ANSWER TO M. DUBOURG'S QUERIES RESPECTING THE

ARMONICA.*

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

VOL. VI.

45

DD*

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. 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.

READ AT THE ROYAL SOCIETY, JUNE 2d, 1774.

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

since had the same accounts from others, but I suspect all of a little exaggeration. Pliny mentions this property of oil as known particularly to the divers, who made use of it in his days, in order to have a more steady light at the bottom.* The sailors, I have been told, have observed something of the same kind in our days, that the water is always remarkably smoother, in the wake of a ship that has been newly tallowed, than it is in one that is foul. Mr. Pennant also mentions an observation of the like nature made by the seal-catchers in Scotland. (Brit. Zool. Vol. IV., Article SEAL.) When these animals are devouring a very oily fish, which they always do under water, the waves above are observed to be remarkably smooth, and by this mark the fishermen know where to look for them. Old Pliny does not usually meet with all the credit I am inclined to think he deserves. I shall be glad to have an authentic account of the Keswick experiment; and, if it comes up to the representations that have been made of it, I shall not much hesitate to believe the old gentleman in another more wonderful phenomenon he relates, of stilling a tempest only by throwing up a little vinegar into the air."

Sir Gilfred Lawson, who served long in the army at Gibraltar, assures me, that the fishermen in that place are accustomed to pour a little oil on the sea, in order to still its motion, that they may be enabled to see the oysters lying at its bottom; which are there very large, and which they take up with a proper instrument. This Sir Gilfred had often seen there performed, and said the same was practised on other parts of the Spanish coast.-Note by Dr. Brownrigg.