238 Rev. W. Scoresby on some remarTaable Rainbows. 



sea, near the northern coast of Ireland, approaching the entrance 

 of the North Channel. It occurred about half an hour before 

 sunset. There was not a breath of wind at the time ; and the 

 sea was remarliahly smooth and calm. The atmosphere was 

 full of heavy rain clouds, except in the direction where the sun 

 was, and these were discharging showers in various quarters. 



Since this description was originally written (the above ac- 

 count being taken in substance from my journal kept at the 

 time), a very simple explanation has occurred to me of this phe- 

 nomenon, which, at the time of its appearance, seemed to par- 

 take so much of the nature of a prodigy. 



The sea, on this occasion, it has been'remarked, was quite 

 smooth and calm ; its surface, indeed, was like a mirror ; for our 

 situation, being almost " land-locked,'" happened to shut out 

 whatever swell there might be in the main ocean, and likewise 

 to afford time, during a day chiefly calm, for even the smaller 

 waves, of the " wind-lipper,*" to subside. In consequence of 

 these circumstances, the sea, at the close of the day, was with- 

 out the slightest undulation. The sun, at the time when the 

 rainbows appeared, was at a very low altitude. I assumed it 

 in my notes at S*' ; though being above half an hour before 

 sun-set (6 p. m,), it must have been at least twice as great, pro- 

 bably betwixt T and 8°. 



Under such circumstances, there would be a reflection of the 

 sun, from the surface of the water, almost half as strong as the 

 rays proceeding direct from the sun itself * ; which power of 

 rays was fully adequate to the production of a rainbow of near- 

 ly one-half the intensity of the common bow ; and the direc- 

 tion of these rays being from a position, as much below the ho- 

 rizon, as the sun was at the time above it, the arches of the di^ 

 rect and reflected bows, would, of course, be differently situated, 

 as arising from circles of equal diameter, whose centres were 

 twice the altitude of the sun, or 15° apart. The reflected bow 

 (as to the part above the horizon) would consequently be a seg- 

 ment larger than a semicircle, and precisely as much larger as 



* The quantity of rays reflected by water, according to Sir Isaac Newton, when 

 incident at an angle 74° inclined to the horizon, is about four-tenths of the whole 

 quantity that reaches the surface. 



