ii HALO 13 



Let me explain how it is formed. When a stone 2 

 is thrown into a pond, the water is observed to 

 part in numerous circles, which, very narrow at 

 first, gradually widen out more and more until 

 the impulse disappears, lost in the surface of the 

 smooth water beyond. Let us suppose something 

 of the same kind to occur in the atmosphere. 

 When condensed it is capable of receiving an im- 

 pact : the light of sun, moon, or any heavenly body 

 encountering it forces it to recede in the form of 

 circles. Moisture, be it observed, and air, and 

 everything else that takes shape from a blow, is 

 driven into the same form as that possessed by the 

 object that strikes it. Now every kind of light is 3 

 round. Therefore, the air when struck by light will 

 assume this form. Accordingly the Greeks gave 

 the name Threshing-floor (i.e. Halo) to a brightness 

 of this kind, because spaces set apart for threshing 

 corn were, as a rule, round. 



Be the better name threshing-floors, or be it 

 crowns, there is no reason to suppose that they 

 are formed in the neighbourhood of the heavenly 

 bodies. They are a very long distance from 

 them, though as seen from the earth they seem 

 to touch and encircle them. In reality such an 4 

 image is formed not very far from the earth, but 

 the wonted frailty of .human vision is deceptive, 

 and we imagine the ring is formed close round the 

 heavenly body itself. But no such thing could 

 possibly occur in the neighbourhood of the sun and 

 stars, as there is nothing but thin ether there. It 

 is only when bodies have become rough and dense 

 that shape can be impressed upon them. In subtle 

 bodies there is no point on which form can lay hold 

 or to which it can adhere. A phenomenon of the 



