ASTRONOMY AS A SCIENCE. THE SUN. 117 



before, the beam of light from Sirius (reaching the 

 earth after a passage of years through intervening 

 space) has been made to yield a photographic image 

 of the star and a spectrum with lines corresponding in 

 part with those of the sun proving thereby the exist- 

 ence and identity of the chemical rays, and the presence 

 of certain material elements in this remote part of crea- 

 tion, which recent discoveries have shown to be in 

 common to the earth and the sun. 



The researches now directed to this great centre of 

 our own system similarly attest the genius and suc- 

 cessful labours of modern astronomy. Some thirty 

 years ago it seemed as though our knowledge of the 

 sun had reached its highest possible attainment. Its 

 distance from the earth, its magnitude and specific 

 gravity, the laws by which it governs the orbital 

 motions of the planets and comets, its own proper 

 motion in space, the time of rotation on its axis, 

 and the dark spots on its surface indicating this 

 time ; its influence on the ocean-tides, &c. all these 

 things had been either exactly or approximately de- 

 termined. The light and heat of which it is the per- 

 petual fountain, though comprehended in their origin 

 only as emanations of force, had been the subjects of 

 admirable analysis in their passage through space in 

 the solar spectrum, and in their influences on matter, 

 living or lifeless, on our own globe. Speculation on 

 some points went further, but more exact science 

 for a time halted here. 



It was but a halt, however, and this at the threshold 

 of what may almost be called a new science of the sun, 



