Eclipses 



extremely feeble under ordinary conditions; 

 it has, however, been observed and measured 

 by means of very delicate experiments, which 

 fully confirmed the opinions expressed by 

 Maxwell. It is therefore natural to admit 

 that the intense radiation of the photosphere 

 repels the cosmic dust forming the solar halo 

 and the tail of comets, and this view presents 

 the advantage of affording a simple explanation 

 of some of the appearances observed. It has 

 been established, first of all, that in contrast 

 to what happens with the gaseous corona the 

 development of the halo is greater during periods 

 of solar quiescence. Now these periods of 

 quiescence, during which sun spots are few and 

 small, appear also to coincide with maxima of 

 radiation from the photosphere, and consequently 

 with maxima of the repulsive action of this radia- 

 tion on the coronal dust. Moreover, the plumes 

 of the halo are not directed along radii of the 

 sun; they seem to shoot off from the polar 

 axis around which the entire solar mass turns, 

 and to bend towards the equatorial zone, where 

 they spread in long streamers. This disposition 



appears to be due to the centrifugal force, 



217 



