The Northern Lights, page 22
The men stayed just a few days in the city, long enough to arrange transport to Omdurman, to set up a bank account, and to meet the Norwegian consul, Mr. Hooker. Birkeland sought his advice on buying a property in Egypt but he proved unhelpful and Birkeland left disappointed. However, at Shepheard’s Hotel, the unofficial embassy, post office, luggage room, club, and office for European visitors to the city, Birkeland met the Danish consul, Dr. Eriksen. The two men instantly took a liking to each other and Eriksen promised to look into property matters for Birkeland. The consul was fascinated by Birkeland’s plans to study the Zodiacal Light and made him promise to visit him in Cairo on his return to relate all that he discovered in the Sudan.
The journey to Omdurman was surprisingly easy. They took a night train from Cairo to Aswan, the most southerly town on the Egyptian Nile, where they were joined by a number of European tourists for the final few kilometers of track, which skirted the Aswan Dam and terminated at the banks of the Nile beyond the First Cataract. From here, small boats carried the tourists to the semisubmerged pillars and courtyards of the Philae Temple, past hieroglyphs and monumental gateways and over the sacred sanctuaries and statues of the gods lying beneath the translucent green waters of the Nile. A short carriage journey took them to the Nile steamer that carried them up the majestic river to the impassable Second Cataract and the bustling village of Wadi Halfa. Here, the railway recommenced and crossed the desert to Khartoum. The incongruous train line, over eight hundred kilometers long between Wadi Halfa and the capital of Anglo-Egyptian Sudan, passed through unbroken, unpopulated desert. It had been constructed by Lord Kitchener about twenty years before in order to capture the Sudan from the Muslim Mahdi, bringing it under the “protection” of the Egyptians and British. During the major battle of the campaign, 11,000 Mahdists were slaughtered by the superior firepower of the Anglo-Egyptian force, who lost only forty-eight troops. Kitchener burned the Mahdi’s body in the furnace of a steamship and contemplated using his skull as an inkstand. Birkeland had heard this story: it had been a source of disquiet in Norway. Perhaps this colored his judgment of the British administration of the Sudan and, particularly, of its leader: “The governor of the city of Omdurman is a young noble Englishman. When talking he often seems somewhat embarrassed although he rules the city with a firm hand.”
The train arrived in Khartoum, the bustling capital built where the Blue and the White Niles converged. A little to the north, on the east bank of the Nile, was situated the more ancient city, the former capital, Omdurman. Omdurman was at the crossroads of several trade routes across Africa. The large market square teemed with camel sellers, ivory and spice merchants, goldsmiths, horse dealers and slave traders, farmers and tribesmen from southern Sudan and beyond, Nubians and Tuareg. During the mornings, women could be seen haggling at the stalls, some seminaked, others swathed from head to foot in black or white cloth, faces and even eyes often concealed behind metal visors and close-link chain mesh. Despite the variety found at the market, Omdurman itself was suffering from several years of poor harvests, and durra, a grain with which bread was made, was selling for ten times the price it had fetched four years earlier. Most inhabitants lived at subsistence level by keeping a few animals. As Birkeland observed in an article he wrote for the newspaper Aftenposten, after he had been in Omdurman for a few weeks:
There are a considerable number of cows, goats, and sheep at Omdurman. Each day thousands of animals are led out in the morning and in the evening they return in a cloud of dust exactly at sunset.
To accompany the article Devik took photographs: of the view from their balcony, a holy man, a water carrier, and other sights that struck him during the first few weeks. Birkeland gave a taste of their living and working conditions for the readers:
Skolem, Devik, and I are living in a comfortable house with three rooms, a large balcony and an outhouse. I have rented it from a Greek and furnished it in a simple manner. The house is situated on the outskirts of Omdurman close to the desert, a location favorable for our observations. When observing the Zodiacal Light at night, the wind is often so strong that I, in contrast to my assistants, am not able to stay on the roof of our house but instead prefer a site by a wall, somewhat further out in the desert.
