Solar Changes of Temperature and Variations in Rainfall. 413 



lines of iron can be seen revealing themselves as the number of un- 

 known lines increases. 



We are, therefore, quite justified in assuming a very great increase 

 of temperature at the sunspot maximum when the "unknown" lines 

 appear alone. 



The curves of the "known" and " unknown " lines have been ob- 

 tained by determining for each quarter of a year the percentage 

 number of known and unknown lines and plotting these percentages 

 as ordinates, and the time elements as abscissae. Instead of using the 

 mean curves for all the known elements involved, that for iron is em 

 ployed, as it is a good representative of " known " elements, and has 

 been best studied. When such curves have been drawn they cross 

 each other at points where the percentage of unknown lines is 

 increasing, and that of the iron or known lines are diminishing, or 

 vice versa. 



We seem, therefore, to be brought into the presence of three well- 

 marked stages of solar temperature. 



When the curves of known and unknown lines cross each other, that 

 is, when the number of known and unknown lines is about equal, we 

 must assume a mean condition of solar temperature. When the un- 

 known lines reach their maximum we have indicated to us a + pulse 

 or condition of temperature. When the known lines reach their maxi- 

 mum we have a - pulse or condition of temperature. 



The earliest discussion showed that, generally speaking, the un- 

 known-lines curve varied directly, and the iron-lines curve varied 

 inversely with the spot-area curve. The curves now obtained for the 

 whole period of twenty years not only entirely endorse this conclusion, 

 but enable more minute comparisons to be drawn. 



The " widened line " curves are quite different from those furnished 

 by the sunspots. Ascents and descents are both equally sharp, changes 

 are sudden, and the curves are relatively flat at top and bottom. The 

 crossings are sharply marked. 



During the period since 1879 three such crossings have occurred, in- 

 ! dicating the presence of mean solar temperature conditions, in the 

 I years 1881, 1886-7,* and 1892. It was expected that another crossing 

 I with the known lines on the rise would have occurred in 1897, indi- 

 I eating thereby the arrival of another mean condition of solar tempera- 

 ture, but as yet no such crossing has taken place. 



The following tabular statement shows the years of those crossings, 

 | together with the probable dates, in brackets, of the two previous 

 I crossings, as determined by the time of occurrence of the preceding 

 sun-spot maximum. 



* According to the observations tbe mean wa: reac-hed in December, 18S6, or 

 January, 1887. 



