Abbildungen der Seite


Giving an Account of a Work published by him,

entitled Filosofia Frankliniana.


Forli, 15 August, 1772. Sir, In submitting to you my little work, entitled Filosofia Frankliniana sopra le Punte Preservatrici del Fulmine, &c., I place it in the hands of a philosopher, known to the public as one of the most distinguished, whose happy inventions have so greatly advanced the progress of Natural Philosophy. Your great mind, truly English, and your enlightened views, have been directed to the subject of protecting houses and other edifices from lightning.

Availing myself of your ideas, I have thought of extending these preservatives to vessels and to magazines of powder. I propose every thing as derived from you, and as such I acknowledge it. I am very desirous of knowing your opinion of this little work. I shall profit by your suggestions. It will give me great pleasure, Sir, if you have time, and will have the goodness to inform me whether in America, or in England, these defences against lightning have ever been used for vessels; or, whether you, Mr. Watson, or others have invented such preservatives. Pray excuse my inquisitiveness, and if you will favor me with an answer, you can leave it with Mr. Berlendis, Venetian Minister at London. I am, with great respect, Sir,

Your most obedient, &c.


of the Society of Jesus.



London, 8 December, 1772.

When the glasses are ranged on the horizontal spindle, or, to make use of your expression, enfilés, and each one is definitely fixed in its place, the whole of the largest glass appears, at the extremity to the left; the following one, nearly enclosed in the preceding one, shows only about an inch of its border, which advances so much further than the edge of the larger glass; and so, in succession, each glass exceeds the one containing it, leaving by this placement an uncovered border on which the fingers may be applied. The glasses do not touch one another, but they are so near as not to admit a finger to pass between them; so that the interior border is not susceptible of being rubbed.

The finger is to be applied flat on the borders of the largest glasses, and on the borders of the smaller; but in part on the borders, and in part on the edges, of the glasses of an intermediate size. Nothing but experience can instruct with respect to this manutation, (fingering,) because the different-sized glasses require to be touched differently, some nearer the edge, and others farther from it. A few hours' exercise will teach this.

B. F.

* See a description of the Armonica above, pp. 245–250; and also plate X.

Some Directions for drawing out the Tones from the

Glasses of the Armonica.

Before you sit down to play, the fingers should be well washed with soap and water, and the soap well rinsed off.

The glasses must be always kept perfectly clean from the least greasiness; therefore suffer nobody to touch them with unwashed hands; for even the common slight natural greasiness of the skin rubbed on them will prevent their sounding for a long time.

You must be provided with a bottle of rain water, (spring water is generally too hard and produces a harsh tone,) and a middling sponge in a little slopbowl, in which you must keep so much of the water' that the sponge may be always very wet.

In a teacup keep also ready some fine scraped chalk, free from grit, to be used on occasion.

The fingers when you begin to play should not only be wet on the surface, but the skin a little soaked, which is readily done by pressing them hard a few times in the sponge.

The first thing after setting the glasses in motion is to pass the sponge slowly along from the biggest glass to the smallest, suffering it to rest on each glass during at least one revolution of the glasses, whereby they will all be made moderately wet. If too much water is left on them, they will not sound so readily.

If the instrument is near a window, let the window be shut or the curtain drawn, as wind or sunshine on the glasses dries them too fast.

When these particulars are all attended to, and the directions observed, the tone comes forth finely with the slightest pressure of the fingers imaginable, and




you swell it at pleasure by adding a little more pressure, no instrument affording more shades, if one may so speak, of the Forte Piano.

One wetting with the sponge will serve for a piece of music twice as long as Handel's Water-piece, unless the air be uncommonly drying.

But a number of thin slices of sponge, placed side by side, and their ends held fast between two stripes of wood, like rulers, of a length equal to the glasses, and placed so that the loose ends of the sponges may touch the glasses behind, and by that means keep them constantly wet, is very convenient where one proposes to play a long time.

a long time. The sponges being properly wetted will supply the glasses sufficiently a whole evening, and touching the glasses lightly do not in the least hurt the sound.

The powder of chalk is useful two ways.

Fingers, after much playing, sometimes begin to draw out a tone less smooth and soft, and you feel as well as hear a small degree of sharpness. In this case, if you dip the ends of your wet fingers in the chalk, so as to take up a little, and rub the same well on the skin, it will immediately recover the smoothness of tone desired. And, if the glasses have been sullied by handling, or the fingers not being just washed have some little greasiness on them, so that the sounds cannot easily be produced, chalk so used will clean both glasses and fingers, and the sounds will come out to your wish.

A little practice will make all this familiar; and you will also find by trials what part of the fingers most readily produces the sound from particular glasses, and whether they require to be touched on the edge chiefly, or a little more on the side; as different glasses require a different touch, some pretty full on the flat side of the brim, to bring out the best tone, others more on the edge, and some of the largest may need the touch of two fingers at once.

Of the Stilling of Waves by Means of Oil. Extracted

from sundry Letters between Benjamin Franklin, L. L. D., F. R. S., William Brownrigg, M. D., F. R. S., and the Reverend Mr. Farish.


Extract of a Letter from Dr. Brownrigg to Dr. Franklin,

dated Ormathwaite, 27 January, 1773.

By the enclosed from an old friend, a worthy clergyman at Carlisle, whose great learning and extensive knowledge in most sciences would have more distinguished him, had he been placed in a more conspicuous point of view, you will find, that he had heard of your experiment on Derwent Lake, and has thrown together what he could collect on that subject; to which I have subjoined one experiment from the relation of another gentleman.

Extract of a Letter from the Reverend Mr. Farish, to

Dr. Brownrigg. “I some time ago met with Mr. Dun, who surprised me with an account of an experiment you had tried upon the Derwent Water, in company with Sir John Pringle and Dr. Franklin. According to his representation, the water, which had been in great agitation before, was instantly calmed upon pouring in only a very small quantity of oil, and that to so great a distance round the boat as seemed incredible. I have

« ZurückWeiter »