478 APPENDIX. 



have a contrary direction — that is, incline to the north- 

 eastward, — which is attributed to the low summer tem- 

 perature along the coast. 



In North America, the decrement of the mean 

 annual temperature incident to the increase of latitude 

 is much greater than in Europe ; and there is also, 

 especially in the interior, a much wider difference 

 between the summer heat and winter cold, — the 

 increase of vernal heat being sudden and great. On 

 the north shore of Lake Huron, which is nearly in the 

 same parallel with the bottom of the Gulf of Venice, 

 the snow covers the ground for nearly half the year ; 

 though the mean heat of the three summer months, 

 amounting to 70° of Fahrenheit's scale, equals that ex- 

 perienced at Bourdeaux. Cumberland House, having 

 the same latitude with the city of York in England, 

 stands on the isothermal line of 32°, which in Europe 

 rises to the North Cape in latitude 71°; but its summer 

 heat exceeds that of Brussels or Paris. Humboldt in- 

 forms us that, in countries whose mean temperature is 

 below 63°, spring, or the renewal of vegetation, takes 

 place in that month which has a mean heat of 33° or 

 34°, and deciduous trees push out their leaves when 

 the mean reaches to 52° ; thus, the sum of the tempe- 

 ratures of the months which attain the latter heat fur- 

 nishes a measure of the strength and continuance of 

 vegetation. Lake Huron, in latitude 44°, enjoys five of 

 these months ; Cumberland House, three ; and Bear 

 Lake and Fort Enterprise, both in latitude 64J°, only 

 two : all these places have an interior or continental 

 climate. At Winter Island, on the eastern coast, in 

 latitude 64^°, and at Igloolik, in latitude 66%°, no month 

 in the year attains a mean heat of 52°; and at Churchill, 

 in latitude 59°, the summer heat does not exceed that 

 of Bear Lake, being 10° less than that which is ex- 



