Show DISPLAY THAT IS PERIODIC PAu aurora rora borealis Bo realia has its manifestations at intervals of prom from ten to sixty years the name aurora borealis bore alls was borst used by Cas who 1 in 1021 observed one in france and vi wrote u a a description of it the aurora is periodic in its manifestations the finest displays being at intervals ot of 00 10 years and less marked ones at intervals of 10 or 11 ears it is asserted that the greater and lesser displays correspond with the increase and decrease of spots on the lun this phenomenon Is generally manifested in the following way Iray A I dim light appears on the horizon shortly after twilight and gradually the shape of an arch having I 1 pale yellow color with its concave olde turned earthward from tills this jerch ach streams of light shoot f orth forth passing air from yellow to green and then to kril llant violet the name aurora borealis bore alls while rene generally rally referring to the 1 northern or thern lights Is applied to a similar phe hot nenon visible in the vicinity ot of the oth pole |