156 IV. CLIMATE. 



maritime position of the four last-mentioned places may 

 induce slightly higher means for the year, than would be 

 found at more inland places in the same latitude. 



On putting together the preceding figures, and also 

 those for several other places not specially mentioned 

 here, it appears that half a degree of Fahrenheit's scale, 

 to one whole degree of latitude, will fairly enough repre- 

 sent the rate of decrease in temperature, when traced 

 from south to north. By assuming this rate of decrease 

 to be even and uniform, it becomes applicable as a rule 

 towards estimating the climate for plants comparatively 

 with each other. And further, on the grounds before 

 adverted to, it has been assumed that fifty may be about 

 the mean temperature on the latitudinal line of 51, at the 

 level of the sea. A starting figure, and a rate of decrease 

 northward, being so obtained, the mean annual tempera- 

 ture of the island, in its relation to latitude, and for places 

 at or reduced to the sea-level, may be set forth thus : — 



Lat. 61. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 



Temp. 50. 49^. 49. 48|-. 48. 47^. 47. 46|-. 46. 45^. 45. 

 The half degrees of latitude will correspond with the 

 quarter degrees of temperature. And if it be wished to 

 avoid smaller fractions or decimals, in applying this scale 

 to botanical purposes, all localities may be regarded as if 

 Under the even geographical line of latitude, or the inter- 

 mediate half degree, to which they are nearest. The 

 errors of mis-position in this way could never exceed 

 fifteen geographical miles ; while those of temperature 

 could at most amount to only one-eighth of a degree, in 

 variation from the standard scale, or less than the pro- 

 bable fallacies of the scale itself. 



Along the south coast of England, the changes of tem- 

 perature almost cease to be questions of latitude ; rather 

 becoming those of longitude and increased insularity ; 



