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an unpublished letter from henry oldenburg to johann heinrich rahn

an unpublished letter from henry oldenburg to johann heinrich rahn

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Downloaded <strong>from</strong><br />

rsnr.royalsocietypublishing.org on December 6, 2012<br />

258 Noel Malcolm<br />

subject, but that, nevertheless, he has not yet published it, I thought I should mention it <strong>to</strong> you,<br />

in order <strong>to</strong> find out your thoughts about it.<br />

So far as optics are concerned, we are delighted that you have completed a treatise on<br />

optics, dioptrics, <strong>an</strong>d ca<strong>to</strong>ptrics, <strong>to</strong>gether with <strong>an</strong> appendix on practical dioptrics, in which you<br />

show the way (<strong>an</strong>d perhaps the measure), <strong>an</strong>d the necessary <strong>to</strong>ols, for grinding <strong>an</strong>d polishing<br />

[lenses]. 41 We hope that copies of it will soon be delivered <strong>to</strong> us. No doubt you already know<br />

M<strong>an</strong>zini’s Dioptrica, 42 <strong>an</strong>d the Novum problematum opticorum centuria by Eschinardi, 43 published<br />

in Italy; we have recently learned that <strong>an</strong>other work has been published there, the<br />

Dioptrica by de Gottignies, a pupil of Grégoire de Saint-Vincent, <strong>to</strong>gether with a treatise on telescopes<br />

<strong>an</strong>d microscopes. 44 There is also the Synopsis optica of Honoré Fabri, which discusses<br />

the ocular lens consisting of two half-lenses, <strong>to</strong>uching at the centres of their convex sides, <strong>an</strong>d<br />

each having the pl<strong>an</strong>e side facing outwards: this is like the one invented by the most distinguished<br />

Eustachio Divino, but Fabri claims that he was the first <strong>to</strong> demonstrate it. 45 In addition, there is<br />

the eleg<strong>an</strong>t Dioptrique of Father Cherubin, recently published in Fr<strong>an</strong>ce, 46 <strong>to</strong> which Regnauld of<br />

Lyon pays the following tribute: he says that he admires the beauty of this publication, that he<br />

greatly prefers the author’s theory which is set out in it, <strong>an</strong>d that he thinks the Republic of Letters<br />

will be indebted <strong>to</strong> him. 47 Here in London Barrow’s Lectiones dioptricae have been published,<br />

<strong>an</strong>d are much admired. 48 In Denmark Erasmus Bartholinus published a dissertation De chrystallo<br />

isl<strong>an</strong>dico dis-diaclastico, in which he painstakingly explores m<strong>an</strong>y things, <strong>an</strong>d learnedly explains<br />

them. 49 You c<strong>an</strong>not be unaware of the work which your countrym<strong>an</strong> the most learned Joh<strong>an</strong>nes<br />

Ott recently published in Heidelberg, entitled Cogitationes physico-mech<strong>an</strong>icae de natura visionis.<br />

50<br />

Otherwise, the Itali<strong>an</strong>s have published Rossetti’s physico-mathematical treatise; 51<br />

Benedet<strong>to</strong> Castelli’s works, collected in one volume; 52 Bali<strong>an</strong>i’s posthumous minor works; 53<br />

Borelli’s Motiones naturales in gravitate dependentes; 54 Mont<strong>an</strong>ari’s experiments on the rising<br />

of liquids in tubes, <strong>an</strong>d on the glass bubbles which, when their extremities are broken, shatter in<strong>to</strong><br />

extremely small parts; 55 <strong>an</strong>d Mengoli’s works on music. 56 In Fr<strong>an</strong>ce they have published<br />

Blondel’s De resistentia corporum ellipticorum; 57 Milliet de Chales’s edition of Euclid; 58<br />

Mou<strong>to</strong>n’s De mensura diametri solis et lunae; 59 An<strong>to</strong>ine de la Loubère’s polemical Appendices,<br />

against Maign<strong>an</strong>; 60 <strong>an</strong>d Honoré Fabri’s commentaries on Archimedes. 61 And, indeed, in Engl<strong>an</strong>d<br />

we have Dr Wallis’s De motu et libra; his De calculo centri gravitatis; his De regulis motis, vi<br />

percussionis, et hydrostatica; 62 James Gregory’s Exercitationes geometriae; 63 <strong>an</strong>d Nicolaus<br />

Merca<strong>to</strong>r’s Logarithmotechnia. 64 Jeremy Horrox’s work on astronomy, edited by Dr Wallis, is<br />

currently in the press. 65<br />

Since you so c<strong>an</strong>didly offer <strong>to</strong> send details of the optical instruments which you have prepared,<br />

we welcome your generosity, <strong>an</strong>d with the greatest pleasure we promise in return <strong>to</strong> send<br />

you whatever things may serve <strong>to</strong> express our gratitude. The reason why our friend Hooke was<br />

able <strong>to</strong> observe on such a large scale the things he has illustrated in his Micrographia is explained<br />

by him in the preface <strong>to</strong> his book: <strong>an</strong>yone skilled in the English l<strong>an</strong>guage will easily be able <strong>to</strong><br />

tr<strong>an</strong>slate it for you. 66 I should [not] prolong this <strong>letter</strong>—for the excessive prolixity of which I beg<br />

your pardon. Farewell, distinguished Sir, <strong>an</strong>d look kindly on this most devoted admirer of your<br />

teachings <strong>an</strong>d your virtue.<br />

London, 10 June 1671<br />

RAHN’S LETTER TO PELL<br />

Oldenburg did not receive <strong>an</strong>y reply <strong>from</strong> Rahn. An expl<strong>an</strong>ation—at least, <strong>an</strong> ostensible<br />

expl<strong>an</strong>ation—of this fact was supplied four years later, when Rahn at long last wrote<br />

directly <strong>to</strong> his old mathematics tu<strong>to</strong>r, John Pell. The text of his <strong>letter</strong> (figure 2) is as<br />

follows.<br />

À studioso quodam, Algebram, non amplius meam sed multis nominibus tuam, mihi ex munificentia<br />

tua tr<strong>an</strong>smissam accepi, unde colligo, <strong>to</strong>t <strong>an</strong>norum decursu, memoriam mei, adhuc apud te

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