satisfaction of finding, that it has the very same properties with that which is produced from copper. If I had studied Poor Richard in time, I should not have indulged myself in these expenses; but bad habits are not easily corrected. If, however, the passion be not kept up by considerable success, frugality and an attention to a growing family will, at length, get the better of experimenting, and then I shall write nothing but Politics or Divinity, to furnish the Bishop of Llandaff with more quotations for his future invectives against the Dissenters.

The French translation of my "History of Electricity" I borrowed of Mr. Walsh; but, as it will be of some use to me in a future edition of my work, I think to purchase it. In the mean time Mr. Walsh will have no objection to your having it for what time you please, and I can give it to you when you are here.

I am surprised that the French electricians should not have been able to provide themselves with better machines. I am confident that plates will never answer so well as globes or cylinders. I am, with my respectful compliments to Sir John Pringle,

Dear Sir, yours sincerely,

JOSEPH PRIESTLEY.

P. S. I wish you could bring Dr. Price with you.

FROM JOSEPH PRIESTLEY TO B. FRANKLIN.

Curious Experiments on Air, and Discoveries of various Properties.

DEAR SIR,

Leeds, 1 July, 1772.

I presume that by this time you are arrived in London, and I am willing to take the first opportunity of

informing you, that I have never been so busy, or so successful in making experiments, as since I had the pleasure of seeing you at Leeds.

I have fully satisfied myself, that air, rendered in the highest degree noxious by breathing, is restored by sprigs of mint growing in it. You will probably remember the flourishing state in which you saw one of my plants. I put a mouse in the air, in which it was growing, on the Saturday after you went away, which was seven days after it was put in, and it continued in it five minutes without showing any sign of uneasiness, and was taken out quite strong and vigorous, when a mouse died after being not two seconds in a part of the same original quantity of air, which had stood in the same exposure without a plant in it. The same mouse, also, that lived so well in the restored air, was barely recoverable after being not more than one second in the other. I have also had another instance of a mouse living fourteen minutes without being at all hurt in little more than two ounce measures of another quantity of noxious air, in which a plant had grown.

I have completely ascertained the restoration of air, in which tallow or wax candles, spirit of wine, or brimstone matches, have burned out by the same means.

The nitrous air, which I showed you, I found to be an admirable test of air that is fit for breathing. It makes this air red and turbid, but no other that I have tried. I took air, in which a mouse had putrefied, which was in the highest degree noxious and fetid, and also a quantity of fixed air. The nitrous air, admitted to each of these kinds of air separately, made no sensible alteration in them; but, when they were mixed (which I discovered to make a wholesome air), the nitrous air male the mixture turbid and diminished the bulk of it, as in common air, though not in the same

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 ja 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 sealing. wax, 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.

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.