228 Ascent to the Summit of the Popocatepetl. 
sand feet in the air, remarkably excited our imaginations. We 
should have liked to have gone all round, but we had not time, and 
I believe we had not sufficient strength. 
At three o’clock the thermometer was at —1—4 centigrade. The 
moist belt of the hygroscope appeared at 34°, and disappeared at 
33° of the interior Fahrenheit thermometer, whilst the exterior ther- 
mometer was at 40°. 
In consequence of the violence of the wind, we were unable to 
light the spirit-of-wine lamp for boiling water; but that which was 
much more unfortunate was, that in turning over the barometer for 
the purpose of running the quicksilver into the ball, some globules 
of air got into the tube : the instrument became comparatively useless. 
If you read attentively the description I have given you of the 
volcano, you will, no doubt, be struck with two things. The first 
is the singular disposition of the apertures through which the va- 
pors exhale. They are at the bottom, and in a circle; so that 
those yellowish walls, a thousand feet high, and a league in circum- 
ference, appear as a screen to chimney flues conducting the vapor 
to the highest level of the ground. ‘The second is the extraordinary 
coating of the interior of the crater. All those layers of lava, of 
sand, of stone, which form the mass of the volcano, are of the same 
nature on the outside as on the inside of the crater ;—on the outside, 
however, all is black, purple, and red; whilst on the inside a dirty. 
white and yellowish hue prevails. There is therefore either a de- 
composition of the volcanic substances by the sulphurous gas, or a 
deposit of sulphur on the edges—perhaps both. We unfortunately 
could not get any of these whitish substances; and M. de Gerolt, 
who tried, was near paying dearly for his imprudence. He had de- 
scended by an inclined plane into one of the rents of the crater ; but 
the sand was giving way under his feet, and he was sliding down to- 
“wards the abyss, when he was fortunate enough to save himself with 
‘his iron-shod stick. It would, no doubt, have been magnificent to 
have had such a grave ; but my travelling companion’s ambition did 
not seem to extend so far. 
If we were well agreed on this point, there was one on which we 
were not equally so, This was a strong and prolonged noise, which 
we heard at times from the interior of the volcano. We felt no 
motion, and nothing was thrown up from below. M. de Gerolt ad- 
mitted that this noise was such as might be made by detached stones 
from the upper part of the crater falling down on the inclined plane 
