THE NEBULAR HYPOTHESIS. 657 



Until recently the light from the heavenly bodies, even when col- 

 lected by the largest telescopes, conveyed to us but very meagre in- 

 formation. With regard to the moon, sun, and some of the planets, in 

 addition to their form and size, we have been able, by this means, 

 to obtain some slight knowledge of their physical structure. But, 

 with reference to the myriads of stars, clusters, and nebula?, which 

 people the depths of space, the telescope reveals little more than 

 variety in color, brightness, and shape. (In relation to the nebulae, 

 this was' illustrated by diagrams contrasting the appearance presented 

 by the same objects when viewed in the telescopes of Sir John Her- 

 schel and of Lord Rosse.) 



The discovery of " Spectrum Analysis " the optical Analysis of 

 Light enables us to interpret symbols and indications hidden within 

 the light itself. Wherever the tiny waves of light the swift messen- 

 gers of the celestial realms can penetrate, they bear with them intel- 

 ligence of their orisrin ! " Bodies, so remote that astronomers fail to 

 give us an idea of their distance, are brought, as it were, into our 

 grasp, and are analyzed with certainty ! We recognize in them the 

 same elements which compose the soil we tread the water we drink 

 the air we breathe ! " 



Before proceeding to explain the manner in which this new method 

 of investigation decides the question of the existence of true nebulous- 

 masses in the regions of space, it is necessary to recall certain well- 

 known and long-established principles in optical science. In 1675, the 

 immortal Newton demonstrated the composite nature of solar light. 

 When a ray of sunlight is made to pass through a glass prism, it is re- 

 fracted and spread out into a fan-like band, so as to exhibit exquisite 

 gradations of color, from red at one end to violet at the other. Thia 

 constitutes the Prismatic or Solar Spectrum. In 1802, Wollaston dis- 

 covered that this spectrum is not continuous, but is interrupted by a 

 number of dark lines. In 1815, Fraunhofer, by great improvements in 

 the optical arrangements employed, rediscovered these lines ascer* 

 tained that their relative distances from each other were fixed for sun- 

 light and succeeded in mapping no less than fifty of them as belong* 

 ing to the solar spectrum. Since that time, the number of these lines 

 has been increased to thousands. The sagacious Fraunhofer traced 

 these same dark fixed lines in reflected as well as in direct solar light : 

 he found them quite unaltered in position, in the spectrum of moon- 

 light and Venus-light. He, likewise, discovered, that the spectra of 

 the fixed stars contained dark lines differing from those seen in the 

 solar spectrum. He thence drew the important conclusion that these 

 lines have their origin in the luminary. Fraunhofer thus opened the 

 inquiry; but the explanation and import of these lines were reserved 

 for a subsequent epoch. 



Modern investigations have established the existence of three or- 

 ders of spectra depending upon the source of the light : 1. A continu- 

 vol. 11. 42 



