IV. EXPLANATIONS. 345 



tbe two lines of figures, which it may be well here to set right. On 

 comparing the extreme temperatures for the whole of Britain, the south 

 coast of England with the summits of the northern hills, the rate of 

 decrease adapted to the centigrade scale will be found slower or less 

 than that adapted to the Fahrenheit scale. But in looking to latitude 

 exclusively, apart from elevation, the reverse holds true ; the rate of 

 decrease by the centigrade scale being made very slightly quicker (not 

 " slower or less ") than that given as adapted to the thermometer of 

 Fahrenheit. The reader is requested to make this correction with his 

 pen, on page 158, by erasing the words " slower or less than," and 

 introducing the words " in excess over" in their place. The difference, 

 however, is very slight. The two scales begin on perfect equality, as 50 

 fahr. and 10 cent., in latitude 51. Northwards from thence the latter 

 gradually increases on the former; so that, in latitude 61, we place 45 

 fahr. and 7 cent, as if equal ; the true correspondence being 45 fahr. 

 and 7.22 cent, as above shown. So nearly equal are the two rates, that 

 ten degrees of latitude do not raise the difference to a quarter of a 

 degree of temperature by centigrade scale. These remarks on the indi- 

 cations of temperature are applicable to the three subdivisions of the 

 general list. In some other respects the explanations are better given 

 separately for each subordinate division. 



1. Upper limits on the Grampian Mountains. — The names of the 

 plants here succeed each other in accordance with the three (or fewer) 

 figures which terminate the lines. Those figures show the highest 

 spots at which the plants have been noted by the author; with some 

 few additions from other sources, mostly distinguished by inverted 

 commas or other indications. The highest spots being equal for two or 

 more species, then the second or the third figure is taken to determine 

 their relative places in tbe list. The heights for the Hieracia, quoted 

 between inverted commas, as " 1400," and followed by the initial letter 

 B, are taken from Mr. Backhouse's Monograph of the genus before 

 mentioned, on page 3 and elsewhere. In the latter portions of the list, 

 where the same figures for temperature and altitude apply to numerous 

 species, some needless repetition of them is avoided by their conversion 

 into head-titles of sections. 



The basis of the list here printed for the Grampians, was originally 

 published in the first volume of the Lonclon Journal of Botany, for the 

 year 1842, pages 62 to 72. Since that date other hills have been 

 VOL. IV. 2 Y 



