IV. CLIMATE. 159 



13. Relation of Mean Temperature to Altitude. — So 

 few and unsatisfactory are the data on which to ground a 

 scale for decrease of temperature in connexion with 

 ascending altitude, that any attempted scale or rate of 

 change must he proposed rather as provisional and con- 

 jectural than anj^se certain. It can he offered or 

 received only as an approximation to natural truth. 

 Hourly observations of the thermometer at Inverness 

 and Kingussie, in the years 1838 and 1839, are reported 

 to have given a difference slightly exceeding 2^ of mean 

 temperature for 220 yards of ascent. In even numbers 

 this would seem to indicate a rate or relation of one 

 degree of temperature for something less than 90 j'^ards 

 of ascent in North Britain. Inverness is situate on the 

 coast, and Kingussie at 40 miles inland ; a difference 

 which may rather tend to accelerate the decrease of tem- 

 perature. The recorded mean temperature for Lead-hills 

 in Mid Britain, situate 1280 feet above the sea, is rather 

 under 445-, as observed at 6 and 1 o'clock, and corrected 

 for the slight excess of those two hours together over the 

 averages dedcced from the half-hourly registers at Leith 

 Fort. The assumed sea-level temperature for the latitude 

 may be called 47| ; thus giving about 3|- for the fall of 

 the thermometer in 1280 feet; being at the rate of one 

 degree of temperature for 306 feet, or one of temperature 

 for 122 yards. It has been reported that the difference 

 in the mean annual temperatures at Bj^veU and Allen- 

 heads, in Northumberland, respectively at 50 and at 1360 

 feet of elevation above the level of the sea, amounts to 

 4.7 of Fahrenheit. This fall of the thermometer, for a 

 height of 1310 feet, is equal to one degree of temperature 

 for 278 or 279 feet of ascent. 



According to Mr. John Welsh, the following average 

 results in feet are equivalent to one degi-ee of Fahrenheit, 



