72 REPORTS ON INVKSTIGATIONS AND PROJECTS. 



interpretation of the principal phenomena of strengthened and weakened 

 lines, at the same time permitting an estimate of the approximate temper- 

 ature of the vapors within the spot. Our work also appears to throw 

 light on the much discussed question of the "enhanced" lines, favoring, as 

 it does, the view that temperature alone is sufficient, in most cases, to 

 account for these lines, though by no means precluding the view that high 

 electrical potential, or sudden change of potential, may be capable of pro- 

 ducing similar effects. Special attention will be given to these latter 

 questions in our laboratory investigations. 



Radial Motion of the Calcium Vapor in the Floccuei. 



In connection with the study of the spectra of sun-spots, the work of 

 Mr. Adams on the wave-length of the H and K lines in the flocculi, and 

 the motion of the calcium vapor in the sun,* is of great importance. As 

 the spectroheliograph so clearly shows, sun-spots are surrounded by ex- 

 tensive flocculi, consisting of cloudlike masses of calcium vapor, which 

 sometimes overhang the smaller spots, so as to hide them completely. 

 These calcium clouds rise from the faculse, and they are presumably the 

 effects of convection currents proceeding outward from the interior 

 of the sun. It is evident that the radial motion of the vapor should 

 be measurable from the displacements of the H, and K, lines, which 

 correspond to the lower and intermediate regions of the chromosphere, 

 and those of the H3 and K3 lines, which are produced by the absorption 

 of the cooler vapor at a somewhat higher level. Mr. Adams's investiga- 

 tion began with a redetermination of the wave-lengths of the H and K 

 lines in the electric arc, since the available determinations were not in 

 sufficiently close agreement to promise the necessary accuracy. The 

 large scale of the photographs, which were made with the Littrow spec- 

 trograph, permitted them to be measured with high precision, and the 

 resulting wave-lengths of the H and K Hues are probably very close to 

 the truth. Using the arc lines as standards, Mr. Adams determined the 

 wave-lengths of the Hj and K2 lines, and those of the H3 and K3 Hues, 

 at various points on the solar surface, and also (for the latter lines) over 

 sun-spots. The average displacement of H3 and K3, which amounted to 

 0.006 tenth-meter toward the violet, corresponds to a velocity of approach 

 of the calcium vapor amounting to 0.41 kilometer per second. The vary- 

 ing displacements obtained at different times, however, indicate that gen- 

 eral conclusions should be based only on a very extensive investigation. 

 The results given by the bright lines H, and K. also show a displacement 

 toward the violet, so that it is probable that the calcium vapor in the 

 flocculi may be regarded as moving upward. This would accord with 

 the conclusions as to the nature of these objects based upon work with 



* Contributions from the Solar Observatory, No. 6. 



