458 THE POPULAR SCIENCE MONTHLY 



extends the solar corona which reaches enormous distances into space. 

 The corona is apparently composed of minute dust particles and ionized 

 atoms and molecules held in certain positions by the action of electric 

 and magnetic forces. The photosphere is penetrated in certain re- 

 gions by solar spots which extend from the upper levels of the photo- 

 sphere into the interior. It has been shown by recent photographs 

 taken at the Mount Wilson Observatory that the sun spots are closely 

 associated with motions so like those pertaining to the sections in a 

 dumbbell-shaped vortex that the analogy appears to be very complete. 

 If this is so, then terrestrial meteorology becomes intimately connected 

 with solar meteorology in many of its features, in spite of the great 

 differences of temperature. The average temperature of the earth's 

 atmosphere may be taken as about 15° Centigrade below zero. The 

 surface of the photosphere is apparently between 7,000° and 8,000° 

 Centigrade, and the sun's temperature increases to more than 10,000° 

 near the nucleus, though the gradient is not yet known. Taking the 

 sun spot region as a whole, the sun spot belts form near latitude 30° 

 north and south of the equator and they gradually drift towards the 

 equator in the course of about eleven years, when new spot belts begin 

 to form. The same is true of the faculse which are closely associated 

 with sun spots. The circulation within the sun spot belt is from the 

 surface downwards, while the spots drift as a whole towards the equa- 

 tor. This indicates, therefore, descent into the sun from the surface 

 in the neighborhood of the equatorial regions, and, of course, to com- 

 pensate this, material must be projected from the interior outwards in 

 the higher latitudes. 



The prominences are hydrogen flames going through a periodic 

 drift. They may be said to appear first in largest numbers in middle 

 latitudes, and they seem to divide into two branches so far as the 

 number of them is concerned. One branch drifts southward in the 

 eleven-year period along with the spots and the faculse. The other 

 branch drifts poleward to the north and to the south, respectively. A 

 study of the number of these prominences in different latitudes indi- 

 cates that there is a periodic change in the apparent velocity of the 

 rotation in the polar regions, fluctuating back and forth in about a 

 mean value. Since the prominences have different elevations, and 

 different levels in the sun have different velocities, it may well be that 

 in the polar regions the prominences develop sometimes in the higher 

 levels and sometimes in the lower levels, so that they actually drift 

 eastward at different angular velocities according to their elevation. 

 The spectroscope apparently indicates a certain angular velocity per- 

 taining to special spectrum lines, which look like a fixed value for a 

 given elevation, and at the same time it has been shown that hydrogen 



