1889. | VEEDER—ON THE AURORA, 21 
two years, as has been the case recently. The series of splendid auroras 
during the summer of 1886, and the magnificent double series during 
the winter of 1887-1888 exhibited an exact twenty-seven day periodicity 
entirely inconsistent with the idea that each outbreak was dependent 
upon a sudden developement of explosive energy alone. It is true that 
there are geysers in the Yellowstone Park and elsewhere that break 
forth with great regularity, but there can be no analogy to the case 
under consideration. Evenif outbreaks upon the 6un were geyser-like in 
their action, it would be necessary in order that this might become mani- 
fest in their earth-felt effects that their periodicity should invariably 
correspond closely to the time of the rotation of the sun, which is an 
altogether improbable assumption. 
It is evident, however, that the abruptness of beginning and peri- 
odicity of magnetic storms and auroras is not inconsistent, to say the 
least, with the supposition that they owe their origin to disturbances 
appearing by rotation at the sun’s eastern limb. Moreover the facts 
sustain this view. At times it has seemed as though outbreaks located 
elsewhere had been concerned, but by comparing the record during 
successive revolutions it has become apparent in many such cases that 
some small dot of faculz at the eastern limb was really responsible ; 
this mere dot at other returns developing into a disturbed area of vast 
extent, and being attended at each appearance for months by outbreaks 
of magnetic phenomena. Thus, judging the activity of disturbances by 
their history as well as their appearance, it has been found that there is 
a remarkable coincidence between the occurrence of auroras and the 
location of disturbances at the sun’s eastern limb. In order to make 
this evident it is necessary to have access to records made by instru- 
ments which record magnetic perturbations automatically. It may be 
shown also by reference to reports of auroras from an area sufficiently 
large to overcome the influence of local conditions, which, for reasons 
not as yet understood, often prevent auroral display. 
Employing the reports of the Signal Service Bureau it is found that 
during the three years from April 1886 to April 1889 there were one 
hundred and eighty-eight outbreaks of the aurora in the United States 
forming separate and well defined groups. In connection with one 
hundred and sixty-two of these observation of the sun was secured, and 
in every case a disturbance was found upon the sun’s eastern edge, 
small it is true in some instances, but larger at other returns so as to be 
unmistakable. There were twenty-two other instances in which out- 
breaks appeared by rotation, no aurora being reported. It is possible 
however that it was visible in these cases at more northerly latitudes. 
