Milankovic continued his work on the study of the influences of secular variations of the elements of the Earth’s orbit on its insolation and the temperature changes that result from it at different latitudes and developed formulas for calculating the average insolation. His published results were of interest to many scientists in the world.
He received a letter on September 22nd 1922 from Wladimir Köppen, the world famous climatologist and head of the Naval Meteorological Observatory at Hamburg, inviting him to collaborate on a book entitled Paleoclimatology, which he had begun writing with geophysicist Alfred Wegener.
He asked of Milankovic to expand his studies from 130,000 years to 600,000 years. Milankovic agreed to calculate the secular progress of insolation of the Earth at the outer limit of the atmosphere for the past 650,000 years for parallels of 55, 60 and 65 degrees northern latitude, where the most important events of the Quaternary glaciations occurred. He informed the Academy of his results on November 13th 1922 and published them in the Gazette of the Royal Serbian Academy, in order for them to be cited in Köppen and Wegener’s book.
Text about the postcard
He wrote about the first postcard which he received from the German climatologist Köppen:''Some day this simple postcard, which I keep as a relic, shall be preserved in my estate. The postcard was sent from Hamburg by Wladimir Köppen, the great German climatologist, and in it he discussed my recently published theory. Some 49 letters and postcards would follow in succession, and so our mutual correspondence consists of some hundred letters.''
Alfred Wegener formulated his continental drift theory in 1910. The continents had formed a single continent, Pangaea, and then drifted apart and reached their current position, changing thus their position in relation to the Earth’s poles and thus climate zones. During that time the Earth’s rotational axis had not significantly changed its position in relation to the ecliptic plane along which the Earth moves, orbiting around its axis and the sun.
He regularly donated his works to the University Library in Belgrade.
The development of global tectonics conclusively explained the continental drift mechanism only in the second half of the 20th century. Magma constantly seeps from the Earth’s depths through the cracks in the Earth’s crust in oceans. It is transformed into rocks by cooling and pushes against older rock layers, which move towards continents. Colliding with the continental mass, huge blocks of rock slowly slip under the continents and push them. Since deep parts of continents lean on the upper layers of the Earth’s crust, the continents together with a part of the upper layer of the Earth float along the fluidal base of its layer. This proved that the Earth’s poles do not shift, but rather continents change position in relation to the poles, moving along the Earth’s surface.
He was elected a corresponding member of the Serbian Royal Academy and the Yugoslav Academy of Sciences and Arts in Zagreb in 1925.
His first speech at the Serbian Royal Academy was given on March 07th 1925 with the topic ''Calendar of the Earth’s Past.''
Milankovic’s results became known to world science.
Wolfgang Soergel, a professor in Breslava and Freiburg, in 1925 wrote in his work Analysis and Absolute Chronology of the Ice Age: ''Rarely have two attempts at solving the same problem, completely independent of each other and undertaken with completely different starting points, lead to such complementary results. Therein lies the guarantee of the correctness of the analysis of the ice age done in these systems; they support each other. I consider the astronomical analysis of the ice age to be proven and the problem of the absolute chronology of that period to be solved''.
Köppen proposed to Milankovic on December 14th 1926 to extend his calculations to a million years and to send his results to Barthel Eberl, a geologist studying the Danube basin, as Eberl’s research had unearthed some pre-Ice Ages before over 650,000 years. Eberl published all this in Augsburg in 1930 together with Milankovic’s curves.
Köppen invited Milankovic to write an entire chapter for the first volume of the Handbook on Climatology on the astronomical basis of the problem of climate in 1927. This work represents the complete solution to the basic problem of ice ages going back 600,000 years. After intense discussions with Köppen and Wegener, the manuscