36 REPORT — 1891. 



the shore, or of particles of the wind-blown dust of the desert ? Surely 

 every star from Sirius and Vega down to each grain of the light-dust of 

 the Milky Way has its present place in the heavenly pattern from the 

 slow evolving of its past. We see a system of systems, for the broad 

 features of clusters and streams and spiral windings which mark the 

 general design are reproduced in every part. The whole is in motion, 

 each point shifting its position by miles every second, though from the 

 august magnitude of their distances from us and from each other, it is 

 only by the accumulated movements of years or of generations that some 

 small changes of relative position reveal themselves. 



The deciphering of this wonderfully intricate constitution of the 

 heavens will be undoubtedly one of the chief astronomical works of the 

 coming century. The primary task of the sun's motion in space together 

 with the motions of the brighter stars has been already put well within 

 our reach by the spectroscopic method of the measurement of star-motions 

 in the line of sight. 



From other directions information is accumnlating : from photographs 

 of clusters and parts of the Milky Way, by Roberts in this country, 

 Barnard at the Lick Observatory, and Russell at Sydney ; from the count- 

 ing of stars, and the detection of their configurations, by Holden and by 

 Backhouse ; from the mapping of the Milky Way by eye, at Parsonstown ; 

 from photographs of the spectra of stars, by Pickering at Harvard and in 

 Peru ; and from the exact portraiture of the heavens in the great interna- 

 tional star chart which begins this year. 



I have but touched some only of the problems of the newer side of 

 astronomy. Of the many others which would claim our attention if 

 time permitted I may name the following. The researches of the Earl of 

 Rosse on lunar radiation, and the work on the same subject and on the 

 sun, by Langley. Observations of lunar heat with an instrument of his 

 own invention by Mr. Boys ; and observations of the variation of the- 

 moon's heat with its phase by Mr. Frank Very. The discovery of the 

 nltra- violet part of the hydrogen spectrum, not in the laboratory, but from, 

 the stars. The confirmation of this spectrum by terrestrial hydrogen in 

 part by H. W. Vogel, and in its all but complete form by Cornu, who 

 found similar series in the ultra-violet spectra of aluminium and thallium. 

 The discovery of a simple formula for the hydrogen series by Balmer. The 

 important question as to the numerical spectral relationship of difierent- 

 substances, especially in connection with their chemical properties ; and 

 the further question as to the origin of the harmonic and other relation* 

 between the lines and the groupings of lines of spectra ; on these points 

 contributions during the past year have been made by Rudolf v. Kove- 

 sligethy, Ames, Hartley, Deslandres, Rydberg, Griinwald, Kayser and 

 Runge, Johnstone Stoney, and others. The remarkable employment of 

 interference phenomena by Professor Michelson for the determination of 

 the size, and distribution of light within them, of the images of objects 



