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 Rendus 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 
the earth. On the other hand, we have estimates which give it 
an elevation no greater than that of the ordinary upper clouds, oF 
anions it iain the limit of a few miles. Such is that of 
rquharson of Scotland, who supposes the ordinary contin 
patty be 2000 feet at the base, and 4000 or 5000 at the 
