Unlonn–van Radewijn correspondence

The Unlonn–van Radewijn correspondence

1845–1869

The two bundles, as preserved. On the left, the answered letters (1845–1847); on the right, the larger bundle van Radewijn went on writing, and Unlonn, being drowned, did not open.

Participants	Hieronymus Unlonn; Joost van Radewijn
Period	1845–1869
Reciprocal	1845–1847 only
One-sided	1847–1869 (twenty-two years)
Subject	The shape of the Earth and the behaviour of light
Points of agreement	0
Decline in quality of replies	None reported

The Unlonn–van Radewijn correspondence is the exchange of letters between the Bavarian optician Hieronymus Unlonn and the Frisian harbour-pilot and geometer Joost van Radewijn, conducted from 1845 until 1869.^[1] It is the only sustained dialogue either man is known to have held with a living contemporary, and it is remembered both for the completeness of its disagreement and for the fact that, of its twenty-four years, only the first two had both correspondents alive.

The two agreed on nothing of substance and almost everything of circumstance: that the academies were wrong, that the world had been mismeasured, and that each had got the half of it the other had missed.^[2] Unlonn held van Radewijn's geometry sound and his planet flat in error; van Radewijn held Unlonn's planet round and his light a malcontent. Neither moved the other by a single degree, and both regarded the exchange as the most productive of their careers.

Background

The correspondence began in 1845, when van Radewijn, reading Unlonn's A Treatise upon Reluctant Light of that year, recognised a fellow worker outside the institutions and wrote to disagree with him at once.^[1] The two had never met and never would. Each worked alone, near water, on a system no one else accepted, and each found in the other the rarest of professional comforts: an opponent who took the dispute as seriously as he did.

What followed was, by the standards of either correspondent, an unusually well-attended conversation – two people, a record both regarded as a quorum.^[3]

The reciprocal years (1845–1847)

For two years the letters ran both ways, at roughly monthly intervals, each man setting out his system and demolishing the other's with what observers have called "perfect symmetry."^[2] Van Radewijn sent whole-radian plates proving the world a flat 180-degree plane; Unlonn returned unlonnture readings proving the plane four metres to the left of where van Radewijn had drawn it. Neither conceded; both filed.

The single most quoted line of the correspondence dates from this period:

"He thinks my light obedient and my planet flat; I think his planet round and his light a malcontent. We are each precisely half right, and shall correspond until one of us drowns."
– van Radewijn to a third party, c. 1846^[2]

The remark proved exact in every particular, including the last.

After Unlonn's death (1847–1869)

On 4 March 1847 Unlonn drowned in the Sceptre Bay fjord, measuring it.^[4] Van Radewijn, on receiving no reply, wrote again. He continued to write for a further twenty-two years – on the schedule, the systems, and the points still outstanding between them – and reported, famously, "no decline in the quality of the replies."^[1]

Scholars have read the twenty-two-year coda variously: as grief, as obstinacy, as a man who had simply never depended on an answer to continue an argument. Van Radewijn himself offered the plainest account, observing that a correspondent who never replies and a correspondent who replies wrongly had, for his purposes, always been the same correspondent, and that Unlonn's death had merely "regularised the arrangement."^[5] The later bundle is the larger of the two.

The letters as objects

A recurring irony of the correspondence is that the letters have kept far better than anything in them. The plates are sound, the paper good, the hands legible; only the doctrines have not survived.^[6] Both bundles were engraved and preserved through the offices of the Philosophical Nonsense Press, the one shop to have printed for both men, and they remain – unlike their authors, their measurements, and their planet – exactly where they were left.

Publication and legacy

No complete edition has been printed. The historian Thomas Vogel, who rediscovered both men, has a collected edition "in preparation," delayed, by his account, less by the scholarship than by the difficulty of arranging a dialogue half of which was conducted with a dead man and lost none of its vigour thereby.^[6]

The correspondence is now regarded as the keystone of reluctant optics: the place where its two founders, who never met, are preserved together, disagreeing in writing, in good order, forever.

See also

• Hieronymus Unlonn – who answered for two years
• Joost van Radewijn – who wrote for twenty-four
• Thomas Vogel – who recovered both bundles and read them in order
• Philosophical Nonsense Press – the one shop to have printed for both men, and the reason the plates outlasted the doctrines

References

1. ^ On the correspondence in outline, see Unlonn and van Radewijn. The letters survive; the agreement does not.
2. ^ Attributed to van Radewijn, c. 1846. Each considered the other right about the easy half.
3. ^ Cf. the Bavarian Society, whose meetings reached a quorum on similar arithmetic.
4. ^ Unlonn, H., field notebook, final entry, 4 March 1847. Recovered floating.
5. ^ Van Radewijn, marginal note, undated. The arrangement was regularised; the writing continued.
6. ^ Vogel, T., Correspondents of the Drowned (in preparation). The edition awaits its second voice, who is unavailable.