Oeuvres complètes. Tome V. Correspondance 1664-1665

N^o 1288.
R. Hooke à [R. Boyle].
23 décembre 1664¹⁾.

La lettre a été publiée dans ‘Boyle's Works, Vol. V.’

Decembre 13. 1664.

Most honoured Sir,

I am not only ashamed, that I have not sooner given you an account of what I promised in my last²⁾, but much more, that I am able as yet to say so little to the

1) Cette lettre n'a été expédiée que le 25 décembre 1664. Consultez la Lettre N^o. 1289.

2) Cette lettre de Hooke à Boyle était du 24 novembre 1664 (V. st.).

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purpose; for though, when I last writ, I was promised, both by Master Faithorne³⁾



and Master Thompson⁴⁾, that I should have those things which they had in their hands, finished within three or four days; and though I have often called upon them, and urged them all I could, I have not been able to get them done. I have lately observed many circumstances in the height of the mercurial cylinder, which do very much cross my former observations; for at this very time the quicksilver is as high as I have a long time observed it, and I don't remember, that it has been higher: it has risen a little for these four or five days, and has continued so, notwithstanding the variety of winds, and the multitude of rain, that has lately fallen; and, I think, it rises a little yet, but it is but little.

I have taken notice also of two or three other very odd particulars lately in it, which have crossed several other observations. The experiments we are now most busy about⁵⁾, are concerning the adjustening of the length of pendulums, thereby to settle a common standard for length; of which kind, Monsieur Zulichem has sent over⁶⁾ some very pretty theories; but upon very careful trial with several accurate and large pendulums, made with balls of lignum vitae⁷⁾, some of which balls are six inches over, others no bigger than the head of a pin, or a small shot, and sus-

3) Faithorne était graveur, au service de la Société Royale.

4) Thompson était graveur à Londres.

5) Dans les ‘Proceedings’ de la Royal Society on lit, au sujet des premières expériences faites dans la séance du 7 décembre 1664 (V. st.), ce qui suit:
The experiment for the verifying of Monsieur Huygens's rule concerning the universal measure was made twice, there being taken a very small bullet with a line of the lenght of 15 3/10 inches: and two wooden balls, one of three, the other of six inches; which being adjusted with the former line, it was found in the first trial that the line of the ball of three inches diameter was 13½ inches long: which added to the semi-diameter of the ball made the length of the vibration from the point of suspension to be fifteen inches, and the line of the ball of six inches diameter was twelve inches long, which added to the semi-diameter of the ball, made the whole length to be fifteen inches. In the second trial it was as before, except that the pendulum with the ball of three inches was adjusted to 13 11/20, to make it vibrate equally with the other two.
This being calculated and compared with Monsieur Huygens's rule was found to approach very near to it.

6) Consultez la Lettre N^o. 1274.

7) Lignum vitae était alors le nom du bois de gaïac.

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pended by a very curious hair, which seems as likely a way as any to find out to what point of the globular body, hung at the end of a string, the length of such a pendulum is to be reckoned. Monsieur Zulichem says, it is ⅖ parts of a third proportional below the center of the ball c, the first of which proportionals are, ab + bc (that is, ac) and bc; namely, ab + bc, bc ∷ bc; bc bc/ab + bc, which we will suppose ce; ⅖ of which taken below the centre gives d the point, to which the length of the pendulum ad is to be measured from a, the point of suspension. Sure it is, that this point is below c, the center of the body; but whether at d, I cannot positively yet affirm.

The plate for your book⁸⁾ was graven before I received your last of Monsieur Evelyn's. I have only taken notice of seven instruments, which you in those sheets I looked on have described; and those I so put into one small plate, that they will fold out of the book, when there is occasion. This last of Monsieur Evelyn⁹⁾ I have given a small draught of also to the engraver, who is not an Englishman, but one that I find a very good workman, and very punctual to his word; which was the reason I did not employ Master Faithorne, as you directed, he having so very often and often disappointed my expectation. I have since my last made an anatomy of a dog, and hope, that I have made a considerable new discovery; but this being the first time I have seen it, at least taken notice of it, I cannot, till further trial, positively affirm any thing, which, as soon as ever I am assured of it, you shall thereof receive an account from,

Sir

Your most faithful and most humble servant R. Hooke.

I hope, Sir, you will pardon this hasty scribble, for it was very near eleven a clock this night, before I could get from some company, met¹⁰⁾ about the business of Sir J. Cutler.

8) L'ouvrage cité dans la Lettre N^o. 1289, note 6.

9) Probablement pour son ouvrage:
Kalendarium Hortense. London. Printed by Jo. Martyn and Jac. Allerstay, Printers to the Royal Society, and are to be sold at their shop at the Bell in St. Paul's Church Yard. mdclxiv. in-folio.

10) Dans la séance de la Société Royale du 7 décembre 1664 (V. st.), sir W. Petty, Dr. Wilkins et W. Graunt furent chargés de rédiger le programme des cours de R. Hooke et de le montrer à sir J. Cutler, le fondateur de ce ‘lecturership’, pour en savoir son opinion.