RECENT ADVANCES IN SCIENCE 17 



and amongst other results clearly revealed a variation in the 

 period. This is discussed by Mr. Dugan in M.N., R.A.S. vol. 

 Ixxvi. p. 729, 19 16. 



" Determination of the Difference of Longitude between 

 Washington and Paris, 191 3-14," reduced by F. B. Little and 

 G. A. Hill : U.S. Naval Observatory, Washington, Publications, 

 Second Series, vol. ix. appendix, pp. 100, 1916. — This publica- 

 tion contains an account of the observations for the direct 

 determination by means of wireless telegraphy of the difference 

 of longitude between Washington and Paris, together with the 

 definitive reduction and discussion of the observations. 



11 Catalogue of Proper Motion Stars, Part II," by J. G. 

 Porter, Pub. of the Cincinnati Observatory, No. 18, pp. 113, 1916. 

 — Part I of this work, previously published, covered the 

 hours o h — 6 U right ascension ; the present publication continues 

 the results up to is h of right ascension. The observations 

 and their reduction are recorded in the same way as in the 

 previous part. The remaining part of the sky will subsequently 

 be published in Part III. The collection and calculation of a 

 large number of appreciable proper motions of stars in a large 

 area of the sky such as is contained in this work is of consider- 

 able importance for statistical discussions in astronomy. 



" Researches on the Proper Motions of Stars in the Helsing- 

 fors Photographic Zone : Part I, 9 to 12," by R. Furuhjelm, 

 Acta Societatis Scient. Fennica?, vol. xlviii. No. 1, pp. 190, 19 16. 

 — At the international astrographic congress of 1909, support 

 was given to the proposal that the astrographic zones should 

 be reobserved with a view to deriving proper motions from a 

 comparison of the plates taken at two epochs. The Helsingfors 

 zones were rephotographed from 1909 to 191 3, the original 

 photographs being obtained in 1892 to 1896. M. Furuhjelm 

 has compared corresponding plates in a stereocomparator and 

 has measured differentially the proper motions of all stars which 

 were revealed in this way to be in sensible motion. This 

 volume contains the results of the measurements from 9I1. to 

 I2h., 1,016 proper motions being derived. These results are 

 followed by a discussion of the accuracy of measurement and 

 of the distribution in magnitude and direction of the proper 

 motions. It is intended to complete the remaining hours in 

 the same way and then to discuss the whole of the material so 

 obtained. 



