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. EDITOR. pp. 375, 395, 396. ·

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.

REVEREND SIR,

London, 13 July, 1762.

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

the new instrument lately added here to the great number that charming science was before possessed of. As it is an instrument that seems peculiarly adapted to Italian music, especially that of the soft and plaintive kind, I will endeavour to give you such a description of it, and of the manner of constructing it, that you or any of your friends may be enabled to imitate it, if you incline so to do, without being at the expense and trouble of the many experiments I have made in endeavouring to bring it to its present perfection.

You have doubtless heard the sweet tone that is drawn from a drinking-glass by passing a wet finger round its brim. One Mr. Puckeridge, a gentleman from Ireland, was the first who thought of playing tunes, formed of these tones. He collected a number of glasses of different sizes, fixed them near each other on a table, and tuned them by putting into them water more or less, as each note required. The tones were brought out by passing his fingers round their brims. He was unfortunately burned here, with his instrument, in a fire which consumed the house he lived in. Mr. E. Delaval, a most ingenious member of our Royal Society, made one in imitation of it, with a better choice and form of glasses, which was the first I saw or heard. Being charmed by the sweetness of its tones, and the music he produced from it, I wished only to see the glasses disposed in a more convenient form, and brought together in a narrower compass, so as to admit of a greater number of tones, and all within reach of hand to a person sitting before the instrument, which I accomplished, after various intermediate trials and less commodious forms, both of glasses and construction, in the following manner.

The glasses are blown as near as possible in the form of hemispheres, having each an open neck or

socket in the middle. (See Plate X. Figure 1.) The thickness of the glass near the brim about a tenth of an inch, or hardly quite so much, but thicker as it comes nearer the neck, which in the largest glasses is about an inch deep, and an inch and half wide within, these dimensions lessening, as the glasses themselves diminish in size, except that the neck of the smallest ought not to be shorter than half an inch. The largest glass is nine inches diameter, and the smallest three inches. Between these two are twenty-three different sizes, differing from each other a quarter of an inch in diameter. To make a single instrument there should be at least six glasses blown of each size; and out of this number one may probably pick thirty-seven glasses (which are sufficient for three octaves with all the semitones) that will be each either the note one wants or a little sharper than that note, and all fitting so well into each other as to taper pretty regularly from the largest to the smallest. It is true there are not thirty-seven sizes, but it often happens that two of the same size differ a note or half note in tone, by reason of a difference in thickness, and these may be placed one in the other without sensibly hurting the regularity of the taper form.

The glasses being chosen, and every one marked with a diamond the note you intend it for, they are to be tuned by diminishing the thickness of those that are too sharp. This is done by grinding them round from the neck towards the brim, the breadth of one or two inches, as may be required; often trying the glass by a well-tuned harpsichord, comparing the tone drawn from the glass by your finger, with the note you want, as sounded by that string of the harpsichord. When you come nearer the matter, be careful to wipe the glass clean and dry before each trial, because the tone