252 PROGRESS OF SCIENCE. 



ascertain that the sun's spots are immense hollows or de- 

 pressions a fact which would tend to corroborate the cyclone 

 theory. It has made solar and stellar physics a possibility 

 and a reality. Not simply has it revealed, as we just saw, 

 the chemical components and some of the physical arrange- 

 ments of celestial bodies ; but it has also revealed the 

 existence of solar systems unsuspected hitherto such as 

 binary systems, one body of which is a dark star the 

 existence of dark suns, already suspected, being thereby 

 demonstrated ; and with their existence, the cause of the 

 increase and decrease of light in some of the variable stars 

 was explained, the decrease of light being due to the 

 eclipse of the luminous by the dark star. It has further 

 revealed the rate of velocity of motion of stars and nebulae, 

 and particularly that of double stars (within less than half 

 a mile per second of time),* together with the distance 

 from each other of such stars, the magnitude of their 

 bodies, the magnitude and the ellipticity of their orbits, 

 hence the time of their revolution. The spectroscope 

 has even revealed the approximate temperature and almost 

 the evolutionary stage of many celestial bodies. THREE 

 THINGS this truly marvellous instrument seems to have 

 MADE PLAIN : (l.) the common or identical nature of the 

 substances composing the cosmos ; (u.) the variety of its 

 plan and construction; (ill.) the identity of the forces and 

 principles governing it. Many of the facts brought to our 

 knowledge by the spectroscope seemed, only thirty years 

 ago, for ever to lie beyond the scope of human achieve- 

 ment and even beyond the conception of human intellect. 

 To the genius of Kirchhoff mainly we are indebted for these 

 scientific wonders. 



1824 1 8 . Huggins (Dr.) has advanced celestial physics 



by his fine SPECTROSCOPIC STUDY of the HEAVENLY BODIES 

 many of the results described in our notice of Kirchhoff 

 being due to him. He found the spectra of numerous 

 irresolvable nebulae to consist of three or four bright lines 



* Some proceed at the rate of 23, 25, 26 miles per second ; one 67 

 miles ; our own solar system travels through space at the rate of 18 miles 

 per second, besides the motion particular to each body separately. 



