138 ROCHESTER ACADEMY OF SCIENCE. [^^ay 9, 



should be related in some way to auroras which also are of electrical 

 origin. This e.xpectation has been realized by the discovery that 

 hunderstorms not unfrequently take the place of auroras in the reg- 

 ular order of recurrence. There seems to be a substitutive or recip- 

 rocal relation between these two classes of phenomena, the one taking 

 the place of the other, wholly or in part, under conditions now in 

 process of investigation, and with reference to whose study the pres- 

 ent paper is essentially a report of progress. 



Evidence has been secured which indicates that thunderstorms 

 prevail most widely when disturbed areas are at the sun's eastern limb, 

 and at a distance from the plane of the earth's orbit, thus differing 

 from auroras in whose case, proximity to that plane appears to be 

 essential. This difference in the location of the originating disturb- 

 ance appears to modify the method of conduction of the electrical 

 impulses, the earth in the one case being in exact range with lines uf 

 force and conducting medium experiences the species of impulse 

 known as magnetic, and in the other case being somewhat out of range 

 encounters instead disruptive discharges which fall at points where 

 the attendant terrestrial conditions are most favorable. 



There are resemblances between the behaviour of thunder- 

 storms and auroras consistent with such community of origin. Both 

 occur in well defined belts which undergo charges of latitude in cor- 

 responding cycles of about eleven years duration, and are concentric 

 with the magnetic poles of the earth rather than with the axis of 

 rotation, thus corresponding to a like arrangement of belts of equal 

 atmospheric pressure. Both exhibit daily maxima and secondary 

 maxima at certain hours of local time, depending upon concentration 

 of effect at points which maintain a fixed position with respect to the 

 source of induction but which are movable with respect to the earth 

 itself. In the case of thunderstorms the chief maximum is in the 

 afternoon and the secondary maximum between midnight and morn- 

 ing, even hail as well as thunder and lightning having been known to 

 occur during the night. The corresponding maxima of auroras fall 

 in the evening and early morning. Accordingly when an aurora in 

 the eastern hemisphere is coincident with thunderstorms in the west- 

 ern and vice-versa, the substitution may depend in part at least upon 

 this relation to certain hours of local time, as well as upon differences 

 in respect to the humidity of the atmosphere and the like, affecting 

 its conductivity. The system of concerted observation organized by 

 the writer in which a large number of observers are participating has 

 revealed a tendency to the localization of the aurora somewhat sim- 



