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neatly with tin foil: x is a glass handle fixed to a socket, by which the upper plate is removed from the under one.

Charles. What do you mean by an electrophorus ?

Tutor. It is, in fact, a sort of simple electrical machine, and is thus used. Rub the lower plate в with a fine piece of new flannel, or with rabbit's, or hare's, or cat's skin, and when it is well excited, place upon it the upper plate A, and put your finger on the upper plate: then remove this plate by the glass handle x, and if you apply your knuckle, or the knob of a coated jar, you will obtain a spark. This operation may be repeated many times without exciting again the under plate.

James. Can you charge a Leyden jar in this way?

Tutor. Yes, it has been done, and by a single excitation, so as to pierce a hole through a card.

Here is another kind of electrometer (Plate VIII. Fig. 18.) which is by far the most sensible that has been yet invented;

that is, it is capable of discovering the smallest quantities of electricity. A is a glas jar, B the cover of metal, to which are attached two pieces of gold leaf x, or two pith-balls suspended on threads: on the sides of the glass jar are two narrow strips of tin foil.

Charles. How is this instrument used?

Tutor. Any thing that is electrified is to be brought to the cover, which will cause the pieces of gold leaf, or pith-balls to diverge; and the sensibility of this instrument is so great that the brush of a feather, the throwing of chalk, hair-powder, or dust, against the cap B, evinces strong signs of electricity.

Ex. 5. Place, on the cap в, a little pewter, or any other metallic cup, having some water in it: then take from the fire a live cinder, and put it in the cup, and the electricity of vapour is very admirably exhibited.

A thunder-cloud passing over this instrument will cause the gold leaf to strike the sides at every flash of lightning.

Ex. 6. I will excite this stick of sealing-wax and bring it to the cover B: you see how often it causes the gold leaf to strike against the sides of the glass.

James. Are the slips of tin foil intended to carry away the electric fluid communicated by the objects presented to the cap B?

Tutor. They are; and by them the equilibrium is restored.

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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

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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;

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