THE SMITHSONIAN INSTITUTION. 13 



were viewed with wonder b}^ nearly all the existing generation. 

 Immediately after this great aurora, exhibitions of the phenomenon 

 became more frequent. From 1827 to 1848, 885 appearances of the 

 aurora are given in the records referred to by the author. Of these, 12 

 were of the first class, 45 of the second, 161 of the third, and 667 of the 

 fourth. 



The author places the middle of the period about 1837 ; and by sub- 

 tracting from this 65 years, he arrives at the middle of another visita- 

 tion. The duration of the period he considers to be a little more than 

 20 years. The middle of the next period of brilHancy, if this assump- 

 tion be correct, will be about the beginning of the next century. What- 

 ever may be the truth of this conclusion, the description of a large 

 number of auroras which he has collected, given either Irom the records 

 of others or irom his own observations, renders his communication 

 valuable. He does not adopt the hypothesis of the electrical origin of 

 this meteor, but considers it connected with the phenomena of the 

 zodiacal hght. The most conclusive proof, however, of the truth of 

 the former hypothesis is found in the fact of the disturbance of the 

 magnetic needle, when dehcately suspended, during the appearance of 

 the aurora, and the actual transmission of currents of electricity along 

 the hnes of telegraphs which extend in a north and south direction. 

 The last fact has been reported separately to us by different individ- 

 uals belonging to the Smithsonian corps of observers. 



Though no complete explanation has been given of all the facts of 

 the aurora, yet the most plausible hypothesis is that which attributes 

 the phenomena to electricity generated principally in the torrid zone by 

 evaporation. By this process the earth is rendered negative, and the 

 vapor which ascends into the upper atmosphere highly positive. It is 

 thence transferred towards the poles by the return trade winds, and 

 descends to the earth to restore the equilibrium. A current of elec- 

 tricity is thus constantly passing from the poles to the equator during 

 the appearance of the aurora; and hence, according to this view, the 

 disturbance of the needle. 



As an appendix to this paper, Peter Force, esq., of this city, has pre- 

 sented to the Institution an extended series of notices of the aurora 

 collected from all the publications in which they occur, from about 1827 

 to the present year, arranged in order of time and of latitude. This will be 

 a valuable contribution of facts towards a definite determination of the 

 law and physical cause of these mysterious meteorological phenomena. 



It would scarcely be comphmentary to the general intelligence of the 

 public of the United States, if I were again to attempt to vindicate the 

 importance of investigations like that of the aurora ; and it ma}?" be a 

 sufficient answer to those who would question it, to say that they are 

 such as particularly occupied the attention of vSmithson himself, and 

 that they mUst, consequently, be included as a part of that knowledge 

 which it was the intention of his bequest to increase and diffuse among men. 



4. The next paper is on the Tangencies of circles and spheres, by 

 Major B. Alvord, of the United States army. It consists in the solution 

 of a series of problems which have at different times exercised the 

 ingenuity and skill of the geometer. It was referred separately for 

 examination to Professor Lewis R. Gibbes, of Charleston, South 



