Summit of the Peak of Tcneriffe in February 1829. 249 



decrement is in arithmetical progression : but these opinions 

 I think will be found to be incorrect. 



From various observations made during expeditions to the 

 Peak, it appears, that the decrease of temperature is more 

 rapid in the inferior strata of the atmosphere, and slower in 

 the superior, but at a certain high elevation (which possibly 

 varies according to the latitude) the thermometer in the sum- 

 mer season is almost stationary throughout the twenty-four 

 hours ; and that even in winter, during the middle of the day 

 at the same elevation, the temperature is nearly similar to 

 what it is in summer, and in Teneriffe the height of this 

 stratum of air is from nine to eleven thousand feet. 



If the decrease be uniform, the mean heat of a certain eleva- 

 tion will be found by a thermometer placed between the lower 

 and upper stations : but this is not the case ; and from the 

 tables which I have subjoined, it will be seen that the error is 

 much greater when the decrease is taken in arithmetical, than 

 in geometrical progression. In this country, the temperature 

 of the atmosphere is said to diminish, in proportion to the 

 height above the level of the sea, at the rate of one degree of 

 Fahrenheit for every 270 feet of ascent. If the temperature 

 fell in the same ratio at Teneriffe, there ought to be a difference 

 of about 45° between the temperature of the coast and the top 

 of the Peak, whereas the maximum difference which I ex- 

 perienced was only 18^°. It is true, that it is impossible to 

 know the exact temperature of any point by a single passing 

 observation, as the thermometer must vary every moment ac- 

 cording to the presence of the sun, the interposition of clouds, 

 a strong wind, or a calm : a local fog may occasion a refrigera- 

 tion 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 obser- 

 vation. These can all be 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 be ascribed to the incorrectness of the theory ; and 

 although it may never be submitted to accurate calculation, 

 from the variety of disturbing causes, yet it may be brought to a 

 near approach to truth. 



It is much to be desired that some learned Society would 

 pay attention to this problem, and resolve it by direct expe- 

 riment, by establishing on the Peak a set of observations. It 

 would be easy to find men courageous enough to undertake it : 

 although it is covered with snow every year for the space of six 



N. S. Vol. 8. No. 46. Oct. 1830. 2 K or 



