112 COSMOS. 



difficulty 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 de- 

 grees of accuracy, or to separate the necessary from the acci- 

 dental. It is only with respect to measurements and compu- 

 tations that the astronomy of comets has made any marked 

 advancement, and, consequently, a scientific consideration of 

 these bodies must be limited to a specification of the differencep. 

 of physiognomy and conformation in the nucleus and tail, the 

 instances of great approximation to other cosmical bodies, and 

 of the extremes in the length of their orbits and in their periods 

 of revolution. A faithful delineation of these phenomena, as 

 well as of those which we proceed to consider, can only be 

 given by sketching individual features with the animated cir- 

 cumstantiality of reality. 



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

 probability, regarded as small bodies moving with planetary 

 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 con- 

 dition, 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 Cu- 

 mana in 1799, and in North America during the years 1833 

 and 1834, we shall find that Jire-balls can not be considered 

 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 disks, 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,*" equaling in size the ap- 



* A IVieudof mine, much accustomed to exact trigonometrical meas- 

 urements, was in the year 1788 at Popayan, a city which is 2^^ 26' 

 north latitude, lying at an elevation of 5583 feet above the level of the 

 sea, and at noon, when the sun was shining brightly in a cloudless sky, 

 saw his room lighted up by a fire-ball. He had his back to the window 

 at the time, and on turning round, perceived that great part of the path 

 traversed by the fire-ball was still illuminated by the brightest radiance. 

 Different nations have had the most various terms to express these phe" 

 nomeua: the Germans use the word Sternschnnppe, literally star snvff 

 —an expressbn well suited to the physical views of the vulgar in forma 



