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In November 2007, the following letter from Mr. George Huxtable was forwarded to me from Mary Root, editor of the Surveyors Historical Society publication, Backsights:

Dear Mary Root,

How kind that was of you to send me those papers, and with a copy of Backsights. What a lively magazine! You must be really proud of your work in creating it. Isn't it interesting the way that the Internet has worked, in that a Dutch hydrographer friend became aware of your piece on levels, which was highly relevant to my enquiry, and helped me to make contact with you.

I don't remember if I told you about the instrument I am investigating with a Danish friend. It's a surveying circle, just for measuring angles in a horizontal plane, no elevations. It was probably usable in the vertical plane as well, with a gooseneck adapter, to fit it to the staff, but that hasn't survived.

It has a telescope with a crosshair, which doesn't "transit". The novel thing about it is that it is, I think, the earliest existing "repeating" instrument, and it has an adjusting screw and pointer which are arranged as a crude micrometer. Such micrometer adjustment wasn't new, but I think it's the earliest to be found on a surveying instrument rather than an astronomical instrument. It was designed, and very likely constructed, by the German astronomer Tobias Mayer, in 1759, for one of his students--a Dane, Carsten Niebuhr, who was being sent off on a scientific expedition to Arab lands, sponsored by the Danish King.

The expedition itself was a tragic fiasco. The scientists quarreled and argued, then succumbed to disease, and in the end the only one left alive was the trusty surveyor of the party. He followed instructions by returning overland from the Persian Gulf to Denmark. What dedication! His instruments, carried across thousands of desert miles on donkey, horse, camel, and backpack survived intact!

Yours,

George

So began a personal adventure that continues to this day. Who was this Carsten Niebuhr chap?

This we know: Born March 17, 1733, he was a farmer in the moist marshlands of coastal northern Germany, a fellow first learning alphabets and mathematics at 22 years of age, a student fortunate enough to study astronomy with Tobias Mayer, a surveyor whose charts of Egypt, the Red Sea, Yemen, the Persian Gulf, and interior Iraq were the standards for over 200 years. Niebuhr's eye for copying various inscriptions led to the later ability to comprehend once incomprehensible ancient scribblings.

A Long, Strange Excursion
Niebuhr, accompanied by four prominent scholars, embarked from Copenhagen, Denmark in January 1761. The expedition included a philologist, a botanist, a physician and an artist as well as the surveyor. A Swedish manservant (a former soldier) shadowed the lads. Their destination was Arabia Felix (literally translated: Happy Arabia). Their mission was to gather various forms of knowledge that would validate, clarify and magnify aspects of the Bible and Christian beliefs.

Over the next five years they traveled first by skirting Iceland, then passing through the Straits of Gibraltar. Visits to Marseilles, Malta, Smyrna, Constantinople and the Isle of Rhodes all preceded a year spent in Egypt--a year spent mapping, botanizing, herbalating, purchasing ancient literature, studying dress and customs, sociology, government, language, and economies in this strange land of Copts, Mohammedans, Jews and Christians. This was the time of the last vestiges of eastern influence on world trade prior to the coming dominance of the western world.

A long, strange trip--on water leaving Suez, and overland through what is now Saudi Arabia--took the group finally to Arabia Felix (present-day Yemen). There were pleasant times and terrifying times. Malaria, a disease unknown to Europeans of the time, struck each member of the group. Their studies and travel plans were constantly interrupted by fever, ague and colds. They all suffered individually in various ways. Two of them never left that "happy land".

From there, an English ship took the remaining four to Bombay, India. On the way, two more perished and were laid to rest in the Indian Ocean. The last (save the surveyor) passed on in Bombay. The malaria Niebuhr contracted never left his body. This stargazer, now alone, who was responsible for all of the research and data gathered to date, departed for Europe. Leaving India, Niebuhr first spent a great deal of time studying and mapping the ruins of Persepolis in Iran. His route then took him through the cities of today's nightly news: Basra, Baghdad and Mosul. On a side trip the lone traveler visited Jerusalem and Damascus, then Bucharest, Warsaw, Dresden and Hanover, to finally journey through the marshlands of his youth (pausing to determine longitude and latitude there) before closing out the traverse in Copenhagen, November 1767.

Examining the Evidence
My minor adventure of 2010 has been to determine the quality of Niebuhr's traverse. Initially speaking, Niebuhr and his team did a marvelous job documenting, mapping and comprehending the Middle East of the middle 18th century. Research material is scarce in America. For English-only speakers, little has been translated. Niebuhr himself published many of his colleagues' papers and journals, none of which I am aware are translated. Edited portions of Niebuhr's own journal are available in three volumes. The first two have been translated into English. The third was published by his son many years after Carsten's death, but no translation is available. Available online is an 1836 translation of a small biography by Niebuhr's son that contains an appendix penned by one of the original planners of the expedition. A popular and common source is Arabia Felix by Thorkild Hansen published in 1962. It reads as a novel of fantasy, but appears to be well researched, having an extensive bibliography. Overall, it is a marvelous read.

Translation also plays a role in understanding Niebuhr's trek. Hansen quotes occurrences, the only source of which could be Niebuhr's journal. My translated versions of the journals contain nothing near the detail that Hansen quotes. I have corresponded with an individual from Denmark who tells me that the English translations of Niebuhr's journals omit any reference to anything technical. I am told there is an immense amount of surveying data not available to the English-speaking world. I have tried to relay only items of the voyage that I believe to be true and verifiable no matter how astounding or fantastic they seem.

Hansen's book reads more like a sensational novel, full of conflict and intrigue. Personalities clash and egos are harmed. Regarding women, some evocative passages are included. A counter story is woven throughout in which one of the party, smarting from slights, conspires to poison the entire group with arsenic. The linguist did indeed purchase enough arsenic in Constantinople to kill "a couple of regiments". Later, in the Suez, the same linguists' spirit is entirely broken in a pitiful melodramatic scene staged in Hansen's words.

When Niebuhr was chosen for the Danish expedition--fully funded by the King--the young Carsten insisted he learn astronomy and advanced mathematics under Tobias Mayer. Mayer had been perfecting a method to determine longitude that didn't require a chronometer. The method he developed became known as the principle of lunar distances. Having already submitted his tables of lunar distances to the Board of Longitude, Mayer seized the opportunity to have his rough-edged student validate the method on this journey to the East. Mayer, who passed away at a young age of 36, received posthumously a portion of the English Board of Longitude prize for his lunar method. Nevil Maskelyne used the tables on his 1761 journey to St. Helena to observe the Transit of Venus. Portions of Mayer's work were included in the British Nautical Almanac and Astronomical Ephemeris in 1766, which included data for 1767. Over time, Niebuhr's observations utilizing Mayer's methods would stand in their accuracy.

Mayer himself divided the angular scale on the instrument that George Huxtable (a retired Oxford physicist and marine navigation historian) spoke of in his letter to Root. Huxtable was kind enough to provide an explanation of the construction and workings of Mayer's astrolabium, or repeating circle. The instrument somewhat resembles a sextant or octant except that it consists of a full 360-degree circle. It could be used to measure horizontal as well as vertical angles, but not both at one time. The repeating aspect is much like using a surveyor's transit in that the backsight is made with zero, the angle is turned, and both motions are locked. The lower motion is then unlocked to resight the backsight with the angle still "in the gun". This is repeated many times. By doing so, the age-old problem with imprecise division marks on the instrument is overcome. By repetition, reliance on reading portions of a degree is reduced to one interpolation. The astrolabium had an innovative micrometer device. Portions of degrees were determined by the number of turns of a screw to cover a degree of arc. The individual turns of the screw were further broken down to units of six. The circle now resides in the Dithmarscher Museum in Meldorf, Germany.

This instrument was both a blessing and at times a curse. Niebuhr and a colleague were nearly torn to shreds by a mob in Egypt, believing this European Christian possessed a machine that would turn their world topsy-turvy upside down (having observed its inverted optics). This happened on enough occasions that Niebuhr became cautious to even use it publicly. On one venture to the Pyramids he challenged an armed Bedouin attempting to steal the "astrolabe". The surveyor bluffed the Bedouin easily once it was obvious the flintlock was not loaded.

Niebuhr's Measurements
Niebuhr constantly plotted and recorded the courses of ships and desert caravans. While at Constantinople, he determined the circumference of the city to be 26,000 paces. While in Egypt, he measured the height of the Pillar of Pompeii to be 89 feet with a base of 5 feet, and documented the use of a "nilometer" to measure the depth of that river. Under threat of robbery and harm, using triangulation, Niebuhr and a colleague measured two of the Pyramids at Giza as well as their orientation. Their measurements of the height of the Great Pyramid differs with modern measurements by 71 centimeters (approximately 2.3 feet). While there, the dimensions of the Sphinx were documented. On one occasion in the Red Sea, he convinced a pilot of the ship carrying him to dispose of the magnet placed between the two compasses (the pilot believed that magnet would restore the "magnetic virtue of the needles"). In Saudi Arabia, while demonstrating a microscope, lice were being observed. The Arabs proclaimed that lice that large could only come from Europe. Niebuhr, while walking beside a donkey, mule, horse, camel or dromedary, logged the amount of his own paces that each of these animals would complete in a given time (half an hour). The length of a camel's pace never changes whether walking or running. Then while riding, he would record a compass bearing as well as time traveled. Many of these excursions weren't just a few miles, but many hundred tedious and uncomfortable miles. In the night, he would correct his location and declination of the needle with astronomical observations. These observations included latitude as well as longitude without a chronometer. Later travelers would marvel at the precision of his mapping technique.

Niebuhr never measured the Red Sea where Moses was said to have crossed. He did cross a portion of it, riding a camel (the depth never exceeding the knees) on a return trip from Mt. Sinai. His colleague Forskall, the botanist, did visit the supposed site of the crossing by Moses in the flight from Egypt. He determined the depth of the sea to be about twelve fathoms (72 feet) with the fluctuation of flood and ebb to be two ells (3.75 feet, plus or minus). His diplomatic conclusion was that the entire incident was indeed a miracle.

The True Circle
With envy and dread, we can look back on the travels of the young scholars in the prime of their lives, filled with curiosity and discovery. They endured cold, unbearable heat, hunger, Muslim prejudice, strange diet, fear and joy, all in their youthful quests to advance the knowledge of the European world. All but one gave their very lives. Permit me to blatantly borrow one of Mr. Hansen's observations. Whether on sea or residing in the deserts of Egypt, Arabia or Iraq; even the marshlands of Germany (where in his later years he was blinded from crude solar observations), Carsten Niebuhr was surrounded by a true horizon, an artificial horizon being a needless encumbrance. Herr Niebuhr lived his honest and humble life within that true circle. Honesty, integrity, a lust for adventure and the quest to convey an accurate record of our world are the traits of our profession--the traits Herr Niebuhr and we all share within this true circle.

C. Barton Crattie holds a BFA degree from Murray State University and is a licensed surveyor in Georgia and Tennessee. He currently serves on the Board of Directors for the Surveyors Historical Society.

A 1.662Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE