PHENOMENA MANIFESTED IN TELEGRAPHIC LINES, ETC. 303 



of the above view, Professor Olmstead cites many facts iu a learned 

 essay, published iu the contributions of the Smithsonian Institution of 

 America. Mr. Tarry also has noted a similar fact in the great aurora of 

 February 4, 1872, while comparing the times in which the luminous phe- 

 nomena were seen in Europe with the times in which they were seen in 

 Duxbury, near Boston.* 



To this I can add that the Italian consul of Cyprus addressed a letter 

 to his excellency our minister of foreign affairs, which was kindly com- 

 municated to me, from which it appears that the luminous i)heuomena 

 of the aurora of February 4 last were very conspicuous at Cyprus, that 

 they became feebler toward 10 o'clock, (local time,) and after that disap- 

 peared almost entirely. At Paris, also, the luminous i)heuomena of the 

 same aurora were very vivid till 10 o'clock, (local time,) then became 

 much weaker, and disappeared almost entirely. Now, as Cyprus is about 

 two hours east of Paris, it follows that in absolute time the luminous 

 phenomena of the aurora ceased at Cyprus two hours before they dis- 

 appeared iu Paris. If it were not so, and the light of the aurora borealis 

 had been very bright at Cyprus at the same time that it appeared very 

 splendid in Paris, instead of beginning to decrease in the latter place 

 at 10 o'clock without any further increase of brightness, it ought to have 

 continued in its splendor till after midnight. 



Now, how can we explain the fact that the luminous phenomena of 

 the aurora borealis appear first in the east and after in the west ? The 

 theory that the aurora is nothing else but a slow electrical discharge, 

 which takes place between the upper and the lower strata of our atmos- 

 phere, is well known, generally admitted, and confirmed by the beauti- 

 ful experiments of De La Eive. On this point there can be very little 

 doubt at present. But is this a complete explanation ; tbat is, does it 

 give a reason for all the circumstances which accompany the aurora bo- 

 realis? Besides the circumstance that the luminous i^henomena of the 

 aurora move, so to speak, from east to west, there is another very im- 

 portant one which must not be overlooked when we are seeking for an 

 explanation of these phenomena as satisfactory as we can obtain. The 

 late researches made by Professor Loomis prove that in latitudes which 

 are not very high the number of auroras and their luminous intensity 

 has a maximum and a minimum about every ten years ; and this fact is 

 also confirmed by an examiuation which I have undertaken of an ex- 

 tensive series of observations existing in this observatory, in which the 

 exhibitions of auroras are accurately recorded. Although the theory 

 which regards the aurora borealis as the result of slow and prolonged 

 discharges of electricity is physically complete, and explains fully the 

 electrical and luminous phenomena, it does not seem of itself to give 

 a satisfactory reason either for the periodicity of the auroras or of 

 the successive progress of the phenomena from east to west. That the- 



* Deuison Olmstead, Smithsonian Contributions January, 1655, pp. 44-45 ; H. Tarry, 

 Comptes-rcndus, Vol. LXXIV, p. 549. 



