METEOROLOGY. 



369 



sion is to be determined. For these observations he proposes a binoc- 

 uhir attached to a circle having a horizontal axis which revolves around 

 a vertical axis, so that the binocular can have the plane of its axes 

 brought into the plane of the auroral beams. Many observations show 

 that the auroral rays arrange themselves pre eminently along the mag- 

 netic parallels in curves that cut the magnetic meridians at right angles; 

 they also show that the auroral phenomena as arranged along the mag- 

 netic i)arallels follow the curves of equal total magnetic intensity. [Z. 

 0. G. J/., XIX, p. 405.) 



358. Dr. H. Ekama, of Haarlem, gives a summary of the observations 

 on the aurora made by the International Polar party sent by the gov- 

 ernment of the Netherlands to the Sea of Kara. The aurora was in 

 general very unsteady and variable, so that drawings could rarely be 

 made. Arcs frequently occurred, but soon changed to the form of 

 bands ; the dark band below the arc was never distinctly seen. The 

 aurora was invariably visible when the heavens were clear and the moon 

 not too bright; the finest appearances occurred at about 10.30 p. m., 

 when the corona most frequently occurred ; the bands were strongest 

 about 9.30 p. m. The auroras were generally on the north side of the 

 heavens, and only reached to the south of the zenith after a very bright 

 display; the highest point of the arcs did not lie in the magnetic gra- 

 dient, but in the astronomical meridian. Out of 86 observed arcs and 

 66 bands the summits of 64 and 41, resi^ectively, lay in the astronomical 

 meridian. Ekama has computed the altitude of his auroras by the for- 

 mula given by Mordenskiold in his account of the Vega's wintering in 

 Behring's Sound, 1878-'79; the results of nine nights agree closely, and 

 give for the distance of the arc above the earth's surface 0.033 of the 

 earth's radius; for the radius of the nearly horizontal arc itself 0.034; 

 and for the distance of the center of this circle below the earth's surface 

 0.02 of the earth's radius, which value agrees with that of Kordenskiold. 

 The auroras were generally very faint ; the arcs had no color. The wave 

 length of the peculiar auroral line was determined by the spectroscope 

 at 550.53 millionths of a millimeter; no other lines were visible; even 

 a wholly red aurora gave only this yellow-green line. No connection 

 was found between the polar bands of clouds and the auroral light. Out 

 of 203 polar bauds the vanishing or converging points were distributed 

 as follows : 



The direction of the polar bands probably depends on the direction 

 of the wind prevailing at the cloud level. {Z. 0. G. ilf., xix, p. 482.) 

 S. Mis. 33 24 



