﻿in Total Eclipses of the Sun, 229 



extending indefinitely outward from the sun into space, and 

 elongated in the plane of his equator, and that to observers 

 on the earth it would have an apparent form more or less 

 triangular. 



The same fundamental conception which accounts for the 

 solar corona and the physical relations known to subsist be- 

 tween the sun's spots and terrestrial auroras, as well as between 

 these spots and the varied magnetic disturbances occurring on 

 the earth, furnishes, then, an adequate explanation of the extent, 

 form, and position of the Zodiacal Light. In fact we see that 

 the zodiacal light is but the indefinite extension of the corona. 



We have here tacitly supposed that the solar emanations 

 consist of magnetic matter projected with great velocity into 

 space in the directions of the prolongations of the auroral 

 columns, and proceeding on indefinitely in these directions; 

 but if, like the cometic matter, they are exposed to a continual 

 repulsion from the sun, the paths described by the receding 

 particles would be hyperbolas convex towards the sun. The 

 point of intersection of any two streamers proceeding from 

 corresponding low latitudes in the two hemispheres, would 

 in consequence be thrown to a greater distance from the sun ; 

 but the general result, as to the form and position of the 

 luminous appearance produced (the zodiacal light), would be 

 the same. 



In support of this view of the origin of the zodiacal light, we 

 may state that Cassini drew from his observations on the sun's 

 spots and the zodiacal light, made during the interval from 

 1665 to 1688, the conclusion that a physical connexion sub- 

 sisted between these two phenomena, and that the substance of 

 the zodiacal light was, in fact, some emanation from the sun's 

 spots. Again, according to Arago, it appears, from the entire 

 series of observations at Paris and Geneva, that the zodiacal 

 light varies considerably from one year to another, and that the 

 observed variations cannot result entirely from changes in the 

 transparency of the atmosphere. We shall soon see that the 

 form of the corona, as seen in the eclipse of 1869 and previous 

 eclipses, presented certain prominent features that accord with 

 the theoretical conclusion that the zodiacal light is but the 

 indefinite extension of the corona. 



It is proper to state here that in what precedes we have really 

 been contemplating but different sides of one comprehensive 

 theory, which embraces a connected series of solar phenomena, 

 of which the corona is but one term. The outline of this 

 theory is given in the author's ' Treatise on Astronomy,' revised 

 edition (1867). It is : — that a portion of the matter of the sun's 

 photosphere is in the habitual condition of auroral magnetic 



