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CONVERSATION XXXIX.

Of Atmospherical Electricity.

CHARLES. You said yesterday, that the electrometer was affected by thunder and lightning: are lightning and electricity similar?

Tutor. They are, undoubtedly, the same fluid ; and they are the same, was discovered by Dr. Franklin more than half a century ago.

James. How did he ascertain this fact?

Tutor. He was led to the theory from observing the power which uninsulated points have in drawing off the electricity from bodies. And having formed his system, he VOL. III.

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was waiting for the erection of a spire, in Philadelphia, to carry his views into execution, when it occured to him that a boy's kite would answer his purpose

better than a spire. He therefore prepared a kite, and having raised it, he tied to the end of the string a silken cord, by which the kite was completely insulated. At the junction of the two strings he fastened a key as a good conductor, in order to take sparks from it.

Charles. Did he obtain any sparks?

Tutor. One cloud, which appeared like a thunder-cloud, passed without any effect; ; shortly after, the loose threads of the hempen string stood erect, in the same manner as they would if the string had been hung on an electrified insulated conductor. He then presented his knuckle to the key, and obtained an evident spark. Others succeeded before the string was wet, but when the rain had wetted the string, he collected the electricity very plentifully:

-Led by the phosphor light, with daring tread,
Immortal Franklin sought the fiery bed ;

Where, nurs’d in night, incumbent tempest shrouds
The seeds of thunder in circumfluent clouds
Besieg'd with iron points his airy cell,
And pierc'd the monster slumb'ring in the shell.

DARWIN.

James. Could I do so with our large kite?

Tutor. I hope you will not try to raise your kite during a thunder storm, because, without very great care, it may be attended with the most serious danger. Your kite is however quite large enough, being four feet high, and two feet wide : every thing depends on the string, which, according to Mr. Cavallo, who has made many experiments on the subject, should be made of two thin threads of twine, twisted with a copper thread. And to Mr. Cavallo's work on electricity, vol. 11. such persons as are desirous of raising kites, for electrical purposes, should be referred, in which they will find ample instruction.

Charles. How do the conductors, which I have seen fixed to various buildings, act in dispersing lightning ?

Tutor. You know how easy it is to charge a Leyden jar: but if, when the machine is at work, a person hold a point of steel, or other metal, near the conductor, the greater part of the Auid will run away by that point instead of proceeding to the jar. Hence it was concluded that pointed rods would silently draw away the lightning from clouds passing over any building.

James. Is there not a particular method of fixing them?

Tutor. Yes : the metallic rod must reach from the ground, or the nearest piece of water, to a foot or two above the building it is intended to protect, and the iron rod should come to a fine point. Some electricians recommend that the point should be of gold, to prevent its rusting.

Charles. What effects would be produced, if lightning should strike a building withot a conductor?

Tutor. That may be best explained, by informing you of what happened, many prars ago, to St. Bride's church. The light

ning first struck the weathercock, from thence descending in its progress, it beat out a number of large stones of different heights, some of which fell upon the roof of the church, and did great damage to it. The mischief done to the steeple was so considerable, that eighty-five feet of it was obliged to be taken down.

James. The weathercock was probably made of iron, why did not that act as a conductor ?

Tutor. Though that was made of iron, yet it was completely insulated by being fixed in stone, that had become dry by much hot and dry weather. When therefore the lightning had taken possession of the weather-cock, by endeavouring to force its way to another conductor, it beat down whatever stood in its way.

Charles. The power of lightning must be very great,

Tutor. It is irresistible in its effects; the following experiment will illustrate what I have been saying

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