ATMOSPHERE OF THE SUN DESLANDRES. 353 



the solar vapors by placing side by side small spectra of successive 

 equidistant sections of the solar disk by means of a second large slit 

 and discontinuous, automatic movements. It is a complement to the 

 spectro-heliograph and fully as useful. It tells us besides the radial 

 velocities, the general form of the vapors, and the details of the whole 

 line, particularly the width of the isolated line which is very variable 

 from one part of our star to another. It gives us information at 

 points where the spectro-heliograph fails, for the latter can not with 

 a slit of constant width isolate accurately a line of variable width; 

 in short, it records all the elements which escape the spectro-helio- 

 graph and assures an accurate interpretation of the results. 



A naked-eye examination of the plates taken with the K line shows 

 at once that the radial movements are in general more noticeable 

 on the filaments than at the adjacent points. Sometimes even all the 

 K 3 lines due to the filament are inclined in the same direction and 

 show a whirl about a horizontal axis as distinguished from that which 

 exists in the sun spots about a vertical axis. But to this movement 

 there succeeds, as with the spots, a relative calm. If then we were to 

 measure with care these displacements and the radial velocities in 

 the K 3 line when the vapor is at the center of the disk we would find 

 that the vapor is rising with a velocity often greater than the ve- 

 locity of rotation of the sun at the equator (some 2 kilometers per 

 second). This has been verified for several filaments. Aside from 

 the spots and the filaments, the vertical velocities in the upper strata 

 are not insignificant and often of the same order as the equatorial 

 speed of rotation. The magnitude of this vertical motion is less 

 astonishing when we note that the gaseous mass of which the atmos- 

 phere is composed lies above an intense furnace of heat. 



Analogous measures have been made carefully at the center of the 

 sun on faculse and flocculi with the reverse result. The vapor 

 here has a contrary direction of motion and descends while in the 

 relatively dark portions around there are ascending currents. Gen- 

 erally at the bright places of the K 3 images of the upper layer the 

 vapor descends ; it ascends where the image is relatively dark. That 

 is really logical, for the vapor which goes down becomes compressed 

 and therefore becomes warmer, while that which rises expands and 

 becomes cooler. 



This phenomenon, which has already been noted on a great num- 

 ber of plates, is important, for it shows the special structure of the 

 atmospheric strata, indicating that they are divided into convection 

 currents exactly as in the case with liquids heated uniformly at 

 their lower surfaces in our laboratories. 



The bright faculse often cover a remarkable extent of the image 

 and often with sharply formed juxtaposed polygons exactly similar 



97578°— sm 1910 23 



