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hearth was torn up (s). My wife's sister, two children, and a negro wench were all who happened to be in the house at the time; the first and one child sat within five feet of the chimney, and were so stunned, that they never saw the lightning nor heard the explosion; the wench, with the other child in her arms, sitting at a greater distance, was sensible of both; though every one was so stunned that they did not recover for some time; however, it pleased God that no farther mischief ensued. The kitchen, at ninety feet distance, was fujl of negroes, who were all sensible of the shock; and some of them tell me, that they felt the rod about a minute after, when it was so hot that they could not bear it in hand."
Remarks by Benjamin Franklin.
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 313, 356.) But, to have a better chance 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 aflixed, 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 shows, 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 electrized 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, Sfc. could be found. This is a common effect. (See page 358.) Where the quantity of the electric fluid passing is too great for the conductor through 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. • .
(cj (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 confined 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 learn from hence, that a rod in one continued piece is preferable to one composed of links or parts hooked together.
(/) No part of the chimney was damaged; because the lightning passed in the rod. And this instance agrees with others in showing, 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 - * v;
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 393.) Part went through or under the foundation, and got under the hearth, blowing up great part of the bricks (m) ($), and producing the other effects (0) (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, though 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 ripped off the pargeting, and brought down fragments of plaster 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 plaster, it is apt to rend them in its passage. It would not easily pass through the air from a cloud to a building, were it not for the aid afforded in its passage by
Vol. v. 51 HH*
intervening fragments of clouds below the main body, or by the falling rain.
It is said, that the house was filled with its flash (/). 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 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 extremely 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 above mentioned, 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 buffet, may nevertheless seem to indicate that the lightning was there; but, as there is no mention of its havjng hurt any part of the buffet, 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.