1866. | Teneriffe. 23 
actual experience and of numerous observations I made during my 
residence at Teneriffe. 
From yarious observations I made at different elevations in 
Teneriffe, it is evident that the decrease of temperature is more 
rapid in the inferior strata of the atmosphere, and slower in the 
superior, but at a certain elevation (which possibly varies according 
to the latitude) the temperature in the summer season is almost 
stationary throughout the twenty-four hours; even in winter, 
during the middle of the day at the same elevation, and in Teneriffe 
the height of this stratum of air is from nine to eleven thousand 
feet. 
If the decrease be uniform, the mean temperature of a certain 
elevation will be found by a thermometer placed between the lower 
and upper stations ; but this is not the case, the error being much 
larger when taken in arithmetical, than in geometrical progression. 
The temperature at Port Orotava was. . F Gios5 
That on the top of the Peak at the same time : 45°° S75 
Difference between the two stations . : 15> G25 
“If the temperature had decreased in arithmetical pro- 
gression, that on the top ought to have been . —15°:94 
Or a difference between the two of : ; : 77°44 
Instead of which I found it to be only . : 15° 625 
The following figures will show the difference of temperature 
per 1,000 feet: the difference of temperature between Port and 
Villa Orotava gave 5°°726 as the average difference per 1,000 
feet of elevation; while between the Port and the Estancia de los 
Ingleses the average difference of temperature per 1,000 feet was 
only 2°:43. Taking the difference of temperature between the 
Villa Orotava and the Estancia de los Ingleses, it would be 
necessary to ascend 537°75 feet for an alteration of one degree of 
temperature, but between the Villa and the summit of the Peak, 
it would be necessary to ascend 1,317 feet for one degree of 
difference in temperature. 
Tt is, however, impossible to know the exact temperature of 
any point by a single passing observation, as the thermometer may 
vary every moment according to the presence of the sun, the inter- 
position of the clouds, a strong wind, or a calm; a level fog may 
occasion a refrigeration in that part of the atmosphere where the 
instrument is situated, which the rest of the air may not partake 
of; and any of these accidents may occur at the precise moment of 
observation. These can be all allowed for to a certain degree of 
correctness, but the immense difference between the supposed and 
observed decrement of heat, from the sea-coast to the top of the 
Peak, cannot be attributed to the effect of local causes, but must 
