246 PHYSICS. 
torrid zone during the rainy season (especially at the beginning and end). 
They here succeed each other almost daily at the times of maximum heat, 
while the lightning appears to be sharper as well as more luminous than in 
more temperate regions. With respect to the annual distribution of 
thunder and lightning in higher latitudes, the cornparisons of Kaemtz show. 
that thunder storms occur on an average about nineteen or twenty times 
each year in France, Holland, and Germany. Of these most take place in 
summer, the relative proportion in Germany being sixty-six per cent. in 
summer, twenty-four and a half in spring, eight in autumn, and one and a 
half in winter. In Russia and other interior portions of the old world, 
winter thunder storms are entirely wanting; there are seventy-nine per 
cent. in summer, sixteen in spring, and five in autumn; the total number 
appears to be less than in Germany and France. In Scandinavia the 
number of thunder storms is still less, continually decreasing towards the 
north. In the highest northern regions whole years elapse without thunder. 
being once heard. On the west coast of Norway, particularly in the 
bishopric of Bergen, where about six thunder storms occur in the year, the 
winter storms predominate, these on the other hand being entirely wanting 
in Sweden. In Iceland, also, and on the western coast of North America, 
the winter thunders are most numerous; the Faroes, the Hebrides, and the 
Shetland Islands, not being entirely free from them. In Germany summer 
and winter thunders are distinguished by the greater poverty of lightning 
in the latter, and in frequently accompanying regular storms, while the 
former almost always arise in calm weather. Thunder and lightning are 
especially prevalent in mountainous regions, where a peculiar phenomenon 
is presented in this respect, namely, that a mountain crest or peak often 
forms a dividing line, beyond which such weather does not pass. Wooded 
mountains seem better adapted than bald for this purpose. It is especially 
the case, where a valley divides into several branches, a steep mountain 
standing in the forks of division, that storms coming up the valley often tarry 
about the mountain, and subsequently divide. 
On Lightning Rods. 
A lightning rod is a contrivance invented by Franklin for conducting a 
stroke of lightning over or along a building or object of any kind, without 
any of the terrible effects of this powerful agent being exhibited. As light- 
ning always follows the best conductor, it is very reasonable to suppose that 
a continuous rod of metal, of sufficient thickness, would carry it over a 
certain space without producing any injury to the poorer conductors in the 
immediate vicinity. Another suggestion of Franklin, that the electricity of 
a cloud may be silently drawn off by a pointed conductor, and a stroke thus 
averted, met with a great many opponents. It has been especially objected 
that the points of lightning rods, from their small extent and surface, must 
be incapable of carrying off a powerful discharge without injury ; in fact, it 
has not rarely been found that they have actually been melted, and even the 
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