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 and expensive however, to wish to see often repeated.

If the erecting of an apparatus of this sort should become general in countries where thunder storms are frequent and often attended with mischief, though damage should really be averted by it, the operation of the apparatus would be unseen, and therefore unknown, unless in such rare instances as that mentioned by Mr. Kinnersly. To make its effects apparent, as has been hinted to me by Dr. Heberden, a very deservedly eminent physician here, if chains are employed as metallic communications, instead of wires or rods, whenever the lightning comes near enough to affect the apparatus in a considerable degree, it will without mischief be visible in the dark, by its sparkling and snapping in its passage, at the links of the chain.

The effects of the apparatus may be observed in another manner. If the metallic communications are by the means of a wire or single rod, there may be, in some part of its length, in any place convenient for observation, a space left where the metal is discontinued; but this space should not exceed two inches. The two extremities of the metal at this interruption should be furnished with brass knobs not less than an inch in diameter. By this method, though the effects of the apparatus would not be considerably lessened, they might be observed. For at times, when no lightening was visible, but when clouds replete with it came near the apparatus, or rain from them fell upon it, there would be a snapping from one of the brass knobs to the other. When indeed the lightning was near, there would not only be this snapping; but, if the cause was great, a stream of fire would be Rh