THE PRESIDENT'S ADDRESS. 319 



Observations of stellar spectra are now carried on system- 

 atically in several observatories in Europe and the United States, 

 especially at the Harvard Observatory, Cambridge, U.S., where 

 distinct researches are in progress with the object of making a 

 perfect catalogue of photographed spectra of all stars visible to 

 the naked eye. This catalogue is intended to be supplemented 

 by more elaborate photographs of the spectra of bright stars, 

 and also of some of the fainter stars. This great scientific re- 

 search is very near the point of completion. A few years ago 

 such an elaborate work would have been considered impracticable. 

 Some very successful photographs of the spectra of a few of the 

 brightest stars have been taken ; that of Sirius, for instance, 

 showing four hundred measurable lines. To obtain the spectra 

 of the principal stars in the southern hemisphere on the same 

 plan of observation, a special expedition has been sent to a 

 station 6000 feet above the level of the sea, near Chosica, Peru, 

 and already the spectra of about 1500 stars have been photo- 

 graphed, including a large number of interesting objects, of 

 which at least nine have the hydrogen line bright in their spectra* 

 indicating the presence of glowing gas. 



Another branch of spectroscopic research of considerable 

 scientific interest, has been introduced by Dr. Huggins, relating 

 to the determination of the motions of stars in the line of sight, 

 or the velocity of their approach towards, or their recession from 

 the earth, as observed by the visible displacements of certain 

 lines in the stellar spectra, when compared directly with corres- 

 ponding lines in the spectrum of hydrogen, or of any other 

 substance or gas. These observations have been made on the 

 theory that ' ' if the stars were moving towards or from the 

 earth, their motion compounded with the earth's motion, would 

 alter to an observer on the earth the refrangibility of the light 

 emitted by them, and consequently the lines of terrestrial sub- 

 stances would no longer coincide in position in the spectrum with 

 the dark lines produced by the absorption of the vapours of the 

 same substances in the stars."* 



Though it would not be in place for me to explain here the 

 scientific details of the various methods of observation employed 

 in this very important series of technical experiments, I think 



* Phil. Trans., 1868, p. 529. 



