98 



COSMOS. 



enumeration of these bodies, and of comets, longer than the 

 general nature of this work might warrant, I have not done 

 so undesignedly. The diversity existing in the individual 

 characteristics of comets has already been noticed. The im- 

 perfect knowledge we possess of their physical character, 

 renders it difficult in a work like the present, to give the 

 proper degree of circumstantiality to the phenomena, which, 

 although of frequent recurrence, have been observed with such 

 various degrees of accuracy, or to separate the necessary from 

 the accidental. It is only with respect to measurements and 

 computations that the astronomy of comets has made any 

 marked advancement, and consequently a scientific considera- 

 tion of these bodies must be limited to a specification of the 

 differences of physiognomy and conformation in the nucleus 

 and tail, the instances of great approximation to other cos- 

 mical bodies, and of the extremes in the length of their or- 

 bits and in their periods of revolution. A faithful delineation 

 ef these phenomena, as well as of those which we proceed to 

 consider, can only be given by sketching individual features 

 with the animated circumstantiality of reality. 



Shooting stars, fire balls, and meteoric stones are, with 

 great probability, regarded as small bodies moving with planet- 

 ary velocity, and revolving in obedience to the laws of general 

 gravity in conic sections round the Sun. When these masses 

 meet the Earth in their course, and are attracted by it, they 

 enter within the limits of our atmosphere in a luminous 

 condition, and frequently let fall more or less strongly heated 

 stony fragments, covered with a shining black crust. When 

 we enter into a careful investigation of the facts observed at 

 those epochs when showers of shooting stars fell periodically 

 in Cumana in 1799, and in North America during the years 

 1833 and 1834, we shall find that fire balls cannot be con- 

 sidered separately from shooting stars. Both these phenomena 

 are frequently not only simultaneous and blended together, but 

 they likewise are often found to merge into one another, the 

 one phenomenon gradually assuming the character of the other 

 alike with respect to the size of their discs, the emanation of 

 sparks, and the velocities of their motion. Although explod- 

 ing smoking luminous fire balls are sometimes seen even in the 

 brightness of tropical daylight,* equalling in size the apparent 



* A friend of mine, much accustomed to exact trigonometrical mea- 

 surements, was in the yea* 1788 at Popayan, a city which is 2 26' N. L. 



