1880.] 



President 's Address. 



93 



Professor Pritchard, the result being to indicate the existence of a 

 small rotational inequality. 



Messrs. J. Campbell and Neison have made use of the Greenwich 

 Observations, 1862 to 1876, to determine the Lunar Parallactic 

 Inequality, from which they deduce for the value of the Solar 

 Parallax, 8"' 7 78, or 8 //- 848, according as the existence of a forty-five 

 year inequality, apparently indicated by the observations, is admitted 

 or not ("Monthly Notices," vol. xl, Nos. 7 and 8). The Sun's 

 Parallax has also been determined by Mr. Downing, from N.P.D. 

 observations of Mars at Leyden and Melbourne, in 1877. The value 

 thus found is 8" '96. (" Astronomische Nachrichten," No. 2,288.) 



In continuation of his researches on tidal retardation from the 

 action of a satellite on a viscous planet, Mr. G. H. Darwin has in- 

 vestigated the secular changes in the orbit of a satellite, deducing the 

 early history of the earth and moon from the time when they were 

 initially in contact, each revolving in the same period of from two to 

 four hours. This leads to the suggestion that the moon was produced 

 by the rupture of the primeval planet. In another memoir, Mr. G. H. 

 Darwin gives analytical expressions for the history of a planet and a 

 single satellite. ("Phil. Trans.," 1879, " Proc. Hoy. Soc," vol. 

 xxx, pp. 1, 255.) 



An important work in connexion with the United States Northern 

 Boundary Commission has been published by Mr. Lewis Boss, on the 

 Declination of Fixed Stars. The systematic corrections to some 

 seventy catalogues have been discussed, and, from the mean of the 

 whole, standard declinations of 500 stars have been deduced. 



Dr. Gould's " Uranometria Argentina " and M. Houzeau's " Ura- 

 nometrie Generale," are of especial value as giving important infor- 

 mation on the brightness and distribution of the stars in the southern 

 hemisphere. 



Interesting results as to the diameters of satellites have been ob- 

 tained by Professor Pickering from photometric observations, on the 

 assumption that their albedos do not differ greatly from those of 

 their respective primaries. (" Annals Harvard College Observatory," 

 vol. xi.) He has further investigated, on somewhat similar princi- 

 ples, the dimensions of the fixed stars, with especial reference to 

 binaries and variables of the Algol type. (" Proc. Amer. Acad.," 

 vol. xvi.) Professor Pickering has also commenced a photometric 

 survey of the heavens in which the brightness of every star visible to 

 the naked eye is to be determined. He has further undertaken a 

 search for planetary nebulae by a new method, in which, by the use 

 of a direct- vision prism in front of the eye-piece, the nebula is at once 

 detected by its monochromatic spectrum, focussing a point of light 

 instead of a coloured line as in the case of a star. About a hundred 

 thousand stars have been examined, and four new planetary nebulee 



