256 Bigelow — Magnetic Theory of the Solar Corona. 



accordance with Ebert's experiment. (3) The equatorial regions 

 of the sun usually show that there is a tendency to form a 

 trumpet-shaped extension along the ecliptic, widening in pro- 

 portion to the distance from the sun. This is another evidence 

 of the fact of mutual electrical repulsion between the charged 

 ions of like sign, since the spreading is similar to that of the 

 cathode bundle in a vacuum tube. Hence we see that there is 

 a tendency for the rays to diverge from the poles towards the 

 equator, and for the equatorial rays to spread in opposite direc- 

 tions towards the poles, the former under magnetic and the 

 latter under electrostatic forces of repulsion. The combined 

 effect is to accumulate the ions in a quadrantal or synclinal 

 structure near latitudes of 45 degrees, as is observed to be the 

 case. The 11-year periodic change in the coronal structure is 

 probably due to a variation of the balance between these two 

 systems of forces, that of the magnetic polar structure domi- 

 nating in minimum years, that of the electrostatic development 

 in maximum years, and the quadrantal or compromise forma- 

 tion in the middle portions of the period. The polar rifts and 

 the visible rays are to be referred to the same principles* as 

 control the formation of striae in the luminous vacuum tubes, 

 that is to the variation of density in the number of the ions 

 per unit volume. The rays are the places of recombinations 

 of the ions under excessive density of their number, and the 

 dark spaces are the loci of the ionization or dissociation, the 

 former occurring at the places of maximum and the latter at 

 places of minimum of the external impressed electric forces 

 which produce the coronoidal discharge. The details of sev- 

 eral experimental theories which are thus united for an expla- 

 nation of the sun's corona, together with the promise of 

 further developments along the same lines is very encouraging. 

 The coronal pictures on a large scale taken in May, 1900, are 

 entirely in accord with this theory ; also Professor Wood'sf 

 comment on Abbott's measurement of the coronal heat, that 

 the absence of heat rays is due to the smallness of the particles 

 of matter in the corona, which emit little incandescent light, 

 but reflect relatively more polarized light, may be understood 

 to indicate that there exists in the sun a true form of cathode 

 radiation, rather than the Kontgen or any other subform of 

 radiation. The objection that the sun's high temperature is 

 fatal to the hypothesis that it possesses a strong magnetic field 

 is met in two ways. (1) The earth is very hot and yet carries 

 a magnetic field depending upon the material of the interior ; 

 and (2) the great pressure in large bodies probably maintains 



* J. J, Thomson, Phil. Mag., March, 1899. J. H. Jeans, Phil. Mag., March,. 

 1900. 

 f Science, February 1, 1901; Astrophysics, January, 1891. 



