PROFESSOR FORBES ON THE CLIMATE OF EDINBURGH. 359 
A sort of reaction appears in a comparatively limited yet marked excess of tem- 
perature, during the middle fortnight of December. This excess is clearly indicated 
in every one of the four decennial periods. About the 12th May there is also a 
brief depression of temperature, which, so far, appears to confirm the existence of 
the three cold days (11th, 12th, and 15th May) mentioned by Humboldt,* which 
likewise seem to be indicated at Greenwich; but these deductions are of a descrip- 
tion not much to be relied on, and, after all, they most likely depend on causes 
more or less local. 
(2 and 3). On the “fluctuation” of daily mean temperature, and on the 
diurnal range. 
68. If we project, in the form of a curve, the fluctuation of the daily mean 
temperature for forty years included in Mr Aprr’s observations (as shown in 
column 5 of Table XIII.), we find a very remarkable variation with the season of 
the year. There appears to be the least casual fluctuation about the end of July, 
when it amounts to about 16° or 17°, and the maximum occurs nearly six months 
later, or about the middle of January, when it may be reckoned at between 28” 
and 29°. These periods coincide, it will be observed, nearly with the hottest and 
coldest seasons. It may be accidental, but I cannot help remarking, that for 
some days together these values of “ fluctuation” range remarkably low, and 
then for another short period as uniformly high. An example of this may be 
noticed in Table XII. for the latter part of December. 
69. The other element, the diurnal range, or mean daily difference of maxi- 
mum and minimum readings for twenty-nine years, gives us a curve of a nearly 
opposite form to the preceding, and much more regular. The minimum range of 
9°5 occurs in the end of December or beginning of January; the maximum of 
nearly 18° between the middle and end of June. 
Sect. 7. Remarks on the Price of Corn during Fifty-six years, as compared with 
Meteorological Data. 
70. It will be recollected that Sir William Herschel, when investigating the 
connection of the solar spots with terrestrial temperature, employed (though not 
without some reserve, and only in the absence of better data) the price of wheat 
as an indication of the heat or cold of different years. 
71. I thought it might be worth while to test roughly the applicability of 
such a scale of climate; and I even considered that it might be practicable to 
express the relation of the abundance of corn to the meteorological elements 
which might be expected chiefly to influence it. These expectations signally 
failed. But I think it may be instructive to record the failure, at a time when 
agriculturists are directing their attention to meteorology. 
* Cosmos, vol. i. note 86. 
