LIGHTNING. It is now universally allowed, that lightning is really an elec trical explosion or phenomenon. Philoso phers had not proceeded far in their ex periments and inquiries on this subject, before they perceived the obvious analogy between lightning and electricity, and they produced many arguments to evince their similarity. But the method of prov ing this hypothesis, beyond a doubt, was first proposed by Dr. Franklin, who, about the close of the year 1749, con ceived the practicability of drawing light ning down from the clouds. Various cir cumstances of resemblance between light ning and electricity were remarked by this philosopher, and have been abun dantly confirmed by later discoveries, such as the following : Flashes of light ning are usually seen crooked and waving in the air ; so the electric spark drawn from an irregular body at some distance, and when it is drawn by an irregular body, or through a space in which the best con ductors are disposed in an irregular man ner, always exhibits the same appearance. Lightning strikes the highest and most pointed objects in its course, in prefe rence to others, as hills, trees, spires, masts of ships, &c. so all pointed conduc tors receive and throw off the electric fluid more readily than those that arc terminated by flat surfaces. Lightning is observed to take and follow the readiest and best conductor ; and the same is the case with electricity in the discharge of the Leyden phial : from whence the Doc tor infers, that in a thunder-storm it would be safer to have one's clothes wet than dry. Lightning burns, dissolves metals, rends some bodies, sometimes strikes persons blind, destroys animal life, deprives magnets of their virtue, or reverses their poles ; and all these are well-known properties of electricity.
To demonstrate, however, by actual experiment, the identity of the electric fluid with the matter of lightning, Dr. Franklin contrived to bring lightning from the heavens by means of a paper kite, properly fitted up for the purpose, with a long fine wire string, and called an electrical kite, which he raised when a thunder storm was perceived to be com ing on : and with the electricity thus ob tained, he charged phials, kindled spirits, and performed all other such electrical experiments as are usually exhibited by an excited glass globe or cylinder. This happened in June, 1752, a month after the electricians in France, in pursuance of the method which he had before pro posed, had verified the same theory, but without any knowledge of what they had done. The most active of these were Messrs. Dalibard and Delor, followed by M. Mazeas, and M. Monnier.
Nor had the English philosophers been inattentive to this subject. Mr. Canton, however, succeeded in July, 1752; and in the following month Dr. Bevis and Mr. Wilson observed nearly the same appear ances as Mr. Canton had done before. By a number of experiments Mr. Canton also soon after observed, that some clouds were in a positive, while some were in a negative state of electricity : and that the electricity of his conductor would some times change from one state to the other five or six times in less than half an hour.
How it happens that particular parts of the earth, or the clouds, come into the op posite states of positive and negative elec tricity, is a question not absolutely deter mined : though it is easy to conceive that when particular clouds, or different parts of the earth, possess opposite electricities, a discharge will take place within a cer tain distance ; or the one will strike into the other, and in the discharge a flash of lightning will be seen. Mr. Canton
queries whether the clouds do not be come possessed of electricity by the gradual heating and cooling of the air ; and whether air suddenly rarefied may not give electric fire to clouds, and va pours passing through it, and air suddenly condensed receive electric fire from them. Mr. Wilcke supposes, that the air con tracts its electricity in the same manner that sulphur and other substances do, when they are heated and cooled in con tact with various bodies. Thus, the air being heated or cooled near the earth, gives electricity to the earth, or receives it from it ; and the electrified air being conveyed upwards by various means, communicates its electricity to the clouds. Others have queried, whether, since thunder commonly happens in a sultry state of the air, when it seems charged with sulphureous vapours, the electric matter then in the clouds may not be generated by the fermentation of sul phureous vapours with mineral or acid vapours in the air. With regard to places of safety in times of thunder and light ning, Dr. Franklin's advice is, to sit in the middle of a room, provided it be not un der a metal lustre suspended by a chain, sitting on one chair, and laying the feet on another. It is still better, he says, to bring two or three mattresses, or beds, into the middle of the room, and folding them double, to place the chairs upon them ; for as they are not so good con ductors as the walls, the lightning will not be so likely to pass through them. But the safest place of all is in a hammock hung by silken cords, at an equal dis tance from all the sides of the room. Dr. Priestley observes, that the place of most perfect safety must be the cellar, and es pecially the middle of it ; for when a per son is lower than the surface of the earth, the lightning must strike it before it can possibly reach him. In the fields, the place of safety is within a few yards of a tree, but not quite near it. Beccaria cautions persons not always to trust too much to the neighbourhood of a higher or better conductor than their own body, since he has repeatedly found that the lightning by no means descends in one undivided track, but that bodies of various kinds conduct their share of it at the same time, in proportion to their quantity and conducting power. See Franklin's Letters, Beccaria's Lettre deli' Ellettri cessimo, Priestley's History of Electricity, and Lord Mahon's Principles of Electri city.
Lord Mahon observes, that damage may be done by lightning, not only by the main stroke and lateral explosion, but also by what he calls the returning stroke, by which is meant the sudden and violent return of that part of the natural share of electricity which had been gradually ex pelled from some body or bodies, by the superinduced elastic, electrical pressure of the electrical atmosphere of a thunder cloud.
The ancient notion of a thunderbolt, or stony mass, falling at the stroke of light ning, seems to have obtained no small de gree of force from the modern observa tions and researches concerning stones which have fallen from the atmosphere. See STONES, meteoric. From which it ap pears, that other substances as well as wa ter are not unfrequently condensed and precipitated from the air, and exhibit the most astonishing degrees of heat and electricity during their condensation.