prevalent Disorders, tyc, with Volcanic Emanations, 433 



nous cloud, like a square table, nearly in the zenith, from 

 which were emitted large streams of light. 



Professor Olmsted considers these auroral lights as proceed- 

 ing from the tail of his comet. Why, then, were they not seen 

 all over the United States ? But the fact is, that these auroral 

 lights were very low in the atmosphere in some places. At 

 Philadelphia one was 15° high, and very faint; at Germans- 

 town, not six miles off, it was 45°, and very bright. The 

 upper part of this aurora was not, therefore, more than 2 T ^ 

 miles from the surface of the earth. The curved appearance 

 of some of the meteoric trains is also an objection to the 

 theory of the comet : in that case all must have been straight. 



Mr. Espy refutes Professor Olmsted's calculation about the 

 condensation of the air by bodies falling, as he has supposed. 

 That calculation is founded on Leslie's formula ; but Olmsted, 

 mistaking " volume " for " weight" has made the heat pro- 

 duced by the sudden condensation of the air to be 46080° 

 centigrade, instead of 50°, nearly 1000 times too much ! This, 

 if true, would have involved another important result; namely, 

 that, by rarefying and condensing air, a temperature might be 

 produced many thousand times both higher and lower than 

 has ever been obtained, (p. 14.) 



Mr. Espy objects to Professor Olmsted, that his theory does 

 not account for the change of temperature accompanying the 

 phenomena. It is true he maintains that " the air descended 

 in large quantities from the region of perpetual frost ;" but he 

 forgets the result from Leslie's formula, that air thus con- 

 densed would have a temperature of 46080° centigrade ; up- 

 wards of 78000° Fahr. If Dalton's theory be correct, no 

 change in temperature would be thus produced; if Ivory be 

 right in his, a small increase would only take place. A sud- 

 den production of cold, therefore, is not an effect which would 

 follow of course from the descent of large quantities of air 

 from the regions of perpetual frost. Again, the fact undoubt- 

 edly contradicts this reasoning, because the temperature sank 

 previously to the meteoric shower. 



Professor Olmsted's explanation of the west wind is also re- 

 futed by Mr. Espy. It appears, Mr. Espy says, that the west wind 

 preceded the shower, and not, as Professor Olmsted says, suc- 

 ceeded it.* If large masses of a comet were to fall, they, being 

 independent of the earth's motion, would incline to the west in 

 their descent, and produce an easterly wind. Therefore, as 

 the meteors fell over a large tract sloping actually to the N. w., 



* Here both may be right, for westerly gales did succeed the display.— 

 W. B. C. 

 Vol. VIII. — No. 52. hh 



