THE STELLAR UNIVERSE. 



than those of the first magnitude, because they are really smaller 

 orbs placed at the same distance ? or because, being intrinsically 

 equal in splendour and magnitude, the distance of those of the 

 seventh magnitude is so much greater than the distance of those 

 of the first magnitude that they are diminished in their apparent 

 brightness ? We know that by the laws of optics the light 

 received from a luminous object diminishes in a very rapid pro- 

 portion as the distance increases. Thus, at double the distance it 

 will be four times less, at triple the distance it will be nine times 

 less, at a hundred times the distance it will be ten thousand 

 times less, and so on. 



It is evident, then, that the great variety of lustre which 

 prevails among the stars may be indifferently explained, either by 

 supposing them objects of different intrinsic brightness and mag- 

 nitude, placed at the same distance ; or objects generally of the 

 same order of magnitude, placed at a greA,t diversity of distances. 



Of these two suppositions, the latter is infinitely the more 

 probable and natural ; it has, therefore, been usually adopted : 

 and we accordingly consider the stars to derive their variety of 

 lustre almost entirely from their places in the universe being at 

 various distances from us. 



26. Taking the stars generally to be of intrinsically equal 

 brightness, various theories have been proposed as to the positions 

 which would explain their appearance ; and the most natural and 

 probable is, that their distances from each other are generally 

 equal, or nearly so, and correspond with the distance of our sun 

 from the nearest of them. In this way the fact that a small 

 number of stars only appear of the first magnitude, and that the 

 number increases very rapidly as the magnitude diminishes, is 

 easily rendered intelligible. 



If we imagine a person standing in the midst of a wood, sur- 

 rounded by trees on every side and at every distance, those 

 which immediately surround him will be few in number, and 

 by proximity will appear large. The trunks of those which 

 occupy a circuit beyond the former, will be more numerous, 

 the circuit being wider, and will appear smaller, because their 

 distance is greater. Beyond these again, occupying a still wider 

 circuit, will appear a proportionally augmented number, whose 

 apparent magnitude will again be diminished by increased dis- 

 tance ; and thus the trees which occupy wider and wider circuits 

 at greater and greater distances will be more and more numerous, 

 and will appear continually smaller. It is the same with the 

 stars ; we are placed in the midst of an immense cluster of suns, 

 surrounding us on every side at inconceivable distances. Those 

 few which are placed immediately about our system, appear 

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