ScHAW.— O^i Tico Triple Boivs seen at Invercargill. 517 



refract the light at a definite angle of ahout 46°, and thus a 

 second coloured ring outside the first is perceived ; and in 

 both, the refraction being produced directly without internal 

 reflection, the colours are arranged in the same sequence, 

 red inside and blue outside. 



The third circle of white light sometimes observed outside 

 the other two coloured rings is probably produced by reflec- 

 tions from the surfaces of the ice-crystals without refraction 

 by the light passing through them. 



Iia the bows seen at Invercargill the axes of the cones of 

 coloured or white light producing the appearances were at 

 right-angles to the parallel rays of moonlight — not coincident 

 with them, as in ordinary halos. The phenomenon was there- 

 fore, I conceive, caused by reflection previous to refraction — 

 reflection from the inclined surfaces of myriads of ice-crystals, 

 which happened to be in the right position to reflect the inci- 

 dent rays outwards from the walls of frozen mist ; their 

 reflected rays passing through other crystals, and being re- 

 fracted in their transit through them, gave rise to the 

 divergent coloured rays, which produced in the eye of the 

 spectator the arches seen both to the north and to the south. 

 I think that in this way the effect was produced ; for, although 

 by an interior reflection in a prism coloured rays would be 

 projected backward towards the source of light, I have not 

 been able to find any position of the prisms that would 

 account for the symmetrical arches on the theory of internal 

 reflection. 



The reflection from the outer surfaces of other crystals 

 would doubtless weaken the light ; but, as compared with 

 ordinary halos, in which the light which reaches the eye has 

 passed completely through a cloud, and has undergone very 

 numerous reflections and refractions in its transit, the Inver- 

 cargill appearance would have the advantage that the light 

 would have been reflected and refracted at the outer surface 

 of the cloud, and so would have lost less by absorption and 

 dispersion than in the more ordinary appearance of the circular 

 halo round the sun or moon ; and this would be the more ti'ue 

 if, as I suppose, the clear avenue in which the spectator stood 

 was V-shaped — wider at the western end towards the moon 

 and narrowing towards the east. 



The straight ray of white light tangential to the northern 

 white bow at its west end, which appeared only for a short 

 time, may have been due to a local current of air which turned 

 the majority of the ice-crystals there in a direction which 

 reflected the moonlight ; but it is very much more probable 

 that it was the result of some of those intricate effects of 

 refraction and reflection which produce the reversed circles 

 sometimes seen in connection with halos, and those phenomena- 



