134 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



cloudy weather, moonli^lit nights and the different lengths of daylight in summer 

 and winter. But the ditferences are noticeable too, and afford another proof of 

 the statement I ventured to make last session that the extent of spotted areas on the 

 sun is not an exact measure of solar activity. Counting the same spot over and 

 over again, day after day, as it persists, is in my judgment erroneous, being a 

 duplication and reduplication of the credit entry in the solar ledger, whereas the 

 magnets on the earth rarely show continuing storms for more than a couple of days. 

 The auroral curve corresponds more closely to the magnetic curve than to the one 

 showing the spotted areas on the sun. 



Professor Wolfer, on being informed of this view, which implies that the 

 special solar energy concerned in the production of a sun-spot does not last 

 throughout its visibility, but is greatest at the outburstiug of the spot and during 

 its active growth, and diminishes with the decay of the spot, replied that he be- 

 lieved the force which caused the spot continued until its extinction, but later 

 letters show less confidence in that theory. The general question of sun-activity 

 is of the greatest interest and importance. 



Galileo and Scheiner were the first observers of sun-spots early in the seven- 

 teenth century, but it was not until the middle of the nineteenth that Schwabe 

 discovered their recurrent frequency in what is known as their eleven year period. 

 The systematic observation of faculse comes quite within our own times, as does 

 that of prominences, which, indeed, could only be recorded after one of the most 

 wonderful of the maoy applications of the spectrescope had enabled us to see them 

 as they come on or pass off the sun's limb or edge. These three forms of solar 

 activity are necessarily related, that is, while the spots are at a maximum, there 

 are more faculte and prominences, but the precise times do not correspond. So 

 magnetic energy on the earth follows very closely the sun-spot curve, and, as 

 might be expected, auroral frequency does the same. But, as compared with sun- 

 spots, magnetic storms tend to "lag." The principal magnetic disturbance is 

 usually a few hours after the centrality of the spot region from which the excess 

 over the daily issue of radiations issues, sometimes even a day or two. Also, 

 curious to note, these Tromholt auroral curves show a usual "lag" of months 

 between the auroral and the sun-spot manifestations. The figures work out, by 

 my calculation, as follows : — 



Minima. 

 By Smi-spots. By Auroraj. 



Average lag, .55 of a year. Average lag, .24 of a year. 



The determination of the auroral maxima and minima to the fraction of a 

 year is not so precise as that of sun-spots has become, owing to the lack of obser- 

 vations in both hemispheres and all arouud the earth. We see no aurorte in the 

 far north in May, June, July and August, and have as yet no reliable means of 

 rectifying the irregularity by observations in the far south. 



We see in the Tromholt curve, and it is not unimportant to observe, that the 

 wave between the principal auroral maxima appears to embrace two spot maxima. 

 Thus, the great curves from 1755 to 1776, and from 1776 to 1779, seem each to be 

 one wave of influence having two impulses about eleven years apart. So also the 

 quiet time from 1799 to 1823.5 seems one period, while from 1823.5 to 1845.5 is 

 evidently one wave of twenty years length. While from 1845.5 to 1856 is a shorter 

 vibration, it is manifest that from 1856 to 1879 we have the double period again. 

 I have not yet been able with the data at control to prolong the Schroter tables to 

 the present date, for the auroral data on this side of the Atlantic, which are being 



