THE VISIBLE STARS. 5QJ 



Are we to suppose, then, that this relative brightness which we perv 

 really arises from any difference of intrinsic splendor between the object* tin-ni- 

 sei ves, or does it, as it may equally do, arise from their difference of dislan 

 Are the stars of the seventh magnitude so much less bright and conspicuous 

 than those of the first magnitude because they are really smaller orbs placed 

 at the same distance, or because, being intrinsically equal in splendor, th< 

 tance of those of the seventh magnitude is so much greater than the disi 

 of those of the first magnitude that they are diminished in their apparent 

 brightness ? We know that by the laws of optics the brightness of a luminous 

 object diminishes in a very rapid proportion as the distance increases. Thus 

 at double the distance the brightness will be four times less, at triple the dis- 

 tance 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 brightness which prevails among the 

 stars may be indifferently explained, either by supposing them objects of differ- 

 ent intrinsic brightness and magnitude, placed at the same distance, or objects 

 generally of the same order of magnitude placed at a great diversity, of distances. 



Of these two suppositions, the latter is infinitely the most probable and nat- 

 ural ; it has, therefore, been usually adopted : and we accordingly consider the 

 stars to derive their variety of brightness almost entirely from the positions 

 assigned to them in the universe being at various distances from us. 



Taking the stars generally to be intrinsically the same in brightness, varipus 

 theories have been proposed as to the positions which would explain their ap- 

 pearances ; 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, surrounded 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 or 

 stumps of those which occupy a circuit beyond the former will be more nu- 

 merous, the circuit being wider, and will appear smaller, because their dis- 

 tance is greater. Beyond these again, occupying a still wider circuit, will ap- 

 pear a proportionally augmented number, whose apparent magnitude will again 

 be diminished by increased distance ; and thus the trees which occupy wider 

 and wider circuits at greater and greater distances will be more and more nu- 

 merous, 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 immedi- 

 ately about our system appear bright and large, and we call them stars of the 

 first magnitude. Those which lie in the circuit beyond, and occupying a 

 wider range, are more numerous and less bright ; and we call them stars of the 

 second magnitude. And there is thus a progression increasing in number and 

 distance and diminishing in brightness, until we attain a distance so great that 

 the stars are barely visible to the naked eye. This is the limit of vision, 

 is the range of the universe which the eye in its natural condition is destined 

 to behold ; but an eye has been given us more potent still, and of infinitely 

 wider range, the eye of the mind. The telescope, a creature of the under- 

 standing, has conferred upon the bodily eye an infinitely augmented range, and, 

 as we shall presently see, has enabled us to penetrate into realms of thi 

 universe, which, without its aid, would never have been known to us. 

 let us pause for the present and dwell for a moment upon that range of space 

 which comes within 'the scope of natural vision. 



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