A NEW METHOD OF RESEARCH. 



i7 



that the calcium vapor usually coincides closely in form and position 

 with the lamia', and hence the calcium clouds were Long spoken of 

 under tin's name. In the new work at the Yerkes Observatory the 

 distinction between the calcium clouds and the underlying faculge is so 

 marked that a distinctive name for the vaporous clouds has become 

 necessary. They have therefore been designated floccn/i. a name chosen 

 without reference to their actual nature, hut suggested by the floc- 

 culent appearance of the photographs. 



In order to analyze these lloeeuli and to determine their true struc- 

 ture, a method was desired which would permit sections of them at 

 different heights above the photosphere to he cut off, as it were, and 



// K 



Fig. S.— i^AND A'Lines in Electric Arc, showing Revej^als. 



photographed. Fortunately there is a simple means of accomplishing 

 this apparently difficult object. At the base of the flocculi the calcium 

 vapor, just rising from the sun's interior, is comparatively dense. As it 

 passes upward through the flocculi it reaches a region of much lower 

 pressure, and during the ascent it might he expected to expand and 

 therefore to become less dense. Now we know from experiments in 

 the laboratory that dense calcium vapor produces very broad spectral 

 bands, and that as the density of the vapor is decreased these bands 

 narrow down into fine sharp lines (Fig. 8). An examination of the 

 solar spectrum will show that the // and A' lines of calcium give evi- 

 dence of the occurrence of this substance under widely different densi- 

 ties in the sun. The broad dark bands, which for convenience we 

 designate as H x and K 1} are due to the low-lying dense calcium vapor 

 (Fig. 1). At their middle points (over flocculi) are seen two bright 

 vol. lxv. — 2. 



