14 ASTRONOMY. 



which our own solar system is placed ; the luminous 

 tracts that constitute the galaxy being a projection of 

 the nebulae on the concave surface of the sky, as 

 seen from the solar system which it incloses. 



Comparative Distance of the Fixed Stars. 



The same great astronomer concluded, that a star 

 of the first magnitude would just become visible to 

 the naked eye if removed to 12 times its present dis- 

 tance, and by the most powerful telescope if removed 

 to 2300 times that distance. 



Motion of what are called the Fixed Stars. 



A change of place (a deviation to the south) in the 

 declination of some of the principal fixed stars, Mr. 

 Pond thinks is taking place. 



Binary Systems. 



Mr. Herschel and Mr. South have clearly esta- 

 blished the existence of binary systems, in which two 

 stars perform to each other, the offices of sun and 

 planet. ,They have ascertained the periods of rota- 

 tion of more than one pair, and have also observed 

 the occultations of stars behind each other, and the 

 motions of revolving systems, detecting among them 

 real motions sufficiently rapid to become measurable 

 quantities in very short intervals of time. 



Figure of the Earth. 



The equatorial diameter of the earth is to the 

 polar diameter as 179 to 178, and the equatorial ra- 

 dius of the earth about eight leagues longer than the 

 polar. 



Length of the Pendulum. 

 The following are some of the difficulties that 



