104 On the Formation of the Tails of Comets. 



145. Atheropogon apludoides, Muhl. 



146. Atheropogon papillosum (n. sp.): culmis ceespitosis basi 

 foliatis ; foliis lanceolato-linearibus planis margine et ad nervum 

 medianum infra supraque ex papillis serrato-ciliatis ; spicis 1-3 

 subterminalibns biserialibus unilateralibus multifloris ; glumis 

 papilloso-hispidis ; valva corolla3 perfects exteriore trifida, valva 

 corollas neutrius brevissima hyalina ex basi triaristata. 



Sandy soil, Beardstown, 111. — Very near A. oligostachyus, 

 Nutt., and resembling it closely, but distinct by the broader and 

 hispid (not setaceous and smooth) leaves, the hispid (not pubes- 

 cent) glumes, and the hyaline glume of the abortive floret (not 

 half as large as in A. oligostachyus.) 



147. Andropogon scoparius, Michx. 



148. Poa hirsuta, Michx. 



149. Poa pectinacea, Michx. ? 



149, b. Hordeum pusillum, Nutt. 



150. Woodsia Perriniana, Hook. 



Art. XIV. — On the Mode of Formation of the Tails of Comets ; 

 by William A. Norton, Professor of Mathematics and Natural 

 Philosophy in Delaware College. 



It is not my design, in the present article, to furnish a complete 

 theory of the process by which the tails of comets are formed 

 from their heads. This cannot be attempted, it is presumed, 

 with any reasonable hope of success, until more facts relative to 

 the structure and phenomena of comets have been accumulated. 

 But little more will now be undertaken, than to disprove the 

 commonly received notion that the tail and head of a comet form 

 one connected mass, revolving as one body, and to establish the 

 opposing doctrine, that the tail is made up of particles of matter 

 continually in the act of flowing away from the head. To do 

 this intelligibly and effectually, however, it will first be necessary 

 to treat briefly of the 



Physical Constitution of Comets. 



What I have to offer upon this preliminary topic, may be con- 

 veniently arranged under the following heads ; viz. 1. The na- 



