288 Aurora Borealis of November 14, 1837. 



mit, to about one hundred and sixty geographical miles. It must 

 be observed, however, that we know not how far south of Rich- 

 mond the Aurora was vertical. If it extended a single degree 

 farther south, we should infer an altitude of but very little more 

 than one hundred miles. 



The result of a calculation similar to the foregoing, made in 

 Europe upon the Aurora of Oct. 18, 1836, by M. Wartmann of 

 Geneva, is stated in the Comptes Retidus of April 17, 1837, to 

 give an altitude of two hundred leagues, or about six hundred 

 miles. 



Two observers may obtain a parallax of the summit of the 

 highest column observed due north, or of the extreme altitude in 

 that direction of the general mass of illuminated vapor, when the 

 Aurora is vertical to neither. This will give the distance of the 

 Aurora from either observer, and by consequence its perpendicu- 

 lar height at the point where it is vertical. The mode of calcu- 

 lation, it must, after all, be confessed, is far from being so accurate 

 as could be desired. 



Mr. Dalton, in his Meteorological Essays, estimates the altitude 

 of the summits of the auroral columns, at about one hundred and 

 fifty English miles. Mr. Dalton's observations were made upon 

 an auroral arch, at right angles to the magnetic equator, and he 

 assumes this arch, and all others similar, without proof, to have an 

 altitude equal to that of the highest extremities of the ordinary 

 columns. Mr. Dalton supposes the auroral columns to be cylin- 

 drical, to stand nearly parallel to each other, in the line of the dip, 

 and to have a length about ten times as great as their diameter, 

 and about equal to the height of their bases above the surface of 

 the earth. Allowing the auroral columns to be all of equal di- 

 mensions, a concession, however, which we cannot possibly make, 

 Mr. Dalton's conclusions are pretty well sustained by observation, 

 and by mathematical demonstration. 



Mairan supposes the mean altitude of the Aurora to be one hun- 

 dred and seventy-five leagues, or about five hundred miles ; while 

 Euler places it more than one thousand miles above the surface of 

 the earth. On the other hand, we have estimates which give it 

 an elevation no greater than that of the ordinary upper clouds, or 

 confine it within the limit of a few miles. Such is that of Mr. 

 Farquharson, of Scotland, who supposes the ordinary elevation of 

 the Aurora to be 2000 feet at the base, and 4000 or 5000 at the 



