the same. The observations of the comet of 

 1843, however, do not appear to be compatible with so short a period 

 as thirty-seven years, and Professor Oppolzer has shown that the 

 action of a resisting medium would not meet the case. (" Astro - 

 nomische Nachrichten,'' Nos. 2314, 2315.) Under these circum- 

 stances Professor D. Kirkwood has suggested that the two bodies may 

 be fragments of one original comet, viz., that of 370 B.C., which is 

 said to have separated into two parts like Biela's comet. (" Obser- 

 vatory," No. 43.) Five other comets (including Faye's periodical 

 comet) have been discovered this year, but two of them were lost 

 through cloudy weather before a second observation could be 

 made. 



In astronomical physics Mr. Huggins has obtained photographs of 

 stellar spectra, which establish the existence of a remarkable group of 

 nine bands in the ultra-violet, probably due to hydrogen, and farther 



