198 COSMOS. 



Southern lights have often been seen in England by the in 

 telligent and indefatigable observer Dalton, and northern lights 

 have been observed in the southern hemisphere as far as 45^ 

 latitude (as on the 14th of January, 1831). On occasions 

 that are by no means of rare occurrence, the equilibrium at 

 both poles has been simultaneously disturbed. I have discov- 

 ered with certainty that northern polar lights have been seen 

 within the tropics in Mexico and Peru. "VVe must distinguish 

 between the sphere of simultaneous visibility of the phenom- 

 enon and the zones of the Earth where it is seen almost night- 

 ly. Every observer no doubt sees a separate Aurora of his 

 own, as he sees a separate rainbow. A great portion of the 

 Eartk simultaneously engenders these phenomena of emana- 

 tions of light. Many nights may be instanced in which the 

 phenomenon has been simultaneously observed in England 

 and in Pennsylvania, in Rome and in Pekin. When it is 

 stated that Auroras diminish with the decrease of latitude, 

 the latitude must be understood to be magnetic, and as meas- 

 ured by its distance from the magnetic pole. In Iceland, in 

 Greenland, Newfoundland, on the shores of the Slave Lake, 

 and at Fort Enterprise in Northern Canada, these lights ap- 

 pear almost every night at certain seasons of the year, cele- 

 brating with their flashing beams, according to the mode of 

 expression common to the inhabitants of the Shetland Isles, 

 " a merry dance in heaven."* While the Aurora is a phe- 

 nomenon of rare occurrence in Italy, it is frequently seen in 

 the latitude of Philadelphia (39° 57'), owing to the southern 

 position of the American magnetic pole. In the districts 

 which are remarkable, in the New Continent and the Sibe- 

 rian coasts, for the frequent occurrence of this phenomenon, 

 there are special regions or zones of longitude in which the 

 polar light is particularly bright and brilliant, f The exist- 



of Buchtarminsk, so similarly developed, that we must regard the in 

 (luences producing it as very w^idely distributed, and as depending on 

 general natural forces. See the important observations of Kamtz ( Var- 

 lesungen uber Metcorologie, 1840, s. 146), and the more recent ones of 

 Martins and Bravais {MHiorologie, 1843, p. 117). In south polar bands, 

 composed of very delicate clouds, observed by Arago at Paris on the 

 23d of June, 1844, dark rays shot upward from an arch running east 

 and west. We have already made mention of black rays, resembling 

 dark smoke, as occurring in brilliant nocturnal northern lights. 



* The northern lights are called by the Shetland Islanders ''the 

 merry dancers." (Kendal, in the (Quarterly Journal of Science, new 

 series, vol. iv., p. 395.) 



t See Muncke's excellent work in the new edition of Gehler's Physik 

 iVorterbiich, bd. vii., i., s. 1 13-268, and especially s. 158. 



