308 METEOROL'^GY AND ALLIED SUBJECTS 



(15) With reference to the relation between auroras and sun spots, the 

 author sums up the present state of our knowledge as follows : The 

 maxima of the sun spots accurately or very closely agree with the 

 quadratures of the planets Jupiter and Saturn. The differences are 

 smallest in those periods in which the spotted surface is greatest upon 

 the sun, when the auroras are the most frequent and most beautifully 

 developed, as in the years 1638, 1648, 1718, 1727, 1738, 1837, 1848. ^he 

 two longest periods (1660 to 1675 and 1789 to 1804) correspond to the 

 times of quadratures (1668 and 1797), for which times, according to the 

 previous observations, correspond no maxima. From these quadratures 

 of Jupiter and Saturn, Fritz computes again the greater aurora period as 

 55.56 years. 



(16) The eighth chapter deals with the relation between the aurora 

 and the electricity of the atmosphere and the earth. The electric nature 

 of the aurora is in general sufficiently well acknowledged, and some de- 

 tail of aurora phenomena can be reproduced in the electrical experiments 

 of our physical laboratories, but a satisfactory general theory as to the 

 exact explanation of the auroral phenomena has not yet been accom- 

 plished. 'No evidence of the existence of free electricity in the air was 

 observed in delicate experiments in the Arctic regions, made by Parry, 

 1819 to 1825, Fisher 1824, Franklin 1825 to 1827, McClintock 1857 to 

 1859, Bessels 187^, Nares 1875. But traces of electrical phenomena are 

 claimed to have been observed by Wyjkander at Spitzbergen, 1872 and 

 1873, and by Hjaltalin, in Iceland, and by Canton, in London. The 

 diurnal periodicity of atmospheric electricity, the annual periodicity, 

 and the secular periodicity have all been the subject of observation by 

 Schubler, Quetelet, Everett, Wisliczenus; but no definite relation be- 

 tween auroras and electricity can be deduced from these observations. 

 The relation between frequency of thunder storms and auroras has been 

 maintained by some; but the result announced by Von Bezold, namely, 

 that the maximum of auroras occurs at the time of the minimum of 

 thunder storms is directly controverted by Fritz, whose studies cover a 

 longer period and a larger number of stations, and demonstrate that 

 there is no definite relation between the two phenomena. On the other 

 hand, the relation between thunder storms and sun spots seems to be 

 more definite : at least Fritz finds that the maxima and minima of 

 thunder storms do not correspond to the maxima and minima of sun 

 spots. 



A further connection apparently exists between auroras and the dis- 

 turbances that are experienced on telegraph lines due to the so-called 

 earth currents. This phenomenon was first observed, 1848, by Matteuci 

 on the telegraph line between Pisa and Florence during the aurora of Oc- 

 tober 17, 1848; this phenomenon was also widely observed in Europe and 

 America during the great aurora that lasted from August 28 to September 

 2, 1859; other dates of equal or greater disturbance were 1869, May 13; 

 1870, April 5 and October 24 and 25; 1872, February 4; the observa- 



