722 



THE AURORA BOREALIS. 



The portion of the earth's surface selected for comparison in- 

 cludes the whole area from which there are long continued series 

 of observations, except from a few places in the north, and the 

 results of this comparison are shown in a plate giving the curve 

 for each of the three phenomena. 



There is a very close correspondence of the curves, and the 

 coincidence in the times of maximum and minimum is remarkable. 

 The auroral maximum generally occurs a little later than the 

 magnetic maximum, and it appears that the connexion between 

 the auroral and magnetic curves is moi'e intimate than between 

 the auroral and sun-spot curves. 



Date of Maximum. 



Date of Minimum. 



Sun 

 Spots. 



Magnetic 

 DecHnation. 



Auroras. 



Sun • 

 Spots. 



Magnetic 

 Declination. 



Auroras. 



1778 



1788-5 



1804 



1816-5 



1829-5 



1837 



1848-5 



1860 



1870 



1777 



1787 



1803 



1817-5 



1829 



1838 



1848-5 



1859-5 



1870-5 



1778 



1787-5 



1804-5 



1818 



1830 



1840 



1850*5 



1859-5 



1870-5 



1784 



1798 



1810 



1823 



1833-5 



1843-5 



1856 



1867 



1784 



1799-5 

 Wanting. 



1823-5 

 Wanting. 



1844 



1856 



1867 



1784 

 1798 

 1811 

 * 1823 

 1834-5 

 1843-5 

 1856 

 1867 



From the close connexion between the times of maxima and 

 minima Professor Loomis concludes — " That the black spot is a 

 " result of a disturbance of the sun's surface, which is accom- 

 " panied by an emanation of some influence from the sun, which 

 ^' is almost instantly felt upon the earth in an unusual disturbance 

 " of the earth's magnetism and a flow of electricity, developing the 

 " auroral light in the upper regions of the earth's atmosphere." 



12. The Geographical Distribution of Aurora. 



M. Petermann's Mitlheilungen, vol. 20, 1874, IX., contains a 

 paper on this subject by Prof. Fritz, with map, from which it 

 appears that the northern limit of Auroras chosen by Prof. Loomis 

 nearly coincides, except in England, with the line of frequency 

 represented by 10 in Prof. Fritz's paper. This line in Prof. Fritz's 

 paper nearly passes through Toronto, Manchester, and St. Peters- 

 burgh. Prof. Loomis places it as far north as Edinburgh. On a 

 line across Behring's Straits and coming down below 60° N. in 

 America and the Atlantic, and passing just north of the Hebrides 

 to Drontheim, and including the most northern points of Siberia, 

 the frequency is represented by 1 00. 



Within this another zone is drawn, indicating the zone of 

 greatest frequency and intensity. 



This zone passes just south of Point Barrow, in latitude 72° N., 

 and by the Great Bear Lake to Hudson's Bay, where it reaches a 



