contact with the ſurfaces of bodies, affords a very ſatisfactory explanation of this ſplendid phenomenon. It exemplifies, upon a large ſcale, a fact well known to natural philoſophers; namely, that when the rays of the ſun are made to paſs through a ſmall hole in the window-ſhutter of a darkened chamber, ſo as to fall upon any object within it, they repreſent the outlines of the object in all the various colours of the rainbow, by being collected with a priſm and thrown upon a white ſheet of paper.
We now had to croſs a prodigious heap of pumice-ſtones, amongſt which we obſerved very few vegetables, and thoſe in a very languiſhing condition. The ſpartium was the only ſhrub that could ſupport itſelf in theſe elevated regions. It was very troubleſome walking upon this volcanic ſoil, as we ſunk into it up to the middle of the leg. We found ſome blocks of pozzolana ſparingly ſcattered among the pumice-earth.
At nine o'clock in the evening we took up our abode for the night in the midſt of the lava. Some large fragments that we found, were our only ſhelter againſt the eaſt wind, which blew with conſiderable violence. The cold was very intenſe at this height, where nature has not conſulted the convenience of travellers, as very little wood is found here; ſo that the ſcanty fuel that
we
