degree. A mouse put into this mixture lived five minutes without uneasiness, when, if it had been put into either of them separately a few minutes before, it would have died in a few seconds.

Air, that has passed through hot charcoal, has many, perhaps all the properties of air that has been diminished by other processes. It extinguishes flame, kills animals, and is not diminished or made turbid by a mixture of nitrous air.

But the observation, that pleases me more than any I ever made, is the diminution of air by the crystallization (I believe) of quicksilver and the nitrous acid. This effect both precedes and follows the generation of nitrous air from the same mixture. This I suspect to be the case with other crystallizations.

I have observed many other things, which I have not room to mention at present.

I am, with great respect, dear Sir,

Yours sincerely,

JOSEPH PRIESTLEY.

FROM JOHN WALSH TO B. FRANKLIN.*

Experiments for ascertaining the Electrical Properties of the Torpedo.

DEAR SIR,

La Rochelle, 12 July, 1772.

It is with particular satisfaction I make to you my first communication, that the effect of the Torpedo ap

Mr. Walsh was the first person, who ascertained from a series of experiments, that the shock communicated by the species of ray-fish called the Torpedo, is the same as that derived from the Leyden jar when charged with electricity. He had received directions from Dr.

pears to be absolutely electrical, by forming its circuit through the same conductors with electricity, for instance, metals and water; and by being intercepted by the same non-conductors, for instance, glass and sealing-wax. I will not at present trouble you with a detail of our experiments, especially as we are daily advancing in them, but only observe, that, having discovered the back and breast of the animal (I speak in particular of that assemblage of pliant cylinders described by Lorenzini, running perpendicularly from the skin of the back to that of the breast,) to be in different states of electricity, we have been able to convey his shocks, though they were very small, through a circuit of four persons all feeling them; likewise through a considerable length of wire held by two insulated persons, one touching his lower surface and the other his upper.

When the wire was exchanged for glass or sealingwax, no effect could be perceived. When resumed, the two persons were again sensible of the shock. These experiments have been varied and repeated times without number, by which the choice of conductors is beyond a doubt determined to be the same in the Torpedo as in the Leyden phial. The sensations they occasion, likewise, in the human frame are precisely similar. There is not an engourdissement or fourmillement of the Torpedo, that we do not exactly imitate with the phial by means of Mr. Lane's elec

trometer.

We have not yet perceived any spark or noise to

Franklin, as to the mode of conducting his experiments. (See Vol. V. pp. 412, 413.) Mr. Walsh's discoveries were deemed of sufficient importance to give him a claim to the Copley Medal, which was conferred on him by the Royal Society, November 30th, 1774. See SIR JOHN PRINGLE'S Six Discourses, p. 45. — Editor,

VOL. VI.

DD

accompany the shock, nor the pith balls to be ever affected. Indeed all our trials have been on very feeble subjects, whose shock was seldom sensible beyond the touching finger. I remember but one in at least two hundred, that I myself must have taken, to have extended above the elbow. Perhaps L'Isle de Ré, which we are about to visit, may furnish us with Torpedos, fresher taken and of more vigor, by which a farther insight into these matters may be obtained. Our experiments have been chiefly in the air, where the animal was more open to our examination than in water. It is a singularity, that the Torpedo when insulated should be able to give us, insulated likewise, thirty, forty, or fifty successive shocks from nearly the same part, and these with very little diminution in their strength; and indeed they were all minute. Each effort to give a shock is conveniently accompanied with a suppression of his eyes, by which even his attempts to give it to non-conductors could be ascertained. The animal, with respect to the rest of his body, is in a great degree motionless, but not wholly so.

You will please to acquaint Dr. Bancroft of our having verified his prediction concerning the Torpedo, and make any other communications of this matter you may judge proper. Here, I shall be glad to excite as far as I am able both electricians and naturalists to push their inquiries concerning this extraordinary animal, while the summer affords them the opportunity.

I am, with the truest sentiments of esteem and regard, dear Sir, &c. JOHN WALSH.

FROM JOHN BAPTIST TODERINI TO B. FRANKLIN.

Giving an Account of a Work published by him, entitled "Filosofia Frankliniana."

TRANSLATION.

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.

if

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, 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.

JOHN BAPTIST TODERINI, of the Society of Jesus.

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.