10 ASTRONOMY. 



will become nearly circular. In this state, however, 

 it will not long continue; but in the course of ages 

 again return to the form of an ellipsis, of an eccen- 

 tricity that will vary as before, so as never to exceed 

 a certain limit.* 



Stars of a Variable Lustre. 



There are particular stars that shine with a vari- 

 able and periodical lustre, white, yellow, blue, and 

 red, with all their different shades. Baron Zach 

 has published a catalogue of 28 of these changeable 

 stars. 



The star Algol, the most remarkable of the vari- 

 able stars, when its light is smallest, appears of the 

 fourth magnitude, but when brightest, of the second. 

 The complete change appears to occupy a period of 

 only eight hours. 



Great Weight of the Solar Inhabitants. 



As the diameter of the sun (883,000 miles) is 111 

 times greater than that of the earth, a body at its 

 surface would fall through 450 feet in a second of 

 time ; so that if there be any human inhabitants re- 

 siding there, each individual of moderate size must 

 weigh at least two tons. 



The bulk of the sun is 1,300,000 greater than that 

 of the earth. 



The Moon. 



The moon when viewed through a good telescope, 

 has the appearance of an incinerated mass. 



* It is remarkable that the only facts perfectly certain are those 

 relating to the motions of the heavenly bodies, which are never- 

 theless so many millions of miles removed from our immediate 

 cognizance ; over every thing else there hangs a cloud of doubt 

 and mystery. 



All instances of celestial motion are instances of curvilinear 

 motion. 