The last photograph in the piece was of Birkeland himself, dressed from head to toe in a prophet’s costume with a turban and glittering galabiyya. As he wrote, “The turban is from Mecca and in Arabic silver letters is written ‘the prophet’—in Norwegian, in order not to insult the Arabic silversmith.”
Although taking time to explore the city, Birkeland was impatient to begin observations of the Zodiacal Light. First, however, he had to surmount an unexpected obstacle. He had assumed that the ancient city of Omdurman would be barely electrified, but street-lights were widespread and ruined their observations of the Light. In order to see the Zodiacal Light better, Birkeland sent a letter to the assistant governor of Khartoum with a very unusual request:
October 1913
Dear Mr. Sandford,
I have come especially to the Sudan to study the Zodiacal Light because the origin of this has not yet been discovered.
We are working from sunset until 9 P.M. and from 3 A.M. to 5 A.M. each night for twelve nights after each new moon. We wish to photograph the Light but the lamps in the streets make this impossible and I should be very much obliged if you would kindly arrange for the lights (as shown in the attached plan) to be extinguished by 3 A.M. each morning.
Yours very sincerely,
Kr. Birkeland.
Mr. Sandford obliged, and the three scientists began their observations in earnest. Even without the street lamps, to see the Zodiacal Light they had to keep the lights turned off in the house after sunset to allow their eyes to grow accustomed to the dark before venturing into the desert. The subtle phenomenon appeared about one hour after dusk above the western horizon and one hour before sunrise above the eastern horizon, so the scientists lived a nocturnal existence. It appeared softly as their eyes adjusted to its ethereal presence, an elongated pyramid of pale light that reached from the horizon far up into the night sky. There had been reports of the Light making a complete arch over the sky to the opposite horizon, although Birkeland did not observe this. The pyramid of light was not exactly at right angles to the horizon but tilted about ten or fifteen degrees and appeared to glow with a constant intensity until it faded after an hour or so as the Earth turned. The opposite occurred before dawn. The darkness was gradually illuminated by the column of light about an hour before dawn until the Earth turned sufficiently for it to be swamped by the bright dawn light.
The first person to write about the Zodiacal Light, observed on 18 March 1683, was the eminent Italian astronomer Giovanni Domenico Cassini. He saw a cone of brighter sky that stretched up from the horizon along the ecliptic of the celestial sphere, on which were also situated the constellations of the Zodiac—hence the name he gave to the phenomenon. Cassini’s explanation, that the Light was caused by sunlight scattered off small particles orbiting the sun, was still considered valid when Birkeland set out to study it further. He agreed with Cassini that a substantial constituent of the Zodiacal Light was created when light illuminated the disc of dust particles that spread out from the sun. The effect seen from Earth was similar to a beam of sunlight illuminating a dark room through a narrow gap in the curtains. Specks of dust could be seen dancing in the beam but not beyond it, although dust was there. If the beam fell directly on the viewer, no dust would be seen either for the eye would not perceive it against the intensity of the sunlight. Similarly, the Zodiacal Light was seen only from the night side of the Earth, without the interference of direct sunlight. The dusty disc was thought to be lens-shaped, or like a fried egg, as if the sun were the yolk and the dust the white. It rotated around the star along with the planets embedded in it.
