4 6 MADEIRA METEOROLOGIC. PART iv. 



and watch all the night through, and night after night, 

 set themselves steadily to note the number of auroras 

 that occurred ; until after ten years, their records were 

 found both to give a fairly regular retrocession in 7 

 years from 100 down to 4; and the dates of these ex- 

 tremes to coincide, the first with the maximum, and the 

 second with the minimum, of the sun-spot cycle for the 

 time, as determined by other observers chiefly in Europe; 

 since which period the auroras have begun to increase 

 again ; thus, and the sun-spots too : 



Total Auroras 

 observed and 

 Year concluded. 



1870 1 08 Sun-spot max. 



1871 104 



1872 94 



1873 92 



1874 35 



1875 27 



1876 17 



1877 J 3 



1878 4 Sun-spot min. 



1879 16 



1880 22 



The recent researches of Baron Nordjenskiold, in his 

 famous Vega voyage, have shown more than ever that 

 the aurora is a pre-eminently terrestrial phenomenon, 

 having its seat actually half in and half out of the solid 

 earth. And yet the above numbers, so independently 

 observed in America, can be explained by nothing but 

 the frequency and intensity of the earth's auroral displays, 



