PROCEEDINGS ROCHESTER ACADEMY OF SCIENCE. Vov. I. 
BEATE 212: 
Tas_e SHOWING PERIODICITY IN OCCURRENCE OF AURORAS. 
The accompanying table has been constructed by counting the stations, reporting 
auroras each day in the Monthly Weather Review of the United States Signal Service, and 
arranging the numbers thus obtained in periods of twenty-seven days six hours and forty 
minutes. The six hours, or one-quarter day, is provided for by adding a day to each 
fourth period, and the forty minutes, or one-thirty-sixth, day by adding a day to each 
thirty-sixth period. The grouping together of larger numbers indicates increased preva- 
lence of the aurora at this interval, which corresponds to the time of a synodic revolution 
of the sun. Annual interruptions of such series of recurrences are also apparent. (See 
columns 4 to 10 and 18 to 24). 
