1866. | Teneriffe. 17 
noise of the waves of the sea, dashing on the rocky coast, assumes 
a different tone. 
From frequent observations that I have made, I am inclined to 
attribute the intensity of sound at night to a certain increase of 
‘moisture, and to an eqguabdlity of temperature in the different strata 
of the atmosphere. The increased intensity of sound when I was 
on the Peak during the night could not have been caused by an 
increased density of the atmosphere, because, instead of becoming 
colder, it was four or five degrees warmer when the sound of the 
wind became more sonorous. 
The instruments were observed every hour, and the boiling- 
point of water was noted four times, giving an average of 193°: 64; 
the barometer, an average pressure of 2)°°329. This boiling-pomt 
does not exactly agree with the experiments of General Roy, who 
_considered that the boiling-point of water varied 0°88 of a degree 
for every half-inch of a variation of the barometer At the Villa 
de Orotava, at an elevation of 1,141 feet, I found the average 
boiling-point to be 209°-178,— the thermometer was not in the 
water, but close above it. In the subjoined table I merely give 
the result of my observations at such times as there were notable 
differences. The difference of radiation was most astonishing: as 
night approached it fell 80° im an hour; at midnight it was nega- 
tive, that is, the shaded thermometer was 9° higher than the 
exposed one. At first I thought it must be caused by local 
position, but I removed the thermometers three times, and found 
the results similar. I was surprised to find that, at the moment of 
sunrise, it was still negative, the shaded thermometer standing 4° 
higher than the other. At Alta Vista de Arriba, one hour and a 
half after sunrise, the black-bulb thermometer rose to 98°, and 
later to 126°. 
The following table is the result of my observations made at La 
Estancia de los Ingleses, 9,930 feet above the level of the sea:— 
Shelter ack- -poi iling-poi 
Hour. ce aecien meee ce esac en Maen | Sve 
CO? PM: 50 195 46 193°65 20-334 
3.30 ,, 49 190 45 193°62 | 20-330 
UO es 36 39 40 193°61 20°527 
Midnight. 38°5 29°5 31 —_ 20-324 
2.0 A.M. 38°5 27 5 30 — | 20°3823 
Dine 36°5 32°5 35 = | 20-331 
| Noon. ! 66 212 60 193°68 | 20°336 
About an hour before sunrise I awoke my sleepy men, but my 
guide (who had never ascended to the top of the Peak) was 
seized with an affection like sea-sickness, and a violent pain in the 
head, no doubt caused by the rarity of the air, therefore I was 
obliged to leave him at the Estancia to await my return. 
VOL. III. é 
