5> 

 5> 



100 IV. CLIMATE. 



as deduced from observations of the thermometer during 

 four balloon ascents ; the first and fourth relating to 

 heights up to 4000 feet, the second and third respectively 

 to 7000 and 2700 feet :— 



August 17, average 277.9 feet. 



26, „ 281.8 

 October 21, „ 279.3 

 November 10, „ 266.0 „ 

 Whether the average of these four figures, 276 feet or 92 

 yards, will correctly represent the mean annual decrease 

 of temperature in connexion with ascending altitude, near 

 the surface of the ground, it is yet impossible to say. In 

 making observations with the barometer and sympieso- 

 meter, in order to ascertain the altitudes at which plants 

 were found on the mountains of Britain, the writer of this 

 volume had constant occasion to note the temperature of 

 the air. Many of these notes still exist ; but as they are 

 not simultaneous for different altitudes, they cannot be 

 relied upon as very exact or serviceable data in the matter 

 under present consideration. They appear on a rough 

 average to indicate less than 100 yards of ascent for a de- 

 crease of one of temperature by the thermometer of 

 Fahrenheit. Mr. Galbraith reduced the rate of decrease 

 to 70 yards for one degree of temperature. Professor 

 Leslie deemed 100 yards nearer the truth. 



The temperatures of spring water may afford some 

 additional data towards showing a rate of decrease in 

 connexion with ascending altitude. The temperature of 

 spring water at Lead-hiUs is stated to be 44, at an alti- 

 tude of 1280 feet. The mean of two springs at Colin- 

 ton, near Edinburgh, at 290 feet of mean altitude is re- 

 ported to be something over 47^ ; being rather more than 

 3g difference of temperature for nearly 1000 feet of ascent, 

 say one degree of the thermometer for 280 feet or 93 



