220 



AURORA BOREALIS. 

 Table III. 



If we combine the last seven observations of the preceding table, we shall 

 find that tke lower liinit of the auroral light was elevated fifty miles above the 

 earth's surface, and that its southern margin was vertical over the parallel of 

 25° 15' north latitude in Florida. Now the dip of the magnetic needle in 

 Florida, in latitude 25° 15', is 55'^ 40' ; and if we draw G H, making an angle 

 of 55° 40' with the curve line E Y, which represents a portion of the earth's sur- 

 face, and assume that the line Gr II represents the southern boundary of the 

 auroral illumination, and that the first five observations of Table III were made 

 upon the point H, we shall find that the upper limit of the auroral light was 

 elevated 495 miles above the earth's surface, and that its southern margin was 



^0 :§ 



vertical over the parallel of 22° 30' north latitude in Cuba.* Combining these 

 results with the numerous observations of this aurora contained in the American 

 Journal of Science, A'olume 32, we find that the aurora of September 2, 1859, 

 formed a belt of light encircling the northern hemisphere, extending southward 

 in North America to latitude 22^'^, and reaching to an unknovvu distance on the 

 north ; and it pervaded the entire interval between the elevations of 50 and 500 

 miles above the earth's surface. This illumination consisted chiefly of luminous 



* American Jom-nal ot Science, n. s., v. 32, pp. 319-322. 



