316 
Agricultural Meteorology. 
willi our own. Even within the cereal zone, — i. e. that which 
enjoys greater stabihty of seasons than those of the vine and olive 
lands — there are greater vicissitudes of heat and moisture than in 
England. Take for instance the occurrence of hoar-frosts, so 
destructive in their effects on our early garden produce in the 
spring. The mean number of these at Orange is I7'7, while at 
Rome, where they have been known to occur in June, it is 63'8. 
The buds of vines and mulberries are destroyed by them as fre- 
quently as our peach blossoms in England. In Italy, a district 
round Otranto is ironically called the Land of Flowers, since the 
recurrence of these visitations so often prevents their being suc- 
ceeded by fruit. When the average returns of these phenomena 
are known for any particular locality, the probable loss its crops 
may sustain from that cause may be calculated. Acting upon 
these acquired data, and finding that at Orange, In the 17 years 
between 1813 and 1830, there have been 4 white frosts at the end 
of April or the beginning of May after the leaves of the mulberry 
had appeared, M. Gasparin infers that this is a liability which 
may be apprehended once in 5 years ; and further, since expe- 
rience shows that its occurrence causes a loss of one-fourth of the 
crop, the whole risk (l-5th of the time x 1 -4th of the crop) is 
equivalent to an annual diminution of l-20lh. 
This takes place In the plain of Orange, lying in the centre of 
the great valley of the Rhone, and which is rather favourably 
situated; other localities, not very distant, are far worse off", as 
at Lavaur, where it occurs every three years. 
The effects, indeed, of cold on vegetation must be considered 
under three different heads : first, its intensity ; second, its dura- 
tion ; third, the period of its occurrence. It is this last unseason- 
able condition which renders a small descent below the freezing 
point in the spring so pernicious to the vegetation, which is then 
full of sap In movement. The decrease of temperature at this 
season Is owing mainly to the radiation from earth into space. 
Wherever the atmosphere is habitually clear, the maximum of 
temperature differs more from the minimum than In those which 
are habitually clouded. The clear sky favours the nocturnal 
radiation of that heat from the earth, which, owing to the same 
cause, the sun has Imparted to it in the course of a bright day. 
The distribution of caloric all over the globe is far from being 
governed by the parallels of latitude. The degree of cold in the 
winter will be mainly affected by the humidity or dryness of the 
atmosphere. The oceanic or insular climate, more or less 
common to the whole of the British Islands, but particularly to 
be remarked on their western coasts, condensing the humid vapours 
that have swept over the Atlantic, tends to modify the heat of 
summer, and to diminish the cold in winter. Lines of isothernal 
