Oh. XXn.] HORIZONTAL EAINBOW. 385 



I have alluded in some parts of this volume to remarkable 

 atmospheric effects occasionally met with in the open ocean ; 

 but none were more singular than the horizontal rainbow 

 which I witnessed on May 5th, in lat. 25° 19' S., and longi- 

 tude 54° 13' E. The weather was very fine and bright, and 

 we were sailing gently along with a light breeze, when I ob- 

 served signs of a squall blowing up from the S.S.E. I was 

 sitting reading on deck at the time, and immediately went 

 over to the port gangway to watch its approach. It was 

 about half-past one p.m., and the sun was therefore in the 

 N.N.W., exactly opposite the approaching squall, upon which 

 was already developed a rainbow of low altitude (12° to 15°). 

 While gazing at it my attention was arrested by a yellowish- 

 brown haze upon the horizon immediately under the centre 

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

 position to have some connection with the squall or with the 

 rainbow ; and 1 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 appeared to spread over the water, look- 

 ing 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 up- 

 shot. It now rapidly intensified in brightness, and presently 

 became prismatic ; then slowly spreading forward across 

 the sea towards us, it 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. As 

 the horizontal bow increased in intensity the vertical one 

 gradually faded away, and quite vanished immediately after 



