THE EARTH. 153 



and, immediately after, another noise was heard, like the rattling of 

 a great cart, upon a stony pavement ; which was, probably, nothing 

 more than the echo of the former sound. Its magnitude, when at 

 Bononia, appeared twice as long as the moon, one way, and as broad 

 the other ; so that, considering its height, it could not have been less 

 than a mile long, and half a mile broad. From the height at which 

 this was seen, and there being no volcano on that quarter of the world 

 from whence it came, it is more than probable that this terrible globe 

 was kindled on some part of the contrary side of the globe, in those 

 regions of vapours, which we have been just describing ; and thus, 

 rising above the air, and passing in a course opposite to that of the 

 earth's motion, in this manner it acquired its amazing rapidity. 



To these meteors, common enough southward, we will add one more 

 of a very uncommon kind, which was seen by Ulloa, at Quito, in 

 Peru ; the beauty of which will, in some measure, serve to relieve 

 us, after the description of those hideous ones preceding. " At day- 

 break," says he, " the whole mountain of Pambamarca, where we 

 then resided, was encompassed with very thick clouds ; which the rising 

 of the sun dispersed so far, as to leave only some vapours, too fine to be 

 seen. On the side opposite to the rising sun, and about ten fathoms 

 distant from the place where we were standing, we saw, as in a look- 

 ing-glass, each his own image ; the head being, as it were, the centre 

 of three circular rainbows, one without the other, and just near enough 

 o 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 disposition and 

 order. But, what is most remarkable, though we were six in num- 

 ber, 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 beginning, 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 phe- 

 nomenon, 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, bordered with an orange ; and the last bor- 

 dered by a bright yellow, which altered into a straw-colour, and this 

 turned to a green ; but, in all, the external colour remained red." 

 Such is the description of one of the most beautiful illusions that has 

 ever been seen in nature. This alone seems to have combined al 

 'he splendours of optics in one view. To understand the mannei, 

 therefore, how this phenomenon was produced, would require a per- 

 fect knowledge of optics, which it is not our present province to/ 

 enter upon. It will be sufficient, therefore, only to observe, that all 

 these appearances arise from the density of the cloud, together with 

 Hs uncommon and peculiar situation, with respect to the spectator 

 and the sun. It may be observed, that but one of these three 

 rainbows was real, the rest being only reflections thereof. It 

 ma> also be observed, that whenever the spectator stands between 



