Lesson via.] JUPITER. 37 



piter had four satellites, which he called Medicean 

 Stars, m honour of the family of the Medici, his 

 patrons. This was a discovery very important in 

 its consequences, as it afforded a method of deter- 

 mining the longitude of places on the earth (by 

 means of the eclipses of these satellites) with 

 greater facility and accuracy than by any other 

 method yet known. These eclipses also enabled 

 M. Roemer to discover and ascertain the progres- 

 sive motion of light; and hence Dr. Bradley was 

 enabled to explain an apparent motion in the fixed 

 stars, which could not otherwise have been ac- 

 counted for, and which philosophers characterize 

 by the term aberration. 



LESSON 



