THE SUN AND SUNSPOTS MAUNDER 163 



continuous. It always starts from high latitude ; when it has reached 

 low latitudes it is cut off; there is no gradual return to the high 

 latitudes. The reappearance of spots in high latitudes is sudden. 



There are now three facts before us. There is one solar cycle, 

 shown differently, in time and form of the curve, in the two hemi- 

 spheres, and now in two manifestations of quite separate character; 

 one in area, a complete pulsation, and one in latitude, which moves 

 in one direction only; i. e., from high solar latitudes to low. 



The fourth illustration (fig. 4) appeared in the Monthly Notices, 

 74, Plate 2, between pages 114 and 115. It deals only with the 

 distribution of spots in latitude, nothing being shown concerning the 

 areas of spots. The materials are drawn entirely from the Green- 

 wich Photoheliographic Results, and extend over the years 1874-1913. 

 Seven thousand spots are represented, but the short straight line 

 which indicates the latitude of a spot is drawn just as long and 

 as heavy for a small spot as for a large one; for one spot as for a 

 dozen. All spots occurring during the same rotation of the sun are 

 represented in the same vertical line. The diagram is concerned 

 only with the distribution of spot centers in heliographic latitude. 



This diagram has been familiarly called " the butterfly diagram," 

 as it seems to suggest three butterflies pinned down to a board with 

 their wings extended. Heads, bodies, and legs have disappeared, 

 but the outstretched wings remain. Each pair of wings is distinct 

 from the next; there is a clear V-shaped gap between each of the 

 three specimens. Here again the first deduction is reinforced from 

 an altogether different set of facts. The solar cycle is one. 



This diagram further suggests that the origin of the solar spots 

 lies within the sun, not without. They come from below the sur- 

 face; they are not impressed upon the surface by some exterior 

 influence; neither by planets nor by meteors. No exterior influence 

 could invariably begin a fresh disturbance in a high latitude simul- 

 taneously on both sides of the Equator. 



If we take a card with a narrow slit in it, parallel to the sun's 

 equator, and move it up and down over the diagram, then, wherever 

 that slit is placed within the range of the sun-spot zones, the three 

 sun-spot cycles will be brought out clearly and unmistakably. Our 

 first conclusion, that the sun-spot cycle is one, is now extended ; it is 

 true not merely for sunspots in general, but for the spots of any 

 special zone in particular. This conclusion goes deeper than our first, 

 which was merely that the sun-spot cycle, on the average, lasted for 

 about lli/> years. The sun as a whole is under the law of that cycle, 

 and erfch individual zone has its own particular part to play in it. 

 But the sun as a whole is a unit, no matter how distinct its dichotomy 

 into two hemispheres, no matter how distinct may be the action in 

 any particular zone. 



