354 A SHORT HISTORY OF SCIENCE 



spectra, and in 1879 published his paper On the Photographic Spectra 

 of Stars. The results were arranged and discussed with reference 

 to their bearing on stellar evolution. Hale. 



The first application of the spectroscope to the corona of the 

 sun was made in 1868 by Janssen and Lockyer, independently, re- 

 vealing the chemical composition of the solar prominences as 

 chiefly hydrogen, calcium, and helium. 



ELECTRICITY AND MAGNETISM: FARADAY, GREEN, AMPERE, 

 MAXWELL. Seebeck (1770-1831) in his work On the Magnetism 

 of the Galvanic Circuit published a first account of the magnetic 

 field illustrated by magnetized iron filings and later so fruitfully 

 investigated by Faraday. The sciences of electricity and mag- 

 netism had originated in the latter part of the eighteenth century 

 with Coulomb's use of the torsion-balance, by means of which he 

 made accurate comparison between the attractive or repulsive 

 forces exercised by electrified and magnetized bodies, and the 

 mechanical forces required to twist wires. Thus he found the first 

 definite units, a process carried much farther by Gauss and Weber. 



Ampere (1775-1836) stimulated by Oersted's discovery of the 

 effect of the electric current on magnets, published in 1820 a 

 fundamental discussion of electrodynamics and soon after enun- 

 ciated his celebrated law : 



Two parallel and like directed currents attract each other, while 

 two parallel currents of opposite directions repel each other. 



He also succeeded in expressing the quantitative relations in- 

 volved by a mathematical formula. 



Faraday, one of the most distinguished investigators in the 

 whole history of physical science, rescued electricity from the 

 mysterious notion of currents acting on each other through empty 

 space, by the fruitful conception of a magnetic field, of which a 

 new and comprehensive mathematical theory was gradually worked 

 out by Maxwell. Faraday's discoveries were so far-reaching that 

 they have even been coupled with the law of the conservation of 

 energy and Darwin's theory of descent as the greatest scientific 

 ideas of the latter half of the century. He observes : 



