330 
AjricuUural Meteorology. 
three or four years; others every year; and in the afternoon 
rather than the forenoon. " Often," says M. Desperre,* "the 
hail-bearing column of cloud issues by some gorge or defile ;" 
and adds that it is suspected that this phenomenon has occurred 
jnore frequently of late years, since those defiles were stripped of 
the forests which once crowned their summits. De la Rive's 
opinion M. Gasparin thinks well-founded — that the formation of 
hail and the development of electricity are referable to a common 
cause — the result of the meeting of two currents of air of different 
temperatures from opposite quarters of the heavens. " The hail- 
bearing column will sometimes be deflected by an elevation — be 
precipitated into a valley — as it comes from the meeting of a 
warm wind (in most parts the south-west) with a cold one, it 
would follow that those districts which are protected towards the 
south-west by a chain of hills will suffer less than others exposed 
to that quarter. There were in the Piedmontese dominions, in 
1840, the following number of storms: — 
Savoy. Piedmont. Liguria. 
39 . . 103 . . 47 
Of which 34 . . 61 . . 18 
fell in the months of June, July, and August. 
Their geographical distribution appears to favour the conjecture 
advanced by M. Gasparin — the smallest number occurring in 
Savoy, where the great barrier of the Alps would check the arrival 
of the south-west winds ; the greatest in Piedmont, which is most 
open to that quarter. Liguria has an intermediate number ; though 
exposed to the south-west, and extended along the Apennines, 
the influence of the sea air probably tempers those sudden changes 
that happen elsewhere. 
We collect from this work some curious particulars respecting 
the rains, which occur most plentifully in regions to the southward, 
and westward of mountainous ranges, and the more so the nearer 
those ranges are to the great reservoirs of humidity : they diminish 
in the lands of plains. The central and southern portion of 
Europe has more rain in summer than in the autumn, until the 
parallel of the British islands is reached, where the chief fall is 
in the autumn. 
The quantity of rain is of less consequence than the frequency 
Avith which it occurs, and the periods over which it is spread. At 
Lancaster, Penzance, and '^J'ruro there are commonly 159-5 daysf 
in the year in which it rains; along the coast of France 139-7; 
* In a paper read before the Royal Academy of Turin, 1844. 
t M. Gasparin does not state his authority for this. Howard's ' Climate 
of London,' i. p. 103, pives, as the mean of twenty years, 178 rainy days for 
the neighbourhood of London. 
