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 fluid 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 years 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.

Ex. 1. A is a board (Pate VIII. Fig. 19.) representing the gable end of a house: it fixed on another board в: a b c d is a square hole, to which a piece of wood is fitted; a d represents a wire fixed diagonally on the wood a b c d x b terminated by a knob x, represents a weathercock, and the wire cz is fixed to the board A.

It is evident that in the state in which it is drawn in the figure, there is an interruption in the conducting rod; accordingly, if the chain m is connected with the outside of a Leyden phial, and then that phial is discharged through x, by bringing one part of the discharging rod to the knob of the Leyden phial, and the other to within an inch or two of x, the piece of wood a b c d will be thrown out with violence.

James. Are we to understand by this experiment, that if the wire x b had been continued to the chain, that the electric fluid would have run through it without disturbing the loose board?

Tutor. Ex. 2. Just so; for if the piece of wood be taken out, and the part a be put

to the place b, then d will come to c, and the conducting rod will be complete, and continued from through b c to z, and now the phial may discharged as often as you please, but the wood will remain in its place, because the electric fluid runs through the wire to z, and makes its way by the chain to the outside of the phial.

Charles. Then if x be supposed the weathercock of the church, the lightning having overcharged this, by its endeavours to reach another conductor, as c z, forced away the stone or stones represented by a b c d ?

Tutor. That is what I meant to convey to your minds by the first experiment; and the second shows very clearly that if an iron rod had gone from the weathercock to the ground, without interruption, it would have conducted away the electricity silently, and without doing any injury to the church.

James. How was it that all the stone were not beaten down?

Tutor. Because, in its passage down