THE CENTURY'S PROGRESS IN ASTRONOMY 



yet feels well assured that the solar system offers no 

 contradiction to those laws of growth and decay which 

 seem everywhere to represent the immutable order of 

 nature. 



ii 



Until the mathematician ferreted out the secret, it 

 surely never could have been suspected by any one that 

 the earth's serene attendant, 



"That orbed maiden, with white fire laden, 

 Whom mortals call the moon," 



could be plotting injury to her parent orb. But there 

 is another inhabitant of the skies whose purposes have 

 not been similarly free from popular suspicion. Needless 

 to say I refer to the black sheep of the sidereal family, 

 'that " celestial vagabond " the comet. 



Time out of mind these wanderers have been sup- 

 posed to presage war, famine, pestilence, perhaps the 

 destruction of the world. And little wonder. Here is 

 a body which comes flashing out of boundless space into 

 our system, shooting out a pyrotechnic tail some hun- 

 dreds of millions of miles in length ; whirling perhaps 

 through the very atmosphere of the sun at a speed of 

 three or four hundred miles a second ; then darting off 

 on a hyperbolic orbit that forbids it ever to return, or 

 an elliptical one that cannot be closed for hundreds or 

 thousands of years ; the tail meantime pointing always 

 away from the sun, and fading to nothingness as the 

 weird voyager recedes into the spacial void whence it 

 came. Not many times need the advent of such an ap- 

 parition coincide with the outbreak of a pestilence, or 

 the death of a Caesar, to stamp the race of comets as an 



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