Unlike Cassini and most other observers of the Zodiacal Light, however, Birkeland also believed that a small but significant constituent of the Zodiacal Light was not caused by light bouncing off dust, but by light being deflected by electrons emitted from the sun’s surface—the same electrons that caused the Northern Lights. He had read in earlier reports about the Zodiacal Light, particularly that of the American Reverend George Jones, published in 1856, that it pulsated or was not entirely constant. Birkeland surmised that light particles, or photons, traveling from the sun would hit the electrons and be deflected. A number of them would reach Earth and, Birkeland hoped, could be measured. However, photons deflected by the dust particles would also be measured. The only way to distinguish between them was to observe whether there was any variation in the number of photons detected. The light emitted by the sun was constant, a fact established by two scientists, Langley and Abbot, in America, in 1881, and confirmed many times subsequently. They used a spectrobolometer, which measured the relative intensity of the spectrum, and a pyrheliometer that calibrated the results, to show that the number of photons emitted by the sun varied by less than 1 percent, if at all. If there were rapid variations in the Zodiacal Light, this would be caused by irregular emissions of charged particles from the sun that would scatter the photons. The same particles would also cause magnetic storms, which Birkeland hoped to record with the magnetometers he had brought with him. If he could find a way to accurately record variations in the Zodiacal Light, he would have the indisputable evidence he needed that cathode rays were emitted from the sun.
To begin this process, it was important to know more about the dusty disc and the Zodiacal Light. Birkeland and Devik made many drawings of the Light pyramid in relation to the horizon and the stars. They could gain an impression of variations in the Zodiacal Light by comparing it to the stars. The intensity of starlight was first categorized by the ancient Greek astronomer Hipparchus in the second century B.C. He made a catalogue of about a thousand stars in six categories designated by numbers, with 1 being the brightest and 6 those just visible. In 1856 a British astronomer, Norman Pogson, proposed the numbers to be “stellar magnitudes” described mathematically. He calculated that each number represented a two and a half times increase in brightness; thus a star of 1 was 2.512 times brighter than one of 2 and the difference between 1 and 6 was a 100 times brightness. His mathematics made it possible to have subtle fractions of magnitudes and to extend the scale into negative numbers, as with the sun at −26. Birkeland and his assistants used Pogson’s scale to note the overall intensity of the Zodiacal Light and any variations they perceived. In February, for example, the Zodiacal Light stretched from the constellation of Aquarius to Pisces, and the stars of Pegasus were visible through the Light to the upper right, whose intensities varied from 2.5 (Markab) to 2.8 (Algerib).
Birkeland also hoped to map the distribution of the Zodiacal Light in space with hand-drawn sketches. For the drawings to be useful, the observers’ impressions of the outer limits of the Light needed to conform to the same standards. To practice this, Devik and Birkeland would draw the phenomenon at the same time but from different places, in order to compare the similarity of their drawings. After the first few weeks it was hard to tell them apart. Birkeland was planning to send Devik to Rhodesia or South Africa the following year in order to make simultaneous observations of the Light from a distant location.
As well as making drawings, Birkeland attempted to photograph the subtle phenomenon to see whether the variations in light intensity would register across a series of plates. Unfortunately, the exposure time needed to register an image was so long that any hope of seeing variations was abandoned. Birkeland set his mind to finding an alternative method, meanwhile setting up the magnetometers to trace any correlation between variations in the Light and movements in the magnetic field. He kept the equipment in a sturdy canvas tent outside, as it was too difficult to remove all iron objects, which would affect the readings, from their house. Skolem and Devik guarded the tent all night from the curious locals who would come and sit near them, saying nothing but watching every movement. Theft was common in Omdurman and Birkeland became the target of a number of attempted burglaries. His house servants—he paid seven as an act of charity, although only two actually worked— tried their best to keep the house secure but in the end Birkeland was advised by Mr. Sandford to buy a gun. He bought a 7.6-bore revolver in February and kept it under his pillow at night, an act that brought the subject of defense back into his mind.
Two days after receiving a license for his new gun Birkeland wrote two letters about his electromagnetic cannon. The first was addressed to the Right Honorable Lord Rayleigh, fellow and former president of the Royal Society, winner of the Nobel Prize for Physics in 1904 and president of the Commission for the Examination of Inventions of War. The second, similar in content to the first, was sent to Dr. Glazebrook, who was also on the commission and whom Birkeland had met during a trip he had made to London in July 1906 to explain the principles of his fertilizer furnace at the invitation of the Faraday Society. During his brief sojourn in England, Birkeland had attended a lecture at the Royal Society.
