THE SIDEREAL UNIVERSE. 701 



of light starting from one of them would take 2000 years to 

 reach us. 



Yet human investigation penetrates much farther than 

 this. When the observer carries his investigations more 

 deeply into immensity, when he reaches those nebulae which 

 lie on the confines of space, the distances are so great that 

 they confound the imagination, and figures no longer suffice 

 to represent them. According to calculations, says Hum- 

 boldt, which are not devoid of probability, light, notwith- 

 standing its tremendous speed, requires more than two mill- 

 ions of years to traverse the enormous distance which sepa- 

 rates us from these stars. Hence, while the telescope still 

 displays to our eyes the luminous gleam of one of these 

 nebula?, it may be that more than two million years ago this 

 mysterious body was extinguished in space. Thus the his- 

 tory of the heavens traversing the night of time passes 

 through ages, and then appears to us like contemporaneous 

 events ! This is, as has been said, the most authentic proof 

 of the immense antiquity of matter. 



CHAPTER II. 



THE NEBULAE. 1 



The investigation of the universe is not limited to the 

 stars. By means of large telescopes we discover at the far- 



1 " Nebulae " is a name applied to certain celestial objects from their cloud-like 

 appearance, which gives them a resemblance to faint comets or specks of luminous 

 fog. Many nebula?, though cloud-like to the naked eye, and even to many tele- 



