16 Teneriffe. | Jan., 
been thought unnatural. From the clearness of the atmosphere, 
the light given by the stars and planets was sufficient to enable me 
to write my observations, and Venus left a faint glimmering streak 
of light on a wreath of snow close to our resting-place ; and when 
the moon arose, I could distinctly see the degrees on my instru- 
ments. A still stronger proof of the extreme clearness of the 
atmosphere was, that I observed the moon to be indented like a 
saw, between the light and obscured part, which I supposed was 
caused by the projection of the illuminated tops of the mountains 
upon the part which was deprived of the sun’s light. 
Soon after dark a broad pyramidal body of light appeared, like 
the glow on the sky caused by a distant conflagration ; this was the 
zodiacal light; where there were openings in the clouds below, the 
brightness continued close down to the horizon, with as deep a 
tone as that of the zenith. It was much broader below, oc- 
cupying a space equal to what I considered to be nearly 15° in 
breadth. Orion was so clear, that if I had had a telescope of 
even moderate power, no doubt I might have seen the whole of his 
sword. 
Another phenomenon I observed may be worth mentioning. 
Soon after the sun went down, the wind became much louder and 
had an acuter sound, although the force was very considerably less 
than it was before. It has been observed, from the earliest anti- 
quity, that the air becomes more sonorous at night than in the day, 
but Iam not aware that the cause of it has been well ascertained. 
The general opinion is, I believe, that the air, becoming colder, is 
therefore denser, and more susceptible of conveying the sonorous 
waves. Our navigators to the North Pole have frequently mentioned 
the surprising distance from which they were enabled to hear sound 
during an Arctic winter. My observations of the intensity of 
sound at different states of the atmosphere were not confined to 
the Peak. At the town of Orotava, situated about two miles from 
the sea, the noise of the waves in the morning occasionally had a 
grave, low tone ; at the same time, the air appeared to be particularly 
dry, and distant objects were very indistinct. Towards the middle of 
the day, or the beginning of the afternoon, and when the difference 
between the dry and wet bulb thermometer was /ess than usual, 
the island of Palma, nearly sixty miles distant, could be distinctly 
seen, and the mountains that surround the valley of Orotaya 
were brought apparently so close, that the vegetation upon them 
could be observed ; at the same time, the sound of the sea invariably 
passed from a grave to an acute sound. The natives prognosticate 
rain when they observe this particular clearness of the atmosphere, 
and generally I have found them correct. I have made the same 
remark during my long residence in Chili, where the distant Andes 
are apparently only a few miles off shortly before rain, and the 
