2o POPULAR SCIENCE MONTHLY. 



progress. The vapor, rendered highly luminous by intense heat or 

 other causes, is shot out from the sun's interior with great velocity. 

 Consequently there are rapid changes in the forms of these brilliant 

 regions, whereas the more extensive flocculi, which occupy the greater 

 part of the photograph, change slowly, and represent a much less 

 highly disturbed condition of affairs. The brilliant eruptive flocculi 

 always occur in active regions of the solar surface, and doubtless cor- 

 respond with the eruptive prominences sometimes photographed pro- 

 jecting from the sun's limb. A remarkable instance was recorded on 

 the Kenwood photographs, which showed four successive stages in an 

 eruption of calcium vapor on an enormous scale. A vast cloud thrown 

 out from the sun's interior completely blotted from view a large sun- 

 spot, and spread out in a few minutes so as to cover an area of four 

 hundred millions of square miles. 



As already remarked, these eruptive flocculi probably correspond 

 in many instances with the eruptive prominences observed at the sun's 

 edge. But it must not therefore be concluded that the quiescent 

 calcium flocculi correspond with the quiescent, cloud-like prominences. 

 As a matter of fact, we have good evidence for the belief that the floc- 

 culi shown in these photographs represent in most instances compara- 

 tively low-lying vapors, which, if observed at the sun's edge, would 

 hardly project appreciably above the level of the chromosphere. 



In a few cases, represented, perhaps, by the dark calcium flocculi 

 found on certain photographs, the quiescent calcium prominences have 

 been recorded in projection on the disk. But such instances will re- 

 main exceptional until a spectroheliograph has been constructed of 

 such high dispersion as to permit photographs to be made with the 

 light of the K 3 line exclusively. 



So far we have considered the photography of the sun with the 

 light of the // and A" lines of calcium. But it must naturally occur 

 to any one familiar with the solar spectrum that it should be possible 

 to take photographs corresponding to other lines, and thus represent- 

 ing the vapors of other substances. In the solar spectrum some 20,000 

 lines have been recorded in the great photographic map and catalogue 

 of Bowland, representing almost all the elements known on the 

 earth, and doubtless including many of the radiations of substances 

 which are as yet unknown to terrestrial chemistry. Just as the gas 

 helium was discovered in the sun long before it was round by Bamsay 

 in the laboratory, so we may confidently expect that many other sub- 

 dances represented by lines in the solar spectrum will ultimately be 

 detected on the earth. 



.\<>\v these lines, like the // , and A', hands, are dark, and at first 

 sight it might be supposed that for this reason the vapors corresponding 

 with them could not he photographed with the spectroheliograph. Hut 



