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TO T. HOPKINSON.

Paris, January 3, 1786.

Dear Sir,

I wrote you last on the 25th of September. Since that I have received yours of October the 25th, enclosing a duplicate of the last invented tongue for the harpsichord. The letter enclosing another of them, and accompanied by newspapers, which you mention in that of October the 25th, has never come to hand. I will embrace the first opportunity of sending you the crayons. Perhaps they may come with this, which I think to deliver to Mr. Bingham, who leaves us on Saturday, for London. If, on consulting him, I find the conveyance from London uncertain, you shall receive them by a Mr. Barrett, who goes from hence for New York, next month. You have not authorized me to try to avail you of the new tongue. Indeed, the ill success of my endeavors with the last does not promise much with this. However, I shall try. Houdon only stopped a moment, to deliver me your letter, so that I have not yet had an opportunity of asking his opinion of the improvement. I am glad you are pleased with his work. He is among the foremost, or, perhaps, the foremost artist in the world.

Turning to your Encyclopédie, Arts et Metiers, tome 3, part 1, page 393, you will find mentioned an instrument, invented by a Monsieur Renaudin, for determining the true time of the musical movements, largo, adagio, &c. I went to see it. He showed me his first invention; the price of the machine was twenty-five guineas: then his second, which he had been able to make for about half that sum. Both of these had a mainspring and a balance-wheel, for their mover and regulator. The strokes are made by a small hammer. He then showed me his last, which is moved by a weight and regulated by a pendulum, and which cost only-two guineas and a half. It presents, in front, a dial-plate like that of a clock, on which are arranged, in a circle, the words largo, adagio, andante, allegro, presto. The circle is moreover divided into fifty-two equal degrees. Largo is at 1, adagio at 11, andante at 22, allegro at 36, and presto at 46. Turning the index to any one of these, the pendulum (which is a string, with a ball hanging to it) shortens or lengthens, so that one of its vibrations gives you a crochet for that movement. This instrument has been examined by the academy of music here, who were so well satisfied of its utility, that they have ordered all music which shall be printed here, in future, to have the movements numbered in correspondence with this plexi-chronometer. I need not tell you that the numbers between two movements, as between 22 and 36, give the quicker or slower degrees of the movements, such as the quick andante, or moderate allegro. The instrument is useful, but still it may be greatly simplified. I got him to make me one, and having fixed a pendulum vibrating seconds, I tried by that the vibrations of his pendulum, according to the several movements. I find the pendulum regulated to

Every one, therefore, may make a chronometer adapted to his instrument.

For a harpsichord, the following occurs to me:

In the wall of your chamber, over the instrument, drive five little brads, as, 1, 2, 3, 4, 5, in the following manner. Take a string with a bob to it, of such length, as, that hung on No. 1, it shall vibrate fifty-two times in a minute. Then proceed by trial to drive No. 2, at such a distance, that drawing the loop of the string to that, the part remaining between 1 and the bob, shall vibrate sixty times in a minute. Fix the third for seventy vibrations, &c.; the cord always hanging over No. 1, as the centre of vibration. A person playing on the violin may fix this on his music-stand. A pendulum thrown into vibration will continue in motion long enough to give you the time of your piece. I have been thus particular, on the supposition that you would fix one of these simple things for yourself.

You have heard often of the metal called platina, to be found only in South America. It is insusceptible of rust, as gold and silver are, none of the acids affecting it, excepting the aqua regia. It also admits of as perfect a polish as the metal hitherto used for the specula of telescopes. These two properties had suggested to the Spaniards the substitution of it for that use. But the mines being closed up by the government, it is difficult to get the metal. The experiment has been lately tried here by the Abbe Rochon (whom I formerly mentioned to Mr. Rittenhouse, as having discovered that lenses of certain natural crystals have two different and uncombined magnifying powers), and he thinks the polish as high as that of the metal heretofore used, and that it will never be injured by the air, a touch of the finger, &c. I examined it in a dull day, which did not admit a fair judgment of the strength of its reflection.

Good qualities are sometimes misfortunes. I will prove it from your own experience. You are punctual; and almost the only one of my correspondents on whom I can firmly rely, for the execution of commissions which combine a little trouble with more attention. I am very sorry however that I have three commissions to charge you with, which will give you more than a little trouble. Two of them are for Monsieur de Buffon. Many, many years ago, Cadwallader Golden wrote a very small pamphlet on the subjects of attraction and impulsion, a copy of which he sent to Monsieur de Buffon. He was so charmed with it, that he put it into the hands of a friend to translate, who lost it. It has ever since weighed on his mind, and he has made repeated trials to have it found in England. But in vain. He applied to me. I am in hopes, if you will write a line to the booksellers of Philadelphia to rummage their shops, that some of them may find it. Or, perhaps, some of the careful old people of Pennsylvania or New Jersey may have preserved a copy. In the King’s cabinet of Natural History, of which Monsieur de Buffon has the superintendence, I observed that they had neither our grouse nor our pheasant. These, I know, may be bought in the market of Philadelphia, on any day while they are in season. Pray buy the male and female of each, and employ some apothecary’s boys to prepare them, and pack them. Methods may be seen in the preliminary discourse to the first volume of Birds, in the Encyclopédie, or in the Natural History of Buffon, where he describes the King’s cabinet. And this done, you will be so good as to send them to me. The third commission is more distant. It is to precure me two or three hundred paccan nuts from the western country. I expect they can always be got at Pittsburgh and am in hopes, that by yourself or your friends, some attentive person there may be engaged to send them to you. They should come as fresh as possible, and come best, I believe, in a box of sand. Of this, Barham could best advise you. I imagine vessels are always coming from Philadelphia to France. If there be a choice of ports, Havre would be the best. I must beg you to direct them to the care of the American consul or agent at the port, to be sent by the Diligence or Fourgon. A thousand apologies would not suffice for this trouble, if I meant to pay you in apologies only. But I sincerely ask, and will punctually execute, the appointment of your chargé des affaires in Europe generally. From the smallest to the highest commission, I will execute with zeal and punctually, in buying, or doing any thing you wish, on this side the water. And you may judge from the preceding specimen, that I shall not be behind hand in the trouble I shall impose on you. Make a note of all the expenses attending my commissions, and favor me with it every now and then, and I will replace them. My daughter is well, and retains an affectionate remembrance of her ancient patroness, your mother, as well as of your lady and family. She joins me in wishing to them, and to Mr. and Mrs. Rittenhouse and family, every happiness. Accept, yourself, assurances of the esteem with which I am, Dear Sir,

your friend and servant,

Th: Jefferson.

P.S. What is become of the Lunarium for the King?