u6 



BOTINICAL GAZETTE. 



Colorado Springs, where the difference of elevation is more than 

 8,000 feet, tlie change is 1° for each 295 feet. In the case of Alt. 

 Washington and Shelburne, New Hampshire, it is 325 feet for each 

 degree. The former case is the most favorable in every respect, and 

 a> most oi our results are drawn from the western region, I have 

 adopted, as a round number, 300 feet. 



Now. if the average mean annual temperature all around the 

 base of a mountain were known, it would be a very simple mat- 

 ter to determine, with some accuracy, the temperature at timber 

 line, knowing its height and the un an height of its base. The 

 nearest approach which can be made to this, is to assume that the 

 station or stations at or near the base, represent the average 

 climite, a supposition which, in many cases, is by no means correct. 

 Using, however, in the manner indicated, such data as are at hand, 

 I have obtained the following results: 



The mean of these results is 30.4°, and this is probably very 

 near the true mean annual temperature of the timber line. The 

 better the conditions of the determination, the nearer are the results 

 to this mean. Mts. Blackmore and Bridger are very good cases, 

 being on the border of the Gallatin Valley, in which Fort Ellis is 

 situated, and but very few miles distant from the latter. Mts. 

 Lincoln and Silverheels are also admirably situated with respect to 

 Fairplay, but the annual temperature of the latter station is not 

 well determined. Pike's Peak and Colorado Springs make an 

 excellent pair of stations, being but ten miles apart, and the annual 

 temperature at the latter place being well determined by the obser- 

 vations of the Signal Bureau. On the other hand, Mt. Powell and 

 the White River Agency are widely separated by man}^ miles of 

 high plateaus, which may materially change the conditions of the 

 temperature about the mountain. 



