with Geographic Botany. — Temperature. 18? 



Avill yield a mean of 336*33 feet of elevation for every degree 

 of depression in the thermometer. Those obtained in Great 

 Britain have the mean of 234*50 feet for the same ; and the 

 two combined give 285*41 feet. By applying these means 

 as a correction for the elevation of any place where the mean 

 temperature has been accurately observed, and thus finding 

 the mean temperature of the base at the level of the sea, it 

 will only be necessary to compare the latter with the mean 

 temperature in Leslie's table to ascertain their correctness. 

 The Hospice of St. Gothard is fixed at an elevation of 6390 

 feet, and the mean temperature of the year is 30°*4 ; with the 

 correction it will be 49° at the base, whilst the latitude of St. 

 Gothard by the table gives a mean of 57°*6. Again, Berne is 

 situated at 1650 feet, and has a mean temperature of 49°*2; 

 the base will be 53°*9 by the correction, and by the table 

 57°*2. The corrections here applied are from the mean of 

 the European continent, as being the situation both of the 

 experiments and of the examples, and the results can hardly 

 be considered as approximations. With the mean of Great 

 Britain a greater correctness is apparently obtained, making 

 the mean temperature of the bases respectively 57°*7 and 

 56°*3. 



Another illustration taken from an extremely interesting 

 spot will suffice. The city of Quito occupies a plain raised 

 to 9500 feet, and surrounded by numerous volcanoes ; among 

 them are Chimborazo, Antisana, and Pichincha, with many 

 others equally stupendous but less known. Its mean annual 

 heat is 67°, and is situated only 13' from the equator. In 

 this instance we shall use the correction for the height given 

 by Humboldt for the Andes, and take that for the elevation 

 of Quito. This mean, so much above the European, will be 

 mentioned presently ; at present we find it to make the base 

 of Quito enjoying a mean of 89°*4. The equatorial mean has 

 been already dwelt upon ; and though this surpasses it by 

 some degrees, yet some allowances for the difference will be 

 justified on the same grounds, that the elevated plains of 

 Thibet extend the usefulness of the northern aspect of the 

 Himma-leh mountains. 



Thus the decrease of temperature on elevation does not 

 take place uniformly, nor does it occur in the same ratio in 

 the equatorial and in the temperate zones. Humboldt, whose 

 opportunities of multiplying facts at great elevations have 

 been so unbounded, found that the progression was very ir- 

 regular among the Cordilleras. His observations reduced to 

 English feet stand thus : — 



02 



