62 



Anniversary Meeting. 



[Nov. 30, 



institute observations at Fort Simpson, and that the Government of 

 France may organise a simultaneous meteorological expedition to 

 Terra del Fuego. It is arranged that the observations should begin 

 as soon as possible after August 1, 1881, and should continue to 

 September 1, 1883. 



In astronomy, Mr. Gill has completed his discussion of the exten- 

 sive series of heliometer measures of the parallax of Mars, which he 

 made at Ascension in 1877, and has deduced the value 8"' 78 for the 

 solar parallax, corresponding to a mean distance of 93,080,000 miles 

 from the earth to the sun. A value of the solar parallax has also 

 been derived by Mr. D. P. Todd, from the American photographs of 

 the transit of Venus, 1874. The result for the parallax is 8" "883, 

 corresponding to a mean distance of 92,028,000 miles. 



A valuable contribution towards the determination of the moon's 

 physical libration has been made by Dr. Hartwig. From a series of 

 42 measures made with the Strassburg heliometer he derives values 

 for the physical libration and for the inclination of the moon's axis, 

 substantially confirming the results found by Wichmann, and recently 

 by Professor Pritchard. 



An addition to the small list of stars which have been found to have 

 a measurable parallax, has been made by Dr. Ball. He finds that the 

 star Groombridge 1618, which is remarkable for its large proper 

 motion, has a parallax of about one-third of a second, so that it is to be 

 considered one of the sun's nearest neighbours. Dr. Ball has also re- 

 determined the parallax of the double star 61 Cygni, his result being 

 0"*468, which agrees more nearly with Struve's value than with 

 Bessel's. 



The Cape catalogue of upwards of 12,000 stars is the outcome of 

 Mr. Stone's labours during nine years, as Her Majesty's Astronomer 

 at the Cape, and is the most important catalogue of stars which has 

 yet been formed in the southern hemisphere. Another important con- 

 tribution to stellar astronomy has been made by Professor Newcomb, 

 who has recently prepared a catalogue of the places of nearly 1,100 

 standard stars compiled from the best authorities. 



In connexion with his photometric researches, Professor Pickering 

 has discussed the causes of the variability of stars of short period. 

 Taking the various hypotheses which have been proposed, he finds that 

 for Algol and stars of that type the hypothesis of an eclipsing satellite 

 or cloud of meteors revolving round the star is the only one which 

 satisfies the observed phenomena. In the case of /3 Lyras and similar 

 variables the fluctuations of light would be explained as due to rota- 

 tion round the axis, the two hemispheres being of unequal brightness 

 and the form more or less elongated. Professor Pickering has very 

 carefully investigated the conditions in each individual case, and has 

 brought together the most important facts bearing on the subject. It 



