ASTRONOMY. 193 



shown that the variations in a Ursse are no greater than in the case of 

 these three stars, which are pretty certainly constant in color, and he 

 gives it as his opinion that a Urste must be considered also as of a con- 

 stant color, unless we are willing to admit that all stars are variable in 

 tint in short periods of time. This result is of more importance than at 

 first sight appears, as we have now no well authenticated case of varia- 

 tion of color separate from variation in brilliance. 



Dr. Gylden, of Stockholm, has recently published a mathematical 

 investigation, in which he shows the possibility of explaining the ob- 

 served variation in the light of stars upon pure mechanical principles. 

 He takes, as a basis the idea that the surfaces of such stars are covered 

 in parts with a kind of crust or slag^ which gives out less light tlian the 

 remaining i^arts of the surface, which are glowing. Further, he sup- 

 poses these stars to be rotating on their axes, and he shows that such a 

 rotation will account for all the phenomena, particularly as the axis of 

 rotation will itself be changed from time to time by the different dispo- 

 sition of the floating masses on the surface. It is noteworthy that the 

 possibility of such an explanation was first suggested by Sir William 

 Heechel. 



THE SUN. 



A new determination of the inclination of the ecliptic is contained in 

 the doctor- dissertation by B. F. van de Sandb Bakhuyzen, of the 

 Leiden Observatory. The author discusses the declinations of the sun 

 observed in Leiden in the years lSG4-'76, and enters into all details re- 

 hiting to the instrument used, etc. He finds that the inclination for 

 1870 as given in Leverrier's tables should be diminished by about 

 0".30. This result agrees well with Oppolzer's inclination for 1815 

 brought down to 1870, with a secular diminution as found by means of 

 the latest values of the planetary masses. 



A review of the new or modified theory of the constitution of the 

 sun, proposed by Dr. Hastings, is necessarily postponed for want of 

 the necessary space to detail his arguments. It may be briefly said, 

 however, that no theory of the s^^n's constitution previously proposed can 

 account for all the facts of both spectroscopic and telescopic observation ; 

 and it is claimed by Dr. Hastings with good show of reason that his 

 hypothesis does this satisfactorily. It was published in the Aiuerican 

 Journal of Science, and will doubtless receive the consideration asked 

 for it. 



Sun parallax. — Several determinations of the solar i^arallax have been 

 lately published. From his observations of Mars, made at Ascension 

 Island in 1877, Mr. Gill finds - = 8".78 (M.N. June, 1879). At the same 

 opposition Mr. Maxwell Hall, in Jamaica, made similar observations 

 of the displacement of Mars in E. A. (Mem. E. A. S., XLIV.) He used 

 an equatorial of four inches ajjerture. Mr. Hall has carefully reduced 

 S. Mis. 31 13 



