with Geographic Botany. — Temperature. 181 



northern ; yet the total amount of the mean maximum tem- 

 peratures of each throughout the year would in all probability 

 be very similar. Under these conditions vegetation appears 

 not to thrive so well as where the seasons are subject to ex- 

 tremes : thus the southern lands are almost destitute of a 

 plant where the north of Europe supports a tolerable vege- 

 tation. 



Along the margins of continents there are portions of the 

 surface which experience the effects of the ocean, whilst be- 

 yond this in the interior a continental climate is retained. 

 These strips have a modification of climate holding a station 

 between continents and islands : their temperature is of 

 course governed by the region of waters flowing around them, 

 and are also exposed to vicissitudes from the interior. Mr. 

 Kirwan has made an estimate of the progression of tempera- 

 ture in these cases ; for every fifty miles from the sea he 

 states the annual mean to be affected according to the lati- 

 tude as follows : — 



From latitude 70° to 35° cooled \ of a degree. 



35 ... 30 ... \ 



30 ... 25 warmed \ 



25 ... 20 ... i 



20... 10 ... 1° 



Malte-Brun, though he has treated the effects of aspect 

 with considerable happiness, has hardly distinguished the in- 

 fluence of the direction of a surface, apart from its inclination, 

 with sufficient accuracy. Aspect expresses the direction of a 

 surface in regard to the sun ; to have a good aspect is to hold 

 one opposite to its midday rays. At the same time, inclina- 

 tion of surface must not be overlooked, for presently we shall 

 show that it materially influences the temperature. Every 

 mountain range displays a crowd of instances of its effects on 

 the vegetable kingdom, on the habits of animals, and the mi- 

 gration of man. To prevent any unnecessary repetition of 

 words, we shall confine our attention to the circumstances of 

 inclination and direction of surface in the northern hemi- 

 sphere ; and on reconsidering this subject in the southern, 

 the same causes will be found active, with the only necessary 

 allowance for the opposite situation of the sun. 



A mountain may be imagined with four sides, the direction 

 of whose aspect is such that they regard the four points of 

 the compass, east, west, north, and south. Suppose, further, 

 that these sides have a regular slope or inclination, which we 

 shall place at 45 degrees. At sun-rise in the morning the 

 rays of heat will strike on the east side, making an allowance 



