A. MATHEMATICS AND ASTRONOMY. 47 



and such as to sii2:2:est that the connection between mage- 

 netic and auroral curves is more intimate than between the 

 auroral and the sun's spot curves. The critical periods of 

 the auroral curve occur a little later than those of the sun's 

 spot curve, and the aurora maximum is frequently more pro- 

 longed than the sun spot maximum. If we institute a com- 

 parison between the auroral and the magnetic curve, we 

 shall find the correspondence to be still more remarkable. 

 The auroral maximum generally occurs a little later than the 

 magnetic maximum, while the time of auroral minimum co- 

 incides with and slightly precedes the magnetic minimum. 

 On the whole there seems to be no room for question that 

 the number of auroras seen in the middle latitudes of Europe 

 and America exhibits a true periodicity, following very close- 

 ly the magnetic periods, but not exactly copying them. If, 

 now, we inquire as to the proper connection between these 

 three classes of phenomena, we can not suppose that the 

 small black spot on the sun exerts any direct influence on 

 the earth's magnetism or electricity, but we must rather con- 

 clude that the black spot is the result of a disturbance at the 

 sun's centre, that is accompanied by an emanation of some 

 influence from the sun which is almost immediately felt upon 

 the earth in an unusual disturbance of the earth's mascnetism 

 and development of the auroral light. "Appearances," says 

 Professor Looniis, "favor the idea that this emanation con- 

 sists of a direct flow of electricity from the sun. If we main- 

 tain that lio'ht and heat are the resiilt of vibrations of a rare 



CD 



ether which fills all space, the analogy between this and 

 electricity would lead us to conclude that this latter is also 

 the result of vibrations in the same medium, or, at least, that 

 it is a force capable of being propagated through the ether, 

 with a velocity similar to that of light." This idea of the 

 nature of electricity has already been developed by other 

 scientists, especially by J. Clerk Maxwell. 4 D, 1873, 245. 



ON THE COXXECTIOX BETWEEN AUEORAS, SUN SPOTS, AND 



TEEEESTEIAL MAGNETIS:\r. 



Dr. H. Fritz has recently published the results of an in- 

 vestigation on the periodicity of the auroras, and his con- 

 clusions are not very dissimilar to those subsequently pub- 

 lished by Professor Loomis, of Yale College. Fritz says that 



