"44 MEMOIRS OF THE AMERICAN ACADEMY. 



Is it proved, as yet, that years of sun-spots are years of auroras any more satisfac- 

 torily than the theory is proved that years of fire-balls are years of sun-spots, as Ritter 

 suggested, 1 or the theory that years of earthquakes are years of auroras ? A lesson 

 of caution against hasty conclusions on subjects of such complexity may be drawn 

 from the fact, that whereas Boue 2 favored the conclusion that the aurora goes hand in 

 hand with the earthquake, and whereas Wolf had decided, though from data afterwards 

 acknowledged to be insufficient, that years rich in sun-spots corresponded to years rich 

 in earthquakes, Kluge, 3 from a more searching examination and the use of larger 

 materials, finds a periodicity for earthquakes as long as that which governs the sun- 

 spots and magnetic disturbances, but with maxima and minima reversed. 



Fritz 4 has recently investigated the periodicity of tbe aurora in relation to the 

 frequency of lightning, and of the precipitation of rain or snow, and the amount of 

 the fall, and comes to the following conclusion : — 



" Obige Zusammenstellungen ergeben uns somit das Resultat, class weder in Bezug auf den 

 Wechsel der jahrlich beobachteten Anzahl Gewitter fur wenige oder viele tiber die Erde verbreite- 

 ter Orte, noch fur die in ahnlicber Zusammenstellung untersuehten Mengen von Niederschliigen, 

 sich irgend ein regelmiissiger periodiscber Wechsel zu erkennen gibt, am wenigsten ein solcher, 

 welcher in der Weise mit der Haufigkeit der Polarlichter barmonirt, dass man auf irgend welche 

 Wecbselbeziehung zwischen den ersten beiden Erscheinungen einerseits und den Polarlichtern 

 andrerseits scbliessen konnte. Obige Zusammenstellungen zeigen recht deutlicb, wie wenig zuliissig 

 Schliisse in der Meteorologie sind, die aus einzelnen Beobachtungen gezogen werden, wie dieses bei 

 der grossen Nordlichtperiode von 1859 beziiglich der vorbergehenden Jahre geschehen." 



Some importance has been attached to the supposed resemblance between the solar 

 corona, the zodiacal light, and the aurora, when they are examined through the spec- 

 troscope, as proving an identity of nature in the phenomena. Such an identity, if fully 

 established, would prove nothing more than this : that there existed in the earth's 

 atmosphere, or in whatever other region of space might be the scene of auroral mani- 

 festations, the same materials as pervaded the luminous atmosphere of the sun. That 

 the sun had any influence in setting them on fire, and that there was any connection 

 between their incandescence and the fluctuations in the sun's light or heat, would 

 require the same proof as ever. Moreover, the observations made on the aurora with 

 the spectroscope utter an uncertain sound. Angstrom finds this spectrum discontinu- 

 ous, whereas Winlock observes in it, at least in that of the eastern and western arch 

 of the aurora, perfect continuity. 



1 Gilbert. Annalen der Physik, XVI. 221. 



' Sitzungsberichte der Kais. Acad, der Wissensch. XXII. 435. 



* Vierteljahrsschrift der Xaturforsch. Gesellschaft in Zurich, IX. 267. 



' Vierteljahrsschrift der Naturforsch. Gesellschaft in Zurich. XIII. 369. 



