428 THE CHEMISTRY OF THE SUN. [CHAP. 



The more profound the descent below the photosphere, the 

 more elongated will the spot system become by the receding of 

 the photosphere and the formation of vast ridges of faculse to 

 the westward. 



The fact of the great disturbances lying on the following 

 edge of a spot, was first pointed out by Messrs. De la Rue, 

 Stewart, and Loewy, and has been confirmed by the most recent 

 work of Spb'rer, who finds that the most rapid proper motions 

 always occur on the western side. These sometimes amount to 

 1,000 or 2,000 miles a day, and are most intense when the largest 

 spot- groups are formed, and slacken down after their formation} 

 Such groups tend, as Sporer has remarked, to extend along the 

 parallel of latitude they originate in. 2 



10. By the hypothesis the falls should be least at the poles and 

 at the equator. 



We have seen (in 8) that the atmosphere over the equator is 

 higher than it is over the poles. Working on this fact alone it 

 is clear that near the poles the particles will have a less, and 

 near the equator a greater, distance to fall than those in mid 

 latitudes. 



At the poles the velocity of the particles when they reach the 

 photosphere will be relatively small; near the equator, though 

 the velocity will be relatively great, the thickness of incan- 

 descent atmosphere to be traversed will be greater also. Both 

 these conditions are unfavourable to large disturbances of the 

 photosphere. 



Hence those particles and masses will be more effective which 

 fall neither at the poles nor at the equator; and in each 

 hemisphere N. and S. there should be a zone of latitude in 

 which the falls will be most effective. 



1 Nature, Nov. 1886, p. 72. 



2 PubUcationen, Potsdam, No. 1 (1878), p. 91 ; No. 5 (1880), p. 69. 



