Remarks on the Tails of Comets. 59 



a circumference of eighteen inches ; they are only half an inch apart at 

 the socket, and project right and left, with the concavity forward. The 

 teeth have the mamrailiose or mastodon shape and conformation, and are 

 three and a half inches in length by two and a half in breadth. The lower 

 jaw is wanting. 



There is an os humeri, probably of a megalonyx, which measures in 

 length one foot eight inches, the ulna of the same animal, and also other 

 bones, probably the radii, with some of the last phalanges. 



Dr. Horner stated, that his sketch of this rich accumulation of fossil 

 remains and their examination were very imperfect, and the less instruc- 

 tive to him, for the want of standards of comparison in perfect skeletons, 

 and in plates, neither of which means of elucidation exist in St. Louis, 

 and he expressed a hope, that " their diligent and deserving collector 

 would furnish the scientific world with exact plates of such as are rare or 

 unknown." 



Art. Y .—Additiojial Remarks on the Tails of Comets ; by Wm. 

 Mitchell, of Nantucket, Mass. 



It is a weakness common, I believe, to most men, to adhere 

 with more or less pertinacity to first impressions ; it is manifested 

 in childhood, and is often strengthened by age. From this delu- 

 sive error, in the discussion in which I now engage, I can scarce- 

 ly hope, though I strongly desire to be entirely free. The end 

 of all inquiry should be truth, which is the only legitimate object. 



In Vol. XXXVIII, No. 1, I was indulged with the occupancy of 

 a few pages for the publication of an essay on the tails of comets. 

 The object of the article and its only hope, was to invite the at- 

 tention of those familiar with this and kindred subjects, to a very 

 simple, and to myself, satifactory explanation of the phenome- 

 non ; being principally the result of my own observations on the 

 comets visible in this part of the world during the last thirty 

 years; viz. that their tails are form.ed by the sun^s rays, slightly 

 refracted by the nucleus in traversing the envelope of the comet, 

 and ujiiiing in an infinite number of points beyond it, throwing 

 a stronger than ordinary light o?i the ethereal medium, near to, 

 or more remote from the comet, as the ray from, its relative position 

 and direction is more or less refracted. In support of this theory, 

 I adduced very briefly the facts and the reasoning which had es- 

 tablished it in my own mind. 



