358 



Mr. J. N. Lockyer. On the 



[May 6, 



spots, and therefore again there will be no prominences. Such was 

 the state of things on the southern surface of the ring from December, 

 1877, to April, 1879, during which period there was not a single spot 

 observed the umbra of which was over 15-millionths of the sun's 

 visible hemisphere. 



Assume a disturbance. This may arise from collisions, and these 

 collisions would be most likely to happen among the particles where 

 the surface of the ring meets the current from the poles. These 

 particles will fall towards the sun, thereby disturbing and arresting 

 the motion of other particles nearer the photosphere, and finally they 

 will descend with a crash on to the photosphere, from that point where 

 the surface of the ring enters the atmosphere, some distance further 

 down. 



The American photographs in 1878 supply us with ample evidence 

 that this will be somewhere about latitude 30°, and here alone will 

 the first spots be formed for two reasons. 



(1.) In the central plane of the ring over the equator, the particles 

 will be more numerous, a rapid descent, therefore, in this central 

 plane will be impossible, for the reason that the condensed matter 

 has to fall perhaps a million of miles through strata of increasing 

 temperature ; there will, therefore, be no spots ; and practically 

 speaking, as is known, there are no spots at the equator, though 

 there are many small spots without umbrae between latitudes 3° and 

 6° K and S. 



Above latitude 30°, as a rule, we have no spots, because there is no 

 ring, and further the atmosphere is of lower elevation, so that there is 

 not sufficient height of fall to give the velocities required to bring 

 down the material in the solid form. 



The lower corona where the corona is high, and it is highest over 

 the equator, acts as a shield or buffer, volatilisation and dissociation 

 take place at higher levels. Where this occurs, spots are replaced 

 by a gentle rain of fine particles slowly descending, instead of the 

 fall of mighty masses and large quantities of solid and liquid 

 material. 



Volatilisation will take place gradually during the descent, and at 

 the utmost only a veiled spot will be produced. 



We know that when the solar forces are weak, such a descent is 

 taking place all over the sun, because at that time the spectrum of the 

 corona, instead of being chiefly that of hydrogen, is one of a most 

 complex nature, so complex that before 1882 it was regarded by 

 everybody as a pare continuous spectrum, such as is given by the 

 limelight. 



The moment the fall of spot material begins we get the return 

 current in the shape of active metallic prominences, and the produc- 

 tion of cones and horns which probably represent the highest states of 