Dear Dr. Glazebrook,
I have seen from the newspapers that there was a meeting in Mansion House on Saturday 5th, discussing how to protect England from airships. Do you remember that I made allusion to an invention for such a purpose some years ago after a meeting at the Royal Society? The same invention may also be used in the navy as it is easily installed in battleships.
If you think my invention would interest military authorities in England, I will give further explanations. Perhaps the best would be to explain the invention to Lord Kitchener in Cairo. He would certainly be one of the best judges in the world. There are three conditions:
1st Absolute discretion. My name must never be used in connection with the invention.
2nd When the model is ready and adopted, it shall be given to the Norwegian state without costs.
3rd The arms must never be used against the Scandinavian peoples.
I am here in Omdurman studying the Zodiacal Light. Please send your answer to Professor Birkeland, Aswan.
Yours sincerely,
Kr. Birkeland
Birkeland asked for complete discretion because he had begun to fear that his invention of the gun could lead him into danger. Frequent military skirmishes between the major European powers, particularly between the French and the Germans, had caused him to worry that he would be seen as a threat as long as he was free to offer his invention to any government he chose. To solve this situation, he decided to offer first refusal to develop the cannon to the British, who were now linked to Norway through Norway’s Queen Maud, who was the daughter of King Edward VII. Birkeland hoped, therefore, that the British would be the least likely of any European power to use the cannon against his own people. Glazebrook was requested to reply to Aswan as Birkeland planned to return along the Nile to Helwan in the early spring, stopping in Aswan to make observations.
Birkeland worked hard and productively during his time in the Sudan; he wrote papers for The Cairo Scientific Journal and the French Academy’s publication Comptes Rendus, about his preliminary research into the Zodiacal Light, and his relationships with Devik and Skolem were close and fruitful. With Skolem, Birkeland made theoretical calculations and mathematical models of the density of the Zodiacal Light, pioneering work necessary to deduce the shape and structure of the dusty disc. Comparisons of the model with their observations confirmed that it was indeed disc-shaped and extended at least beyond the Earth. There was no way to measure exact numbers of dust particles in any particular area of the disc; as a result their model resembled a map without a scale, showing the size of features and contours relative to each other rather than in absolute terms. They estimated, however, that the dust particles were microscopic and the density very low, about twelve grains per cubic kilometer of space. The sparsity of the dust grains in the disc made it invisible except in the ecliptic plane, right across the white of the egg, where the tiny numbers of particles added up to millions because the distances involved were so great. Even in perfect viewing conditions, the Zodiacal Light was one million million times less bright than the sun, one million times less strong than the moon, and around 10,000 times weaker than a strong aurora.
As for the oscillations that Birkeland was keen to measure, these were elusive to record although he was sure he saw them with the naked eye. On some nights the variations might have been due to atmospheric smoke and dust from the desert that intermittently obscured the Light. Bright starlight also interfered with the observations, and their recording efforts were frequently impeded by high winds and buffeting sand. Even though Birkeland tried using different varieties of plate and lens to shorten the exposure time for photographing the Light, the improvements were minimal. It was frustrating to be unable to record what he was convinced he saw with the naked eye.
Despite the warm weather and enjoyable challenge of the work, Birkeland’s health had not greatly improved since his arrival in Africa. The lack of sleep from night-time observations was making him nervous and edgy, but on the nights when the full moon obliterated the Zodiacal Light and he could have caught up on his sleep, he still suffered from insomnia. His drinking also increased.
The amount of soda Birkeland drank might have been explained by his suspicion of the drinking water in Omdurman:
I learned recently to my horror that Omdurman has a lot of leprosy. Among the 45,000 inhabitants of the town, there are around 100 leprosy patients who are not kept isolated, but live among other people and eat from the same pans. Several of the sick are allowed to serve as water porters in the town. Close to our house is a public water tank, filled several times a day by a leprous woman. I have seen her cleaning the tank with her diseased arm and adults as well as children drink that water!
