xxxv lii 



INTRODUCTION TO ASTRONOMY. 



Fig. 7. 



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vessel in which we sail. It is only when some obstacle impedes our 

 motion that we are conscious of moving ; and were you to close your eyes 

 while sailing on calm water, with a steady wind, you would not perceive 

 that you moved, for you could not feel it, and you could see it only by 

 observing the change of place of the objects on shore. So it is with the 

 motion of the earth: every thing on its surface, and the air that surrounds 

 it, accompanies it in its revolution it meets with no resistance, therefore 

 we are insensible of motion. 



The apparent motion of the sun and stars affords us the same proof of 

 the earth's motion that the crew of a vessel has of their motion from the 

 apparent motion of the objects on shore. Imagine the earth to be sailing 

 round its axis, and successively passing by every star, which, like the 

 objects on land, we suppose to be moving, instead of ourselves. In 

 balloons, the earth appears to sink beneath the balloon, instead of the 

 balloon rising above the earth. 



It is a law which we discover throughout Nature, and worthy of its 

 great Author, that all its purposes are accomplished by the most simple 

 means. We have no reason to suppose this law infringed, in order that 

 our earth may remain at rest, while the sun and stars move round us : 

 their regular motions, which are explained by the laws of attraction on 

 the first supposition, would be unintelligible on the last, and the order and 

 harmony of the universe be destroyed. What an immense circuit the sun 

 and stars would make daily, were their apparent motions real ! We know 

 many of them to be bodies more considerable than our earth ; for our eyes 

 vainly endeavour to persuade us, that they are little brilliants sparkling in 

 the heavens, while science teaches us that they are immense spheres, 



