NORTHERN LIGHTS. 807 



account of the preponderance of metal in the composition of that 

 body, generates positive electricity on the earth by induction, 

 while the negative electricity passes over into the atmosphere sur- 

 rounding the earth. The constitution of the air at different times 

 and at different places favors this process more or less. The con- 

 ducting metallic rod of our electrical experiments may be consid- 

 ered here as being replaced by mountain-peaks projecting high 

 into the air. 



If the equatorial currents, already mentioned by De la Rive, 

 are borne in mind, it is evident that the air at the poles must be 

 highly electrified, and that an exchange must then and there take 

 place between the negative electricity and the positive (induced) 

 electricity. This exchange gives rise to phenomena of light iden- 

 tical with those observed as northern lights at the north pole and 

 as southern lights at the south pole. 



This theory is strengthened by the observation that northern 

 lights are closely connected with the appearance of sun-spots and 

 protuberances on the sun. Already in former times a certain 

 periodicity of northern lights was noticed. Besides the annual 

 period in which they appear most frequently at the times of the 

 equinox, and least frequently at the times of the solstices, a period 

 of eleven years has been observed, corresponding closely to that 

 of the sun-spots, the maximum of which coincides with the maxi- 

 mum of northern lights. 



The appearance of sun-spots and protuberances, the connection 

 between which was pointed out by Tacchini in 1885, may be re- 

 garded as signs of changes occurring on the sun, probably involv- 

 ing increased combustion. 



This increased activity must influence the induced terrestrial 

 electricity, and in consequence also the phenomena of northern 

 lights. The variations and declinations of the magnetic needle, 

 moreover, give indubitable proof of the connection between 

 the periods of sun-spots and the electrical condition of the 

 earth. 



It should not seem strange that the terms electric and mag- 

 netic condition have been here used as synonymous. Since Oer- 

 sted's discovery of the influence of the electric current on the mag- 

 netic needle, and Ampere's theory of magnetism, electricity and 

 magnetism are regarded as merely two different forms of one and 

 the same force of nature. Translated for the Popular Science 

 Monthly from Ueber Land und Meet. 



Prof. Flower expressed the opinion, in his presidential address before the 

 British Association, that an impartial survey of the recent progress of paleonto- 

 logical discovery must lead to the conclusion that the evidence in favor of the 

 doctrine of a gradual transformation of living forms is steadily increasing. 



