Page:Philosophical Transactions - Volume 054.pdf/309



experience, since the discovery by Dr. Franklin, has now established a truth amongst philosophers, that lightening, like the electric fluid, passes more freely through iron, copper, and other metals, than through dry wood, stone, or marble.

Instances of this truth are innumerable: and to convince us thereof, we need only trace the late violent effects of lightening on St. Bride's Church, and the houses in Essex-street, &c.

For, upon examining these buildings, it appears, that there are certain thick bars of iron, through which the lightening has past, without producing any visible effects: and on the contrary, in certain parts where the junctions of those bars with the stone, or wood, are made, there the lightening, rushing from the iron, has broke the stone to pieces, and shivered the wood.

From the like experience we also learn, that if the iron is too slender for conducting the lightening, it is either dashed into pieces, or exploded like gunpowder; just in the same manner as we are able, by the electric power, to break and dissipate in vapour a very slender wire. Bars of metal, of a proper thickness, and conveniently disposed, seem therefore necessary for the securily of such buildings.

It is to be noted, that the mischiefs caused by lightening are not always owing to its direction from the clouds to the buildings or other eminences, and thence