The foregoing very sensible and distinct account may afford a good deal of instruction relating to the nature and effects of lightning, and to the construction and use of this instrument for averting the mischiefs of it. Like other new instruments, this appears to have been at first in some respects imperfect; and we find that we are, in this as in others, to expect improvement from experience chiefly: But there seems to be nothing in the account, that should discourage us in the use of it; since at the same time that its imperfections are discovered, the means of removing them are pretty easily to be learnt from the circumstances of the account itself; and its utility upon the whole is manifest.

One intention of the pointed rod, is, to prevent a stroke of lightning. (See pages 126, 162.) But to have a better change of obtaining this end, the points should not be too near to the top of the chimney or highest part of the building to which they are affixed, but should be extended five or six feet above it; otherwise their operation in silently drawing off the fire (from such fragments of cloud as float in the air between the great body of cloud and the earth) will be prevented. For the experiment with the lock of cotton hanging below the electrified prime conductor, shews, that a finger under it, being a blunt body, extends the cotton, drawing its lower part downwards; when a needle with its point presented to the cotton, makes it fly up again to the prime conductor; and that this effect is strongest, when as much of the needle as possible appears above the end of the finger; grows weaker as the needle is shortened between the finger and thumb; and is reduced to nothing when only a short part below the point appears above the finger. Now it seems the points of Mr. Maine’s rod were elevated only (a) six or seven inches above the top of the chimney; which, considering the bulk of the chimney and the house, was too small an elevation. For the great body of matter near them would hinder their being easily brought into a negative state by the repulsive power of the electrised cloud, in which negative state it is that they attract most strongly and copiously the electric fluid from other bodies, and convey it into the earth.

(b) Nothing of the points, &c. could be found. This is a common effect. (See page 163.) Where the quantity of the electric fluid passing is too great for the conductor thro’ which it passes, the metal is either melted, or reduced to smoke and dissipated; but where the conductor is sufficiently large, the fluid passes in it without hurting it. Thus these three wires were destroyed, while the rod to which they were fixed, being of greater substance, remained unhurt; its end only, to which they were joined, being a little melted, some of the melted part of the lower ends of those wires uniting with it, and appearing on it like solder.

(c) (d) (e) As the several parts of the rod were connected only by the ends being bent round into hooks, the contact between hook and hook was much smaller than the rod; therefore the current through the metal being confin’d in those narrow passages, melted part of the metal, as appeared on examining the inside of each hook. Where metal is melted by lightning, some part of it is generally exploded; and these explosions in the joints appear to have been the cause of unhooking them; and, by that violent action, of starting also most of the staples. We learned from hence, that a rod in one continued piece is preferable to one composed of links or parts hooked together.

(f) No part of the chimney was damaged; because the lightning passed in the rod. And this instance agrees with others in shewing, that the second and principal intention of the rods is obtainable, viz. that of conducting the lightning. In all the instances yet known of the lightning’s falling on any house guarded by rods, it has pitched down upon the point of the rod; and has not fallen upon any other part of the house. Had the lightning fallen on this chimney, unfurnished with a rod, it would probably have rent it from top to bottom, as we see, by the effects of the lightning on the points and rod, that its quantity was very great; and we know that many chimneys have been so demolished. But no part of this was damaged, only (f) (g) (h) at the foundation, where it was shattered and several bricks torn out. Here we learn the principal defect in fixing this rod. The lower joint being sunk but three feet into the earth, did not it seems go low enough to come at water, or a large body of earth so moist as to receive readily from its end the quantity it conducted. The electric fluid therefore thus accumulated near the lower end of the rod, quitted it at the surface of the earth, dividing in search of other passages. Part of it tore up the surface in furrows, and made holes in it: Part entered the bricks of the foundation, which being near the earth are generally moist, and, in exploding that moisture, shattered them. (See page 415.) Part went through or under the foundation, and got under the hearth, blowing up great part of the bricks (m) (s), and producing the other effects (o) (p) (q) (r). The iron dogs, loggerhead and iron pot were not hurt, being of sufficient substance, and they probably protected the cat. The copper tea kettle being thin, suffered some damage. Perhaps, tho’ found on a sound part of the hearth, it might at the time of the stroke have stood on the part blown up, which will account both for the bruising and melting.

That it ran down the inside of the chimney (k) I apprehend must be a mistake. Had it done so, I imagine it would have brought something more than soot with it; it would probably have ripp’d off the pargetting, and brought down fragments of plaister and bricks. The shake, from the explosion on the rod, was sufficient to shake down a good deal of loose soot. Lightning does not usually enter houses by the doors, windows, or chimneys, as open passages, in the manner that air enters them: Its nature is, to be attracted by substances, that are conductors of electricity; it penetrates and passes in them, and, if they are not good conductors, as are neither wood, brick, stone nor plaister, it is apt to rend them in its passage. It would not easily pass thro’ the air from a cloud to a building, were it not for the aid afforded it in its passage by intervening fragments of clouds below the main body, or by the falling rain.

It is said that the house was filled with its flash (l). Expressions like this are common in accounts of the effects of lightning, from which we are apt to understand that the lightning filled the house. Our language indeed seems to want a word to express the light of lightning as distinct from the lightning itself. When a tree on a hill is struck by it, the lightning of that stroke exists only in a narrow vein between the cloud and the tree, but its light fills a vast space many miles round; and people at the greatest distance from it are apt to say, “the lightning came into our rooms through our windows.” As it is in itself extreamly bright, it cannot, when so near as to strike a house, fail illuminating highly every room in it through the windows; and this I suppose to have been the case at Mr. Maine’s; and that, except in and near the hearth, from the causes abovementioned, it was not in any other part of the house; the flash meaning no more than the light of the lightning. It is for want of considering this difference, that people suppose there is a kind of lightning not attended with thunder. In fact there is probably a loud explosion accompanying every flash of lightning, and at the same instant; but as sound travels slower than light, we often hear the sound some seconds of time after having seen the light; and as sound does not travel so far as light, we sometimes see the light at a distance too great to hear the sound.

(n) The breaking some pieces of china in the beaufet, may nevertheless seem to indicate that the lightning was there: But as there is no mention of its having hurt any part of the beaufet, or of the walls of the house, I should rather ascribe that effect to the concussion of the air, or shake of the house by the explosion.

Thus, to me it appears, that the house and its inhabitants were saved by the rod, though the rod itself was unjointed by the stroke; and that, if it had been made of one piece, and sunk deeper in the earth, or had entered the earth at a greater distance from the foundation, the mentioned small damages (except the melting of the points) would not have happened.