430 THE CHEMISTRY OF THE SUN. [CHAP. 



13. By the hypothesis, if the falls continue, and vary their 

 latitude, constantly increasing or diminishing it, this can only 

 happen because currents either from the equator in one case or 

 from the poles in the other, are acting upon the exterior layers of 

 condensed and condensing material. 



As a matter of fact the spots from the minimum period 

 decrease their latitude. This is undoubted, and rests upon 

 the observations of Carrington and Sporer; it is also amply 

 confirmed by the Kew and Greenwich reductions of solar 

 photographs. 



The accompanying curves, which bring together the results of 

 Sporer's observations from 1854 to 1880, show the latitudes of 



FIG. 126. Sporer's curve of the change in the latitudes of sun-spots. Two 

 cycles are shown, the first begins in a high latitude, and the latitudes are 

 constantly reduced till it ceases. A second cycle begins in a high latitude 

 before the first ceases in a low one. 



the spots observed in each hemisphere (they were mainly the same 

 in both) in each year. It will be seen that in that period there 

 were two series of spots. The first beginning in 1856 and 

 extending with constantly decreasing latitude till 1868, and the 

 second beginning in 1866 and lasting till 1880. We learn 

 from this that the true sun-spot cycle is one extending over 

 twelve or fourteen years, and that another begins in high 

 latitudes before the former one has ceased. 



