observed at Sea. 441 



brown haze upon the horizon immediately under the centre of 

 the arc, which, although very faint, appeared from its position 

 to have some connexion with the squall or with the rainbow ; and 

 I was thus induced to watch it attentively. At first it was a 

 mere indefinite tinge of colour on the distant horizon, and for 

 two or three minutes it seemed to undergo no change; but at 

 length by slow degrees it increased in intensity, and then ap- 

 peared to spread over the water, looking as though a cloud of 

 reddish dust was hanging over the sea. For some minutes I was 

 quite at a loss how to account for it, but carefully watched to see 

 what would be the upshot. It now became rapidly intensified 

 in brightness, and presently prismatic, and then slowly spread 

 forward across the sea towards us, and at length presented the 

 appearance of a brilliant horizontal bow lying upon the sea, its 

 apex just capping the horizon, and its limbs seeming to fade 

 away upon the water halfway between the eye and the horizon 

 (Plate III. fig. 4). As the horizontal bow increased in intensity 

 the vertical one gradually faded away, and quite vanished imme- 

 diately after the former had reached its greatest brilliancy, which 

 was most marked about the centre or apex. 



In the horizontal bow the red colour was upon the outer or 

 convex side, while in the vertical bow the red was on the inner 

 or concave side. The horizontal bow was therefore the primary 

 bow, and the vertical bow the secondary or reflected one. Hence 

 we had the remarkable spectacle of a secondary bow appearing 

 before the primary bow was at all developed, and fading in pro- 

 portion as the latter reached its greatest intensity. The vertical 

 bow, however, was always much less bright than the horizontal 

 bow ultimately became. This latter, when once the prismatic 

 colours became fully developed, seemed rapidly to approach us 

 from the horizon, the limbs appearing to shoot forward, beco- 

 ming broad, and spreading a wide coloured space upon the blue 

 water on either side ; and the bow, when complete, had some- 

 what of a horseshoe-shape, as though foreshortened. When it had 

 reached its greatest intensity, being then of amazing brilliancy, 

 it suddenly faded and disappeared, and the vertical bow, which 

 had been growing very faint, disappeared at the same time. 

 Throughout the whole duration of the phenomenon the apex 

 of the horizontal bow maintained precisely its original position 

 upon the horizon, namely where I had first been struck by 

 the appearance of the luminous haze; and from the time I 

 first observed this appearance till the time when the whole 

 vanished was about ten minutes. During this time a small 

 drizzling rain fell, which was scarcely sufficient to wet the deck, 

 and the squally effect passed away to the S.W. 



Phil. Mag. S. 4. Vol. 34. No. 232. Dec. 1867. 2 G 



