188 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 30 



In sounding the sun's atmosphere from the outside, one would, on 

 passing through the corona, encounter an atmosphere of ionized 

 calcium; to this would be added at successively lower levels, hydro- 

 gen, ionized titanium, sodium, normal calcium, and then other ele- 

 ments in rapid succession until at the photospheric level all constitu- 

 ents would be present. Helium, probably because of its high exci- 

 tation potential, does not appear as an absorption line in the solar 

 spectrum, except over the more actively disturbed areas. It is promi- 

 nent in eclipse spectra and extends to a height of 8,000 km. 



In the second column, the cyclonic whirls in the upper chro- 

 mosphere are indicated by circles. These secondary high-level 

 vortices are probably called into existence through the low tem- 

 perature of the underlying spot umbra, either as a result of the 

 cooling of the lower chromosphere causing a down rush, or more 

 directly as the result of a decrease in the radiation pressure by 

 which the chromosphere is supported. As a rule, the direction of 

 these high-level whirls corresponds in all sun-spot cycles to the 

 terrestrial law, counter-clockwise in the Northern Hemisphere and 

 clockwise in the Southern Hemisphere. For the underlying vortices 

 constituting the sun spots, the whirls are below the photosphere and 

 their directions are unknown. Since the magnetic polarity is 

 opposite in Northern and Southern Hemispheres, and reverses at 

 each spot minimum, we may infer that change of polarity corre- 

 sponds to change in the direction of the whirl in the field-forming 

 vortex (Hale). The directions of the whirls in the upper and lower 

 vortices are independent of each other. In the same column the 

 length of the arrows is proportional to velocity of How, and their 

 directions correspond to the inward and outward motions at high 

 and low levels, respectively. 



In the third column (disk) displacements of high-level lines to 

 the red and of low-level lines to the violet relative to lines of medium 

 level, are similar to displacements that occur in stellar spectra and 

 appear to be a general characteristic of stellar atmospheres, their 

 magnitude increasing with the temperature of the star. The dis- 

 placements for the sun are consistent with its position in the evolu- 

 tionary sequence. As to the displacements of high-level lines to the 

 red expressed in their equivalent (Doppler velocity in the third 

 column of Figure 2), the following considerations offer a probable 

 interpretation. The increase in width of H and K above 8,000 km 

 indicates high ionic agitation. After emission, it is probable that 

 some of these atoms will possess large outward velocities, and hence 

 the next absorption will be from the violet side of the absorption 

 line, where the radiation is much stronger than at the center. Con- 

 secutive emissions and absorptions will therefore endow these atoms 

 with an increasing outward acceleration, and it is possible that some 



