TO DAVID HUME.*

On the Method of securing Houses from the Effects of Lightning.

DEAR SIR,

London, 24 January, 1762.

In compliance with my Lord Marischal's request, communicated to me by you, when I last had the pleasure of seeing you, I now send you what at present appears to me to be the shortest and simplest method of securing buildings, &c., from the mischiefs of lightning. Prepare a steel rod five or six feet long, half an inch thick at its biggest end, and tapering to a sharp point; which point should be gilt to prevent its rusting. Let the big end of the rod have a strong eye or ring of half an inch diameter: Fix this rod upright to the chimney or highest part of the house, by means of staples, so as it may be kept steady. Let the pointed end be upwards, and rise three or four feet above the chimney or building that the rod is fixed to. Drive into the ground an iron rod of about an inch diameter, and ten or twelve feet long, that has also an eye or ring in its upper end. It is best that the rod should be at some distance from the foundation of the building, not nearer than ten feet, if your ground will allow so much. Then take as much length of iron rod of about half an inch diameter, as will reach from the eye in the rod above, to that in the rod below; and fasten it securely to those rods, by passing its ends through the rings, and bending those ends till they likewise form rings.

*First printed in the third volume of a work entitled, "Essays and Observations, Physical and Literary; read before the Philosophical Society in Edinburgh, and published by them." Mr. Hume was a member of that Society. The volume containing the above letter was published in the year 1771. EDITOR.

VOL. VI

16

This length of rod may either be in one or several pieces. If in several, let the ends of the pieces be also well hooked to each other. Then close and cover every joint with lead, which is easily done, by making a small bag of strong paper round the joint, tying it close below, and then pouring in the melted lead; it being of use in these junctures, that there should be a considerable quantity of metalline contact between piece and piece. For, if they were only hooked together, and so touched each other but in points, the lightning, in passing through them, might melt and break them where they join. The lead will also prevent the weakening of the joints by rust. To prevent the shaking of this rod by the wind, you may secure it by a few staples to the building, till it comes down within ten feet of the ground, and thence carry it off to your ground rod; near to which should be planted a post, to support the iron conductor above the heads of people walking under it.

If the building be large and long, as an hundred feet or upwards, it may not be amiss to erect a pointed rod at each end, and form a communication by an iron rod between them. If there be a well near the house, so that you can by such a rod form a communication from your top rod to the water, it is rather better to do so than to use the ground rod above mentioned. It may also be proper to paint the iron, to render it more durable by preserving it from rust.

A building thus guarded, will not be damaged by lightning, nor any person or thing therein killed, hurt, or set on fire. For, either the explosion will be prevented by the operation of the point; or, if not prevented, then the whole quantity of lightning exploded near the house, whether passing from the cloud to the earth, or from the earth to the cloud, will be conveyed

in the rods. And, though the iron be crooked round the corner of the building, or make ever so many turns between the upper and lower rod, the lightning will follow it, and be guided by it, without affecting the building. I omit the philosophical reasons and experiments on which this practice is founded; for they are many, and would make a book. Besides they are already known to most of the learned throughout Europe. In the American British colonies, many houses have been, since the year 1752, guarded by these principles. Three facts have only come to my knowledge of the effects of lightning on such houses.*

If I have not been explicit enough in my directions, I shall, on the least intimation, endeavour to supply the defect.

I am, &c.

B. FRANKLIN.

FROM DAVID HUME TO B. FRANKLIN.

Remarks on the Mode of constructing Lightning-Rods. Compliment to Dr. Franklin as a Philosopher and a Man of Letters.

DEAR SIR,

Edinburgh, 10 May, 1762.

I have a great many thanks to give you for your goodness in remembering my request, and for the exact description, which you sent me of your method of preserving houses from thunder. I communicated it to

*The statement of the three facts is here omitted, as they are those relating to the houses of Mr. West in Philadelphia, and of Mr. Raven and Mr. Maine in South Carolina, which are described in Volume V. pp. 375, 395, 396. EDITOR.

our Philosophical Society, as you gave me permission ; and they desire me to tell you, that they claim it as their own, and intend to enrich with it the first collection, which they may publish. The established rule of our Society is, that, after a paper is read to them, it is delivered by them to some member, who is obliged, in a subsequent meeting, to read some paper of remarks upon it.

It was communicated to our friend, Mr. Russel; who is not very expeditious in finishing any undertaking; and he did not read his remarks, till the last week, which is the reason, why I have been so late in acknowledging your favor. Mr. Russel's remarks, besides the just praises of your invention, contained only two proposals for improving it. One was, that in houses, where the rain-water is carried off the roof by a lead pipe, this metallic body might be employed as a conductor to the electric fire, and save the expense of a new apparatus. Another was, that the wire might be carried down to the foundation of the house, and be thence conveyed below ground to the requisite distance, which would better secure it against accidents. I thought it proper to convey to you these two ideas of so ingenious a man, that you might adopt them, if they appear to you well founded.

I am very sorry, that you intend soon to leave our hemisphere. America has sent us many good things, gold, silver, sugar, tobacco, indigo, &c.; but you are the first philosopher, and indeed the first great man of letters for whom we are beholden to her. It is our own fault, that we have not kept him; whence it appears, that we do not agree with Solomon, that wisdom is above gold; for we take care never to send back an ounce of the latter, which we once lay our fingers upon.

I saw yesterday our friend Sir Alexander Dick, who desired me to present his compliments to you. We are all very unwilling to think of your settling in America, and that there is some chance for our never seeing you again; but no one regrets it more than does, Dear Sir,

Your most affectionate humble servant,

DAVID HUME.

TO JOHN BAPTIST BECCARIA.

Describing a new Musical Instrument composed of Glasses.

London, 13 July, 1762.

REVEREND SIR,

I once promised myself the pleasure of seeing you at Turin; but, as that is not now likely to happen, being just about returning to my native country, America, I sit down to take leave of you (among others of my European friends that I cannot see) by writing.

I thank you for the honorable mention you have so frequently made of me in your letters to Mr. Collinson and others, for the generous defence you undertook and executed with so much success, of my electrical opinions; and for the valuable present you have made me of your new work, from which I have received great information and pleasure. I wish I could in return entertain you with any thing new of mine on that subject; but I have not lately pursued it. Nor do I know of any one here, that is at present much engaged in it.

Perhaps, however, it may be agreeable to you, as you live in a musical country, to have an account of