•284 PROFESSOR C. PIAZZI SMYTH ON 



smaller, outburst of energy in the course of the longer dying out of the principal wave ; 

 sometimes single as in our first, and probably in the third, wave ; sometimes double as 

 in the second. 



But while the first of these three particular waves has nearly the normal steepness of 

 front, viz. 4 years of rise to 7 years of fall, and a maximum height of 220 groups ; the 

 second of our three waves, rushes up in the short period of only 3 years, and then to the 

 unparalleled height of 280 groups, but takes 8 years to decline therefrom. While the 

 third wave is feeble and sluggish beyond example, employing 5 and a half years to 

 rise slowly to its maximum, and that a poor one of only 160 groups. 



Taking all these features then of Solar variation itself into account, no one need be 

 surprised at finding on the earth less Barometric monthly range in the days of the third 

 Sun-spot cycle, than in the two earlier ones. Or, that in the times of the second Sun-spot 

 cycle, the Maximum Barometric range on the earth shot up in the same excessive 

 manner, and simultaneously with the Sun-spot curve's then most exaggerated effort ! ! ! 



9. Aurora, Lightning, and Sun-Spots. 



In fact the variations inter se of the three Sun-spot cycles which cover the duration 

 of all the Scottish Society's Meteorological Observations, — though entailing such alterations 

 of weather-phenomena from one to the other, as to have caused some persons very need- 

 lessly to lose their faith in any connection, — are a most fortunate feature to assist in the 

 present investigation; and we have not to go much further in our research before alight- 

 ing on another Meteorological curve which intensifies, while it synchronises with, the 

 excess and acuteness of the energy- outburst displayed in the second Sun-spot curve ; and 

 equally confirms the deplorable defect of energy revealed in the third one. 



This singularly confirming curve is that of Aurora, its frequency and extent; or 

 the number of times seen, and the number of stations reporting it each time. 



There can hardly be, it will be confessed on examining the Plates, anything more 

 excessive and vivid in intensity than the Aurora returns during the second sun-spot 

 cycle ; or more tame, flat, and miserable than during the third. While if the first spot 

 cycle is not very conspicuously marked with Aurora, it is largely from the Aurora obser- 

 vations not having been begun so early as the other items of Meteorology, and having 

 therefore lost the critical epoch of the beginning of that cycle. 



Further, the " Strength of the Wind " curve, responds sensibly, though inversely to 

 the Auroral curve. So that during years of abundant Aurora display, the winds were 

 moderate in force, and chiefly from the West. But when Auroras left us in darkness, the 

 winds became more violent and verged to East and North. 



But there is a more accentuated connection still, though by opposition, between 

 Aurora and Lightning. The very maximum demonstration of all the Aurora being 

 absolutely coincident in time, with the very minimum of Lightning, and vice versa; 

 or that when Lightning is up, Aurora is down; yet they are both thought to be of an 

 electrical nature. 



