summit of the roof, and taper off gradually till it ends in a sharp point; and, the better to preserve this point, the last six inches should be of brass, because it is less liable to become blunted by rust. If the rod cannot well be made entirely of a single piece, the different pieces composing it should be strongly screwed together, or into one another very closely, with a thin plate of lead between the joints, in order to render the junction or continuation of the metal more perfect.

After all the electrical experiments that I have made in reference to this subject, and all the examples that have come to my knowledge of the effects of lightning on these conductors, it seems to me that (provided they are good and perfect, carried down till water or very moist ground is reached) they are equally safe, whether placed directly against the wall, and secured by staples driven into it, or whether supported by a pole or staff planted in the ground, at some distance from the wall. The former is the better rod, as the rod can be bent to avoid the windows or doors, which are situated directly below the summit of the roof. Yet, as certain apprehensions may be more effectually set at rest by supporting the rods in the other manner, I should make no objection to this, provided that they can be suitably placed, without interfering with any passage, and that they are so firmly fixed that the wind cannot, by causing them to vibrate, interrupt the communication of iron or lead between the side of the rod and the lead that covers the ridge.

3. As I am informed that the roofs of the other four buildings are to be reconstructed after the model

of that of which I have just been speaking, the same method may be followed with regard to them, when they are finished in this manner. But if it be asked how they may be rendered secure in the meantime, I would advise that (as their roofs are now of a different form, being hip-roofs with four corners, and the joining at their corners, as well as their ridgepieces, having a coping of lead, which extends to the gutters) the passages which it is proposed to carry down till water is reached, be bored or dug immediately, and that that part of each conductor which is to be carried up from the water as high as the gutters, be fixed in them. From the top of this conductor I would carry out two arms of iron to the corners of the gutters, where the leaden coping of the corners of the roof should be united to the ends of these bars; and at the junction of these corners with the ridge-piece, I would carry up rods to the height of ten feet, pointed as directed above; which, when a new roof is made, could be used for the upper part of a straight conductor. I am, Sir,

Your most obedient humble servant,

B. FRANKLIN. P. S. For that part of the conductor which is to be carried under ground, leaden pipes should be used, as less liable to rust.'

1 In consequence of this letter the Ordnance Department directed that the advice of the writer should be followed in some respects; but that they might be still better authorized to proceed with regard to other points, these gentlemen were desirous to obtain the sanction of the Royal Society, and therefore requested their opinion. The Royal Society appointed Messrs. Cavendish, Watson, Franklin, Wilson, and Robertson, a committee to examine the subject, and report thereon.DUBOURG.

CCCCXLII

FROM JOSEPH PRIESTLEY TO B. FRANKLIN

LEEDS, 3 June, 1772.

DEAR SIR:-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 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

I 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 3, 1772. See supra, page

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 meantime 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

VOL. V.-22.

use to me in a future edition of my work, I think to purchase it. In the meantime 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.

CCCCXLIII

TO MR. MASERES

CRAVEN STREET, 17 June, 1772. SIR: I thank you for the pamphlets proposing to establish Life Annuities in Parishes, &c. I think it an excellent one. In compliance with your wish, pages 25, 26, I send it back with a few marginal notes (perhaps of no great importance) made in reading it, requesting it may be returned to me.

In page 118 of Dr. Price's book on Annuities, 2d edition, you will find mention made of an institution in Holland. He had that information from me. Those houses are handsome, neat buildings, with very comfortable apartments. Some form the sides of a square, with grass-plots and gravel walks, flowers, &c., and some have little separate gardens be