356 SMITHSONIAN misc];i,i.ane;ous collections vol. 52 



at higher levels, and thus escaping the effects of friction experienced 

 by the calcium vapor, move at greater velocities in the higher lati- 

 tudes, and show little increase in the equatorial zones. 



It will be observed that the spectrographic velocities, both in the 

 low-lying vapors of the reversing layer and even more markedly in 

 the case of hydrogen, are decidedly greater than the results ob- 

 tained by measuring the daily motions of spots, faculae or flocculi. 

 Is it possible that the flocculi, rising from lower levels, retain, in 

 part, the lower velocities characteristic of these levels? It will be 

 a matter of great interest to study this question, as more measures 

 beconie available. 



Red and Violet Hydrogen Flocculi 



Adams's spectrographic measures of hydrogen make it probable 

 (though hardly certain, as yet) that the rotational displacements of 

 the red hydrogen line {Ha) are greater, on the average, than those 

 of the blue and violet lines (///3 and Hy ; Hh was too diffuse for 

 accurate measurement). The Ha line is also greatly strengthened 

 and widened near the Sun's limb, while the other lines retain about 

 the same intensity they exhibit at the center of the disk. Hence it 

 might be suspected that photographs of the hydrogen flocculi, made 

 with Ha, would exhibit corresponding peculiarities. 



Fortunately the new "Pan-iso" plates, for which we are indebted 

 to Wallace, are remarkably sensitive to red light. They enabled 

 us to try the experiment of photographing the Sun with the Ha 

 line, using the high dispersion of a spectroheliograph of 30 feet focal 

 length, employed with the new tower telescope. The first plate 

 showed large bright hydrogen flocculi, in a region (near a group of 

 small Sun-spots) where an //8 photograph, taken simultaneously 

 with the 5-foot spectroheliograph and Snow telescope, showed only 

 dark flocculi. This first plate, however, was under-exposed, and 

 full timing also revealed dark Ha flocculi. Later it was found pos- 

 sible to make excellent Ha photographs of the entire Sun with the 

 5-foot spectroheliograph. Curiously enough, both the bright and 

 dark flocculi shown by these plates differ in many particulars from 

 the Hh flocculi, though there is a general resemblance of various de- 

 tails (Plate XXXVI ). 



These results have been obtained very recently and no complete 

 explanation of the differences between the Ha and the //8 flocculi 

 has yet been worked out. We found at the Yerkes Observatory that 

 the Hp, Hy and //8 flocculi closely resemble one another, and this 



