HISTORY OF 



own image ; the head being, as it were, the 

 centre of three circular rainbows, one without 

 the other, and just near enough to each other as 

 that the colours of the internal verged upon those 

 more external; while round all was a circle of 

 white, but with a greater space between. In this 

 manner these circles were erected, like a mirror, 

 before us ; and as we moved they moved, in dis- 

 position and order. But, what is most remark- 

 able, though we were six in number, every one 

 saw the phenomenon, with regard to himself, and 

 not that relating to others. The diameter of the 

 arches gradually altered, as the sun rose above 

 the horizon ; and the whole, after continuing a 

 long time, insensibly faded away. In the begin- 

 ning, the diameter of the inward iris, taken from 

 its last colour, was about five degrees and a half; 

 and that of the white arch, which surrounded the 

 rest, was not less than sixty-seven degrees. At 

 the beginning of the phenomenon, the arches 

 seemed of an oval or elliptical figure, like the 

 disk of the sun, and afterwards became perfectly 

 circular. Each of these was of a red colour, bor- 

 dered with an orange, and the last bordered by a 

 bright yellow, which altered into a straw colour, 

 and this turned to a green ; but, in all, the ex- 

 ternal colour remained red." Such is the des- 

 cription of one of the most beautiful illusions that 

 has been ever seen in nature. This alone seems 

 to have combined all the splendours of optics in 

 one view. To understand the manner, therefore, 

 how this phenomenon was produced, would re- 

 quire a perfect knowledge of optics ; which it is 



