an unpublished letter from henry oldenburg to johann heinrich rahn

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252 Noel Malcolm
I wish you could … learne from Zurich, concerning Johan Heinrich Rahn, lately Landvogt der
Graffschaft Kyburg, whether he be yet alive, whether he be now at Zurich, what titles or offices
he hath now. You gave me his booke in November 1660. I suppose you know that it is turned into
English, and that 15 sheets of it are printed. Some mention should be made of him, if we can get
sufficient information concerning him. 10
From the absence of such details about Rahn in the printed volume, it would appear
that Haak’s attempts to carry out this task met with no success during the following two
years. But in 1671 he did make contact with Rahn (who had in fact returned to Zurich in
1664). On 17 May 1671 Rahn wrote what was evidently a reply to Haak’s enquiries, giving
news of his own scientific work and asking for details of new mathematical publications
in England. On receiving this letter, Haak seems to have passed it on to Oldenburg;
his motives for doing so would probably have included both a desire to stimulate contacts
between The Royal Society and foreign scientists, and the feeling that Oldenburg
was particularly well placed to provide news of recent publications. Oldenburg, in turn,
passed the letter to John Collins, who was playing an increasingly active role as his
adviser on mathematical matters. All that survives of Rahn’s letter to Haak (to which
Oldenburg’s letter to Rahn is in effect a reply) is the following extract made by Collins,
which was later copied out (together with other associated items from Collins’s papers)
by David Sinclair and sent to Collins’s correspondent in Scotland, James Gregory.
RAHN’S LETTER TO HAAK
Ex literis D ni Johannis Henrici Rahn, Secretioris consilij Tigurini ad Theodorum Haak, redditis
17 o Maij 1671
Ego praeterito jam aliquo tempore, insistens manuductioni D ni Pellij (cui quicquid in Algebra
scio, unice acceptum fero) problemata Diophanti Alexandrini ad Speciosam reduxi et constitui.
nuper etiam tractatum absolvi de Optica, Catoptrica et Dioptrica cum annexa dioptrica
practica exhibente modum et instrumenta necessaria limandis et poliendis vitris, et haec quidem
non ex mera ideâ, sed ex ipsa praxi, et usu sese mihi obtulere cum subinde curiositate delecter,
non tantum tubos majores et minores et microscopia construendi, sed insuper etiam rationem
invenerim prope partem interiorem, seu circuitum Rotae medium sectiones Hyperbolicas affirmandi,
quarum beneficio objecta admodum perspicua redduntur, et campus visorius egregie
dilatatur, Si tibi adlubescit videre Iconismum horum Instrumentorum, aut ejusmodi vitra objectiva
et ocularia dabo operam ut tibi transmittantur, interim libenter viderem Hookij vestri
Micrographiam utinam latine loquentem.
Contigit mihi non ita pridem observare (au Journal des scavants) Figuram ingenti
admodum formâ minima repraesentantem, 11 sed non constat mihi proportio istius Microscopij,
quod vitris constet, quis sit uniuscujusq[ue] vitri diameter; et quantum vitra ab invicem distent.
Nos enim nondum eo usq[ue] progressi sumus, nec cogitata nostra ultra tertium vitrum
extendimus.
Si quid aliud etiam vobiscum in Mathematicis prodijt, notatu dignum, ne graveris quaeso
illud impertiri nobis ad omnia officia paratissimis. 12
Translation
From the letter of Mr Johann Heinrich Rahn, Secretary-Councillor of Zurich, to Theodore Haak,
written on 17 May 1671