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with respect and affection, as does Dr. Huck and all

that knew you.

I am ever, with the sincerest esteem, dear Sir,
Your faithful and most obedient servant,


Experiments on Alkaline Air.


Calne, 14 October, 1773.

I hope you received my letter, in which I gave you some account of my discovery of an alkaline air, though I have not had the pleasure of hearing from you since. I am still busy in examining its properties and affinities, some of which are curious enough. The most remarkable observation I have made is, of the manner in which it affects alum put into it. This substance absorbs it very fast, and then comes out perfectly white, and altogether unlike what it was; but I have not yet examined it any further.

I have also found, that this alkaline air is slightly inflammable. This is not observed without attention, for a candle dipped into it goes out several times before there is much appearance of its inflammability. This, however, agrees with the opinion of chemists, that volatile alkali contains phlogiston.

As you have not written to me, I hope you are planning an excursion to Calne with Sir John Pringle, or some of our friends. This would make me very happy. I am, with great respect, &c.


Six weeks after the date of the above letter, that is, on the 30th of November, 1773, Dr. Priestley received from the Royal Society the


Communicating a Philosophical Paper.


Lichfield, 24 January, 1774.

I have enclosed a medico-philosophical paper, which I should take it as a favor if you will communicate to

Copley Medal, in honor of his discoveries of various properties of air. For the Discourse of the President of the Royal Society on the occasion, see SIR JOHN PRINGLE'S Six Discourses, p. 1.

Before the Council of the Society had decided on bestowing the medal, Dr Franklin was requested to examine Dr. Priestley's book and report his opinion. To a nobleman, a member of the Council, (whose name is not written on the draft of the letter that remains,) he replied as follows. "My Lord; In obedience to your Lordship's cominands, I have looked over that part of Dr. Priestley's work, that contains an account of the experiments made by him. I find there is a great number of them, mostly quite new, and some I think very curious and important, well deserving for that reason, and for the great pains and expense he has been at in making them, the honor of the Society's medal. I am, however, so engaged at present, that I could not possibly prepare any thing of the kind, fit to be laid before the Council on Thursday, and hope your Lordship will be so good as to excuse me. I do not see that his account of them can well be abridged; and, as the book has been long published, and probably is in the hands of all those of the Society, who, from their acquaintance with the subject, are the best judges of the merit of such experiments, I apprehend that any other account is hardly necessary. With the greatest respect," &c.. - EDITOR.

* An acquaintance of long standing, and a correspondence on philosophical subjects, seem to have subsisted between Dr. Franklin and Dr. Darwin, but none of Franklin's letters to Darwin have come within my researches. The only record of their intercourse, contained in Miss Seward's "Memoirs of Dr. Darwin," is the following anecdote. "When he wrote to Dr. Franklin, complimenting him on having united philosophy to modern science, he directed his letter merely thus, Dr. Franklin, America,' and said he felt inclined to make a still more flattering superscription; Dr. Franklin, the World.' His letter reached the sage, who first disarmed the lightning of its fatal power, for the answer to it arrived, and was shown in the Darwinian circles; in which had been questioned the likelihood of Dr. Franklin ever receiving a letter of such general superscription, as the whole western empire." SEWARD'S Memoirs of Dr Darwin, p. 152. — EDITOR.

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the Royal Society, if you think it worthy a place in their volume; otherwise, I must desire you to return it to the writer. I have another very curious paper containing experiments on the colors seen in the closed eye, after having gazed some time on luminous objects, which is not quite transcribed, but which I will also

send to you, if you think it is likely to be acceptable

to the Society at this time, but will otherwise let it lie by me another year.

I hope you continue to enjoy your health, and that I shall some time again have the pleasure of seeing you at Staffordshire. I am, dear Sir,

Your affectionate friend,



Answers to Questions on Philosophical Subjects.


London, 20 March, 1774.

I am ashamed that my late continued embarras in public affairs should have so long prevented my answering the letter you honored me with, of the 2d of De

cember last.

I transmitted your queries to our Society at Philadelphia, where they will be well considered, and full answers will be sent to you. On my return thither, which I am now preparing for, I shall take care, if not done, to urge the doing it as soon as possible

In the mean time, I can inform you, as to question first, that, though there is in Pennsylvania abundance of limestone and marble, no flint has yet been found there by the English; yet it is supposed, that flint is to be met with in some part of the country, since heads

of arrows made of it by the ancient inhabitants are sometimes found in ploughing the fields. Thus, small sea shells are found intermixed with the substance of rock-stone in some of our highest mountains, and such I think as are not now to be met with on our coasts. Several skeletons, supposed by their tusks to be of elephants, have been found near the Ohio, an account of which may be found in the English Philosophical Transactions.

As to question second, observations have been made in America of the variation of the needle, and, as well as I can remember, it is found to differ a degree in about twenty years.

As to question third; the height of the barometer, by many years' observation, is said to vary between 28.59 and 30.78. The conjectures from these changes are still uncertain.

As to question fourth; the negroes, who are free, live among the white people, but are generally improvident and poor. I think they are not deficient in natural understanding, but they have not the advantages of education. They make good musicians.

As to question fifth; I do not know that any marks of volcanoes, any lava, or pomice-stone, have been met with in North America. Pit-coal is found in many places, and very good, but little used, there being plenty of wood.

These answers are very short. I hope to procure you such as shall be more full and satisfactory.

With great respect, I have the honor to be, Sir, &c. B. FRANKLIN


English Translation of Beccaria's Book. - -Experiment to show that Electricity does not pass through a perfect Vacuum.


London, 20 March, 1774.

I have received several of your favors lately, relating to the edition of your book in English, which I have put into the hands of the translator, who will observe your directions. The work is now in the press, and goes on pretty fast. I am much obliged by your kind assistance in procuring the impressions from the plates. They are not yet arrived here; but the money, which I find by a note from you to Dr. Priestley amounts to one hundred and forty-three livres of Piedmont, will be paid by the bookseller, Mr. Nourse, in my absence, to any person you may order to receive it.

Mr. Walsh, the same ingenious member of our Society who went to France to make experiments on the Torpedo, has lately hit on a new discovery in electricity, which surprises us a little. You know that finding air, made rarer by the pump or by heat, gave less obstruction to the passage of electricity, than when in its denser state, we were apt to think a perfect vacuum would give it no resistance at all. But he, having by boiling the mercury made a perfect vacuum in a long bent Torricellian tube, has found that vacuum absolutely to resist the passage of the electric fluid during two or three days, or till some quantity of air, the smallest imaginable, is admitted into it. This, if verified by future experiments, may afford some new light to the doctrine


*The remainder of the letter is lost. - EDITOR.

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