# Revisited: The Langrenus cryptogram

Belgian scholar Michael Florent van Langren (1598-1675) proposed a naval navigation method that didn’t work. A second method he developed might be described a cryptogram that has never been solved.

In October 2015, I blogged about Belgian scholar Michael Florent van Langren (1598-1675), also known as Langrenus. Van Langren’s claim to fame is a method by which the crew of a ship at sea could determine the longitude of their current position. Whoever has read the book Longitude by Dava Sobel knows how important this issue once was. While it was quite easy to find out the latitude (based on the position of the sun), it used to be impossible to determine the longitude accurately. This often led to disastrous navigation errors.

### A non-working method

For this reason, scholars in the seafaring nations for centuries desperately searched for a suitable longitude determination method. Governments raised high rewards for solving this problem. It was not until the middle of the 18th century that a practicable method was finally developed. It required a clock accurate to the second, as it was first possible to build at that time.

Van Langren published his proposal for the determination of longitude in 1644. It was based on a precise observation of the lunar surface. The details are described in a paper by Michael Friendly, Pedro Valero-Mora and Joaquíin Ibáñez Ulargui. The following diagram played a role in van Langren’s method:

Source: Friendly, Valero-Mora, and Ibáñez Ulargui

Toledo, Spain, was the place the prime meridian went through in the geographic coordinate system used at the time. The other points marked on the horizontal axis refer to locations on the moon.

If van Langren’s method had worked, he would have gone down in history. However, it proved impracticable, and so it only enriched the long list of longitude failures.

### The Langrenus cryptogram

According to the aforementioned paper, van Langren later developed a second method for determining the longitude. He informed the Spanish royal court about it in an encrypted letter (I call it “Langrenus cryptogram”). This letter has survived, but the cleartext is unknown.

Source: Friendly, Valero-Mora, and Ibáñez Ulargui

Here is a transcription of the Langrenus cryptogram (also provided by Friendly, Valero-Mora, and Ibáñez Ulargui):

```ImIeV9  ap3Apa  Ihrr5e  tlSmeIf9  5lesEortEr  5e  eadnu9c  Rtl9e9T  omgupea  Nſnnd  cAlveMa
dfneagL  p9rIir5  rEant  tdTeo9Im  nc5T9t  noqCtuN  veroQn  nnmEef  alarRl  9kIe  raIman
Me4tn  eqtIu  u4xV  eu  ulriqDa  ſuVne  etſelId  ſe5tſ  couAu  9ſ9Vldu  lir5te  Tce4o  vEe7oſnE
i5uameg  Ebſe  lodRa  9ebtſl  Sa95u  rVcmai  AenprIt  a9dL3do9  9nRt  e3enqQe  cun5ef
Etſot  dEr  5emus  Oeacdſae  5ucſoMe  e9lrrI9  acnuoEd  umr92  L5d9a5  eI9cnai  dnneNt  t4pAIeai
gPrmrO  e5e  VnſzbmF  oaenſeS5  uſlOnt  teoDe  p9noIl  l9lo  Enen  trEge59  cut  To  9uned
V9neq  ItduLau  Deum  NamDe  nEerEmſ9  9LmdVl  eR99mEe  e5nOu  rdTd9  oOedu
I9oVa5  nqnp  ntEaE  eerlVrt  lLrT9  5etoſ  Y9ntl  Sfrnae  eG9a6  rſaiIau  uulAnoTtp  9qVe  ruIcſeT
t9pOu  erE9  leLſln  Ecedo  EſrNn  eMeſu  3Nove  Ar9ſ  VmdtS  qcVeueEd  oVn9nufu  R9fenPe
utrTl  5eAten  Aftca  qTe9u  prSa  a5trOl  rle5ef  hRſ95  eDluſ  Iert5  eoVa  ſ9qc  lS  u  elalet
eſ9Oſd  qtuuef  eſ9pero  tmuaaru  mumeuen  yſtdm  aeeuNr  9tlne  eſnmſt  pTdaſ  9n3t  taMe
qnſutu  euDalnſa  depesE  rſeedtm9  l9tVe5e  ſrſaeu  H9uia  aſnſet  tReſrc  ſe  eomſ9p  ſtAle  v9du
Qdc95  3dLloe  eu5ale  uea4Rrfe  ſ9l5na4  dAme  5nnr  neoeſR  nrtcaro  oe7uſOn  uuoer9r  pſtc
tEn9e  rnresEa  aoplna  afrſa  lSe9  Eecrſoae  nTfſ4l  teoolLt  9atlq  elnr  eeuſlCn  elune  e3frLo  97mneb
9tE9r  teaena  aduNue  ſ4tſ9Ve  ytm  ccpaNe  ſnled9  lCln  ladXedr  ſS9eſ  tſe5u  uepuIſ  p9todNo
re9tnl  etlpLe  eaeſ  rqeEurua  aeE9alau  qCnmu  te5Snſ  lom9t  Ce5em  gRoeenr  dPl9ea
dNq9  9nTſeos  nyMed  4ru9al  ec9uoeE  Inuold  ue  uurdeD.```

After my first blog post in 2015, my readers published a number of interesting comments. A reader named Schorsch posted some interesting background information about van Langren and his work on the longitude problem.

However, nobody came up with an idea on how the Langrenus cryptogram could be broken. The frequency analysis (created with Christian Baumann’s Multi-Dec) …

… is consistent with the Dutch language. So, we might be dealing with a transposition cipher. However, it is far from clear what the numbers and the capital letter mean. Was an additional encryption step applied?

Can a reader find out more? After over 350 years, it’s time to solve this mystery.

Further reading: Tony Gaffney’s starlight steganogram

## Kommentare (5)

1. #1 Magnus Ekhall
Borensberg
4. Dezember 2019

Since the letter was sent to the Spanish court, and the figure has the text “Grados de la Longitud”, perhaps the encrypted letter is in Spanish instead of Dutch?

2. #2 Norbert
4. Dezember 2019

refer to locations on the moon.

This has already been clarified in 2015 by schorsch.

The points on the right-hand side of the graph refer to the longitude of Rome (“ROMA”) as proposed by several authors. By which Langren demonstrates how unreliable the methods of his time were.

3. #3 x3Ray
4. Dezember 2019

I have no idea, but somehow the “words” remind me of Latin, which could’ve been the lingua franca at that time.

4. #4 Tony
4. Dezember 2019

When I looked at this many years ago I came to the conclusion it should be read backwards because I became convinced this section represented his name –

9tE9r 97mneb e3frLo elune eeuflCn
autor Miguel Florencio Van Legran Valencis

but I couldn’t solve it.

5. #5 Matthew Brown
4. Dezember 2019

I’m leaning towards it being a transposition cipher, the frequencies seem like a good match for Spanish.

The long s symbol is normally only used at the beginning or middle of a word but appears at the end of some words in the ciphertext, which may suggest they have been moved from their original positon?
https://en.wikipedia.org/wiki/Long_s

The text the cipher comes from has the convention of using all upper case for names and places, which may explain the unusually high number of upper case letters in the ciphertext.