1881.] Dr. Arlhiir Srintfifer on Modern Sj^edroscopy. 493 



WEEKLY EVENING MEETING, 



Friday, January 28, 1881. 



Thomas Boycott, Esq. M.D. F.L.S. Vicc-Presidcufc, in the Chair. 



Arthur Schuster, Esq. Ph D. F.R.S. 



The Teachings of Modern Spectroscopy. 



A sciENXE, like a child, grows quickest in the first few years of its 

 existence ; and it is therefore not astonishing that, though twenty years 

 only have ela2)sed since Spectrum Analysis first entered the world, we 

 are able to speak to-day of a modern spectroscopy, with higher and 

 more ambitious aims, striving to obtain results which shall surpass 

 in importance any of those achieved by the old spectroscopy, to the 

 astonishment of the scientific world. 



A few years ago the spectroscope was a chemical instrument. It 

 was the sole object of the spectroscopist to find out the nature of a 

 body by the examination of the light which that body sends out when 

 it is hot. The interest w^hich the new discovery created in scientific 

 and unscientific circles was due to the apparent victory over space 

 which it implied. No matter whether a body is placed in our labora- 

 tory or a thousand miles away — at the distance of the sun or of the 

 furthest star — as long as it is luminous and sufficiently hot, it gives 

 us a safe and certain indication of the elements it is composed of. 



To-day, we are no longer satisfied to know the chemical nature 

 of sun and stars ; we want to know their temperature, the pressure on 

 their surface ; we want to know whether they are moving away from 

 us or towards us ; and still further, we want to find out, if possible, 

 what changes, in their physical and chemical properties, the elements 

 with which we are acquainted have undergone under the influence 

 of the altered conditions which must exist in the celestial bodies. 

 Every sunsjwt, every solar prominence, is a study in which the un- 

 known quantities include not only the physical conditions of the solar 

 surface, but also the possibly changed properties, under these condi- 

 tions, of our terrestrial elements. The spectroscope is rapidly becom- 

 ing our thermometer and pressure gauge ; it has become a physical 

 instrument. 



The application of the spectroscope to the investigation of the 

 nature of celestial bodies has always had a great fascination to the 

 scientific man as well as to the amateur ; for in stars and nebula3 one 

 may hope to read the past and future of our own solar system. But 

 it is not of this application that I wish to speak to-day. 



As there is no other instrument which can touch the conditions of 

 the most distant bodies of our universe, bodies so large that their size 

 Vol. IX. (No. 73.) 2 m 



