sii PR E I' A CE 



of notices of the aurora in the voyages of Arctic explorations by Peter Force, Esq., 

 of Washington; published in Vol. VIII. of Smithsonian Contributions (in 1856), 

 ely, " that on the Atlantic Ocean, and other open water, the aurora is most fre- 

 quent and most brilliant." These facts would appear to favor the hypothesis that 

 auroral displays an 1 due to electrical discharges between the air and the earth, since 

 such discharges would, at least in part, l>o interrupted by a stratum of* non- 

 ducting ice. 



The accompanying map, to illustrate the voyage of the Fox, is drawn by Mr. 

 Schott on the plan of the projection known as the polyconie, which is a develop- 

 ment of the earth's surface on cones tangent to each parallel of latitude ; the radius 

 being the distance between the arc of the parallel and the earth's axis. 



Points of intersection of the parallels and the meridians are, according to Mr. 

 S( hott, readily computed by substitution in the following formula?, in which as and 

 ii are the co-ordinates for any difference of longitude, v, on any parallel of latitude. 

 L, and A the normal ending at the polar axis. 



x = N cos L (» — " sin 2 L + . . .) 



if = iV cos L ("" sin L — '"_ sin* L + . . .) 



This projection is used in the Hinted States Coast Survey, and is described in 

 the Report of the Superintendent, Dr. Bachc, for 185{), Appendix, 33. 



Smithsonian [nstitution, 



Washington, December, 1 *('.•_' 



JOSEPH HENRY, 



Si i retary S. I. 



