improvement of knowledge, and to the liberality with which you communicate what you acquire to the rest of mankind. I hope your philosophers on this voyage will be able to discover more clearly the cause of the Aurora Borealis, and a passage round the North of America.

I suppose care has been taken to make their ships very strong, that they may bear thumping among the ice. My best wishes will attend them for their success and safe return.

Messrs. Banks and Solander are to sail with two ships in about a fortnight for the South. They expect to be out near four years. They present their compliments, and are pleased with the notice you honor them with in your letter to me. Sir John Pringle continues well, and presents his respectful compliments to you. I am, with the most perfect esteem,

Dear Sir, yours, &c.

B. FRANKLIN.

TO JOSEPH PRIESTLEY.

Electrical Experiments.

-

Imperfection of the Abbé Nollet's Electrical Machine. One on an improved Construction sent to M. Le Roy.

DEAR SIR,

London, 4 May, 1772.

I think with you that there cannot be the least occasion for my explaining your method of impregnating water with fixed air to Messrs. Banks and Solander, as they were present, and I suppose are as well acquainted with it as myself; however, I shall readily do it, if they think it necessary. I am glad you intend to improve and publish the process.

You must go half an inch farther with your spark to exceed what I showed here with my Philadelphia machine in 1758, to Lord Charles Cavendish and others, who judged them to be nine inches. My cushion was of buckskin, with a long damp flap, and had a wire from it through the window down to the iron rails in the yard; the conductor of tin four feet long and about four inches diameter. So powerful a machine had then never been seen in England before, as they were pleased to tell me. A machine was made from mine for Mr. Timmer, and was afterwards in the possession of Lord Morton. A more convenient construction I have never since seen, except that of yours. I intend soon to repeat Barletti's experiments, being provided with the requisites, and shall let you know the result.

I should be glad to see the French translation of your book. Can you conveniently lend it to me when you have perused it? I fancy it was translated at the request of Abbé Nollet by a friend and disciple of his; as I know there was one (whose name I have forgotten), that used to translate for him extracts of English electrical books.

The Abbé's machine was a very bad one, requiring three persons to make the smallest experiment, one to turn the great wheel, and one to hold hands on the globe. And the effect after all was but weak. De Lor had a similar one, and invited me to see him exhibit to the Duchess of Rochefoucauld; but, the weather being a little warm, he could perform nothing, scarce obtaining a spark.

This inconvenience must have occasioned his making fewer experiments, and of course his not being so easily convinced. M. Le Roy however got early possession of the truth, and combated for it with Nollet; yet I think the Academy rather favored the latter.

Le Roy will, I suppose, now confute this translator, for I have just seen a letter of his to Mr. Magelhaens, thanking him for sending so excellent an electrical machine to France, (it is one of the plate ones,) which he has improved so as to produce the positive and negative electricities separately or together at the same time. "De façon," says he, "qu'on peut faire toutes les expériences possibles sur l'une ou l'autre de ces deux électricités. Enfin on étoit si eloigné de connoître les phénomènes de ces deux électricités ici, faute de machines commodes de les demontrer, que beaucoup des gens ont été étonnés de voir avec quelle évidence ils établissent la distinction de ces deux électricités," &c. This letter is of the 5th instant. My best wishes attend you and yours. I am ever, with great respect, my dear friend,

You make me very happy by the near prospect of seeing you and Sir John Pringle at Leeds. I shall be entirely at liberty to receive you, and I hope you will contrive to stay as long as possible in this town and neighbourhood. I thank you for the Native of New England.* I had casually seen the same paper, and

* Probably alluding to a piece entitled Toleration in Old England and New England, and signed A NEW ENGLAND MAN. This piece was first printed in "The London Packet," June 3d, 1772. See Vol. II. p. 112. EDITOR.

was particularly struck with it, without having any suspicion of Poor Richard being the author of it. I am obliged to you for your advice with respect to the Dedication, and shall comply with it; but some other alterations, besides what you noted, must be made in it, if it be addressed to Lord Sandwich only.

I am intent upon the prosecution of my experiments on air, and since I wrote to you have observed several remarkable appearances. That very extraordinary kind of air, which Dr. Hales got from Walton pyrites, and which I had despaired of procuring, I get from all the metals I have yet tried, by means of spirit of nitre. It is quite transparent; but a mixture of it and common air is red for a considerable time, in which the whole quantity is greatly reduced in bulk. A mixture of this and fixed air is not turbid. This air alone is reduced above one half by a mixture of iron filings and brimstone standing in it, whereas common air is diminished only about one fifth in the same process.

When I have the pleasure of seeing you, I shall acquaint you with some other remarkable properties of this new kind of air. In the mean time you will do me a very important service by procuring for me, and bringing along with you, a little of highly concentrated marine acid. There is none to be got here; and, using a weaker sort in the solution of gold, I was obliged to apply a considerable degree of heat, the consequence of which was, that, the acid menstruum suddenly boiling, my hands, face, clothes, and the walls of the room have been great sufferers by it, as, I am afraid, I shall be able to show you. A pennyweight of gold, which I had bought for the purpose, was also lost.

As a reward for this damage, I preserved about three ounce measures of air extracted from gold, which I believe was never seen before, and have the prodigious

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.

I

DEAR SIR,

Leeds, 1 July, 1772.

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