444 THE CHEMISTRY OF THE SUN. [CHAP. 



In 1871 in India and in 1882 in Egypt, both maximum years, 

 I did not see half a dozen on either occasion, a very striking 

 fact, and one not explained by the varying duration of totality. 

 Of course the longer the totality, the more is the coronal light 

 as well as the photospheric light prevented from reaching the 

 atmosphere. 



17. By the hypothesis the solar radiation will lie greatest when 

 the numler of falls is greatest. 



It is a result of observation that from the time of the first 

 falls in a latitude above 30, down to the end of the cycle in 

 latitude 6 or 8, a period of something like thirteen or fourteen 

 years elapses. If this solar cycle depends upon an influence 

 from without, this external influence must therefore have a 

 period of variation of thirteen or fourteen years. But the period 

 effective in producing changes in the amount of solar radiation 

 to such a body as the earth, must depend, if the changes exist, 

 upon the time which elapses between successive maxima, that 

 is, about eleven years. 



In considering this question of radiation it must be borne in 

 mind, that the more the excess radiation is localised, as, say in 

 the spot zones, the more effective it will be ; as the smaller the 

 radiating area of high intensity is, the less absorption will be 

 experienced in the solar atmosphere. 



That the effects of such variations in the amount of energy 

 radiated to the Earth have already been traced in various 

 branches of magnetical and meteorological science, is by some 

 still considered doubtful. This matter, however, is one of 

 such high practical importance that solar physics in their 

 entirety would be worth investigating if more light on this 

 point only were the sole result that might be anticipated. 



It is now time to sum up this chapter. It will have been 

 seen that the idea of dissociation is not out of harmony with 

 any known solar phenomena, and that its introduction renders 



