THE FIXED STARS. 117 



a velocity of eight hundred eighty thousand miles an hour ; 

 but according to calculations made since the days of New- 

 ton, its motion has been computed to be one million two 

 hundred forty miles an hoar. 



The comet of 1758 was looked for with great interest by 

 astronomers, because its return had been predicted. But it 

 is worthy of remark, that what, in this century, excited only 

 the curiosity of astronomers and mathematicians, had been 

 regarded four revolutions before, in 1456, with feelings of 

 horror. Its long train spread consternation over all Europ6, 

 already terrified at the success of the Turkish arms, which 

 had just destroyed the great empire. Pope Callixtus, on this 

 occasion, ordered a prayer, in which the comet and the 

 Turks were included in the same anathema. 



Questions. — 1. What are comets ? 2. How do they move ? 3. 

 What is said of the train of a comet? 4. How do comets appear 

 through a telescope ? 5. Wliat is said of the number of comets ? 6. 

 What is known of the orbits of cornets ? 7. What is said of the comet 

 of 1680 ? 8. What is worthy of remark with respect to the comet of 

 1758.' [Note. The comet of 1758 is expected to return in 1834.] 



LESSON 54. 



The Fixed Stars. 



Neb'ula, (plural, nebula?,) a cloud of obscure light in the heavens ; 

 some nebulae consist of clusters of telescopic stars, others ap- 

 pear as luminous spots of different forms. Sir'ius, the dog-star. 



Those luminous bodies which always appear in the hea- 

 vens at the same distance from each other, are called fixed 

 stars ; because, with the exception of a few, which, in a 

 course of years, appear to change their places, it has not 

 been discovered, that they have any proper motion of their 

 own. When viewed through a telescope they appear as 

 points of small magnitude ; they must be at such an immense 

 distance, therefore, as to be invisible to the naked eye, if 

 they borrowed their light ; as is the case with the satellites 

 of Jupiter and Saturn, although they appear of very distin- 

 guishable magnitu4e through a telescope. The stars are 

 probably suns, around each of which revolve primary and 

 secondary planets, as about our sun. They are distinguish- 

 able from the planets by their twinkling. 



