Chapter 8 Chapter 8 Longitude 24 degrees

The measurement of the bottom edge was carried out for a total of thirty-eight days, beginning on March 6 and ending on April 13.With not a moment to waste, the two leaders of the expedition decided to start building the triangle series right away. Firstly, the latitude of the starting point of the measured meridian arc should be determined.The number of latitudes spanned by the measured meridian arc can be known through the difference in latitude. On April 14, the most precise observations to determine the longitude of this place began.The night before this, when the work of measuring the base of the foundation was discontinued, Amory and Zorn had only obtained the heights of many stars by re-measurement of latitude and longitude.The two young men observed so accurately that the interval between each two is only two seconds (angle unit, one minute ∥ sixty seconds), and these intervals are mostly caused by different refractions caused by changes in the shape of the atmosphere.

From these observations repeated so carefully, they deduced, with sufficiently fine approximation, the latitude of the southern end of the arc of meridian: 27.951789 degrees south. The latitude was known, and they began to calculate the longitude, and fixed this on a large-scale map of southern Africa.This map reproduces the latest geographical discoveries of the region, the itineraries of Livingstone, Anderson, Magyar, Baldwin, Wayan, Pocher, Liechtenstein, and other travelers and naturalists.They need to choose a meridian arc on the map that spans several degrees of latitude between two stations.We know that the longer the arc of meridian, the weaker will be the influence of possible errors in measurement in determining the number of latitudes.The arc of meridian from Dunkirk via Paris to Formentera spans nearly ten degrees of latitude, nine degrees fifty-six minutes to be exact.

In the joint Anglo-Russian triangulation experiments, however, the choice of meridians had to be made with extreme care.It must not encounter some natural obstacles, such as mountains that cannot be crossed, and large areas of water that block the progress of observers.Fortunately, this piece of land in southern Africa seemed so perfect for this kind of experimentation.The undulation rate of the ground is very small, and the small amount of water flows easily.They will encounter dangers, but not obstacles. This land in South Africa is occupied by the Kalahari Desert.The Kalahari Desert stretches from the Orange River to Lake Ngami, between 20 degrees south latitude and 29 degrees south latitude, starting from the Atlantic coast in the west, and extending to around 25 degrees east longitude in the east.It was this meridian along the eastern edge of the desert that Dr. Livingston explored in 1849 to Lake Ngami and the Zambezi waterfalls.As for the desert itself, it doesn't exactly live up to its name.This is not the Sahara, as dry and sandy, vegetated and impassable as one tries to imagine.The Kalahari Desert is rich in flora, the ground is covered with rich grasslands, and there is a thick undergrowth and tall woods.Birds and beasts multiply here.Some resident tribes and the Bakarahari live here, and the Bushman nomadic tribe is also frequented here.But water is scarce in the desert for most of the year, and the beds of the many rivers that run across the desert are dry. Dry land is a real obstacle to exploration in this area.But now that the rainy season has just ended, people can use the vast amount of immobile water kept in marshes, ponds and streams.

These are the relevant information provided by the hunter Morcum.He has been in and out of Kalahari many times, either for hunting, or as an accompanying guide for a certain geological exploration.Both Colonel Everett and Strux considered this vast area to be favorable for an accurate triangulation experiment. Now they need to choose a meridian to measure.Can this meridian be taken at one end point of the foundation base, so that there is no need to use a series of auxiliary triangles to connect the base base to another point in the Kalahari Desert. After careful study and discussion of this situation, they considered that the southern end of the bottom edge of the foundation could be used as the starting point of the meridian.This line of meridian lies at twenty-four degrees east longitude, and it passes through a region of at least seven degrees of latitude, from twenty degrees south to twenty-seven degrees south, without encountering any natural obstacles, at least not shown on the map.Only in the north it passes the eastern half of Lake Ngami, but this is by no means an insurmountable obstacle, since Arago experienced greater difficulties when it connected the Spanish coast with the Balearic Islands.

A meridian arc to be measured is selected on the twenty-fourth degree east longitude.In Tsarist Russia in the northern hemisphere, they would have easily measured the length of another arc along this meridian. The experiment began immediately, and the astronomers were busy choosing where the vertices of the first triangle should go, this triangle will have as the base the directly measured base. The first triangle vertex is selected to the right of the meridian.It was a large tree isolated about ten miles away.It can be seen clearly from the southeast and northwest ends of the bottom edge of the foundation (Colonel Everett placed a support at each end of the bottom edge of the foundation).The top of the tree is pointed, and the height of the tree can be measured very accurately.

The astronomers first set out to measure the angle the tree made with the southeastern end of the base's base.This angle was measured with the help of the Poldar-repeated theodolite used in the geodetic experiment.The two optical axes of the theodolite are accurately located on its disk surface, one optical axis is aligned with the northwest endpoint of the bottom edge of the foundation, and the other optical axis is aligned with the lone tree located in the northeast direction.The two optical axes indicate the angular distance between the above two points by their separation.It goes without saying that this well-built instrument allows observers to minimize observational errors.In fact, through the repetition method, these errors compensate each other and cancel each other out in the case of repeated repetitions.As for the vernier scales, spirit levels, and vertical lines that ensure proper placement of the instrument, there is nothing unsatisfactory about them.The Committee had four repeating theodolites, two for geodetic observations, such as measuring angles, and two with vertical dials, capable of measuring zenith distances with the aid of artificial horizons, so that a certain distance could be calculated by approximation even at night. A point of latitude.In this large-scale triangulation experiment, it is not only necessary to obtain the degree of the triangle angle of the earth, but also to measure the meridian height of the stars, that is, the latitude of each observation point.

The work started on April 14th.While Colonel Everett, Zorn, and Ballendre calculated the angle formed by the southeast end of the base of the foundation with the solitary tree, Strux, Amory, and Lord Murray measured it at the north-west end to the same tree. The angle formed by the tree. At the same time, the camp was withdrawn, the cattle were harnessed to the shaft, and the expedition team, under the leadership of Morcum, walked towards the first observation point as a resting place.Two kamas and their drivers are responsible for transporting instruments and accompanying the observers. The weather is relatively clear and suitable for experimental operations.It had been decided that, should atmospheric conditions interfere with the determination of the position, they would make observations at night with the help of reflectors or electric lights provided by the Commission.

During the day, two angles were measured and the results were carefully checked and recorded in two notes.As night fell, the astronomers and expeditions assembled under the lone tree that served as a pole. It was a gigantic boba tree, with a trunk over eighty feet thick.The rock-colored bark gives it a peculiar appearance.Its fruit is ovate, with white flesh, and countless squirrels who like to eat this fruit live in its dense branches and leaves.At the foot of this giant, the entire expedition has a place to rest.Meals are prepared by an on-board cook who is never too embarrassed to cook without rice.Hunters hunted several antelopes nearby.Soon, the smell of barbecue permeated the air, arousing the appetites of the observers who did not need to be stimulated.

After a nutritious meal, the astronomers went to rest in their own cars, while Morcum set up sentries around the camp.The fires lit with boba boughs burned all night, keeping beasts that came looking for flesh and blood at a respectful distance. But after two hours of sleep Zon and Amory woke up.Their work is not over.They have to calculate the latitude of this observation point by observing the height of the stars.Regardless of the fatigue during the day, the two started working in front of the astronomical telescope.The wild laughter of hyenas and the roar of lions are echoing in the dark field.The pair accurately measured the travel of the zenith from the first observation point to the second observation point.