Dr. Franklin has demonstrated the iden-tity of thunder with the electric explosion. He availed himself of many curious discoveries which he had made of electrical laws: in particular, having observed that electricity was drawn off at a great distance, and without the least violence of action, by a sharp metallic point, he proposed to philosophers to erect a tall mast or pole on the highest part of a building, and to furnish the top of it with a fine metallic point, properly insulated, with a wire leading to an insulated apparatus for exhibiting the common electrical appearances. To the whole of this contrivance he gave the name of Thunder Rod, which it still retains. He had not a proper opportunity of doing this himself, at the time of his writing his dissertation in a letter from Philadelphia to the Royal Society of London; but the contents were so scientific, and so interesting, that in a few weeks they were known over all Europe. His directions were followed in many places. In particular, the French academicians, encouraged by the presence of their monarch, and the great satisfaction which he expressed at the repetition of Dr. Franklin's most instructive experiments, which discovered and made known the theory of positive and negative electricity, as it is now received, were eager to execute his orders, and make his grand experiment, which promised so fairly to bring this tremendous operation of nature, not only within the pole of science, but in the management of human power. But in the mean time, Dr. Franklin, impatient of delay, and perhaps incited by the honourable desire of well-deserved fame, put his own scheme in practice. His inventive mind suggested to him a method of presenting a point to a thunder cloud at a considerable distance. This was, by fixing his point on the head of a paper kite, which the wind should raise to the clouds, while the wet string that held it should serve for a conductor of the electricity. With a palpitating heart, Dr. Franklin, unknown to his neighbours, and accompanied only by his son, went into the fields, and sent up his messenger that was to bring him news from the heavens. He obtained only a few sparks from his apparatus that day; but returned to his house in a state of perfect satisfaction with his success. We may justly consider this as one of the greatest of philosophical discoveries, and as doing the highest honour to the inventor; for it was not a suggestion from an accidental observation, but arose from a scientific comparison of facts, and a sagacious application of the doctrine of positive and negative electricity; a doctrine wholly Dr. Franklin s, and the result of the most acute and discriminating observation. It was this alone, that suggested the whole; and, by explaining to his satisfaction the curious property of sharp points, gave him the courage to handle the thunderbolt of the heavens. It is now a point fully ascertained, that thunder and lightning are the electric snap and spark, as much superior to our puny imitations as we can conceive from the immense extent of the instruments in the hands of Nature.

If (says Dr. Franklin,) a conductor, one foot thick, and five feet long, will produce such snaps as agitate the whole human frame, what may we not expect from a surface of ten thousand acres of electrified clouds? How loud must be the explosion! how terrible the effects!

To this wonderful discovery, Dr. Darwin alludes in the following lines: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 his shell.

Fire Balls, - are a kind of luminous bodies, commonly appearing at a great height above the earth, with a splendour surpassing that of the moon, and sometimes equalling her apparent size. They generally proceed in this hemisphere from north to south with vast velocity, frequently breaking into several smaller ones, sometimes vanishing with a report, and sometimes not. These luminous appearances, no doubt, constitute one branch of the ancient prodigies, or blazing stars. They sometimes resemble comets, in being attended with a train; but frequently they appear with a round well-defined disk. The first of these, of which we have any accurate account, was observed by Dr. Halley and others, at different places, in 1719. From the slight observations they could take of its course among the stars, its perpendicular height was computed at about seventy miles from the surface of the earth. The height of others has also been computed, and found to be various; though in general it is supposed to be beyond the limits assigned to our atmosphere, or where it loses its refractive power. The most remarkable of these on record appeared on the 18th of August, 1783, about nine o'clock in the evening. It was seen to the northward of Shetland, and took a southerly direction for an immense space, being observed as far as the southern provinces of France and Rome. During its course, it appears frequently to have changed its shape; sometimes appearing in the form of one ball, sometimes two or more; sometimes with a train, sometimes without one. It passed over Edinburgh nearly in the zenith, and had then the appearance of a well-defined round body, extremely luminous, and of a greenish colour; the light which it diffused on the ground giving likewise a greenish cast to objects. After passing the zenith, it was attended by a train of considerable length, which, continually augmenting, at last obliterated the head entirely; so that it looked like a wedge, flying with the obtuse end foremost. The motion was not apparently swift, by reason of its great height; though in reality it must have moved with great rapidity, on account of the vast space it travelled over in a short time. In other places its appearance was very different. At Greenwich, we are told, that "two bright balls, parallel to each other, led the way, the diameter of which appeared to be about two feet; these were followed by an expulsion of eight others, not elliptical, seeming gradually to fall to pieces, for the last was small. Between each two balls a luminous serrated body extended, and at the last a blaze issued, which terminated in a point. Minute particles dilated from the whole. The balls were tinted first by a pure bright light, then followed a delicate yellow, mixed with azure, red, green, etc. which, with a coalition of bolder tints, and a reflection from the other balls, gave the most beautiful rotundity and variation of colours, that the human eye could be charmed with. The sudden illumination of the atmosphere, and the form and singular transition of this bright luminary, contributed much to render it awful: nevertheless, the amazingly vivid appearance of the different balls, and other rich connecting parts, not very easy to delineate, gave an effect equal to the rainbow in the zenith of its glory."