PORTION OF THE COSMOS. VISUAL POWER. 43 



II. 



NATURAL AND TELESCOPIC VISION SCINTILLATION OF STARS 



VELOCITY OF LIGHT RESULTS OF PHOTOMETRY. 



IT is only within the last two centuries and a half that the 

 artificial telescopic enhancement of the visual power of the 

 eye, the organ by which we contemplate the Universe, 

 has afforded the grandest of all aids and instruments for the 

 recognition of the contents of space, and for the discovery 

 of the form, physical constitution, and mass of the planets 

 and of their satellites. The first telescope was constructed 

 in 1608, seven years after the death of the great observer 

 Tycho Brahe. Jupiter's satellites, the solar spots, the 

 phases of Yenus, Saturn's ring, telescopic clusters of stars, 

 and the nebula in Andromeda, ( 90 ) had already been suc- 

 cessively discovered by means of the telescope, when, in 

 1634, the French astronomer Morin (worthy of honourable 

 mention in reference to observations of longitude), thought 

 of attaching a telescope to the alidade of a measuring in- 

 strument, and looking for Arcturus in the day-time. ( 91 ) 

 The improvement of the graduation of the limbs of instru- 

 ments would have failed, either wholly or in great part, in 

 attaining its principal object, viz. greater precision in obser- 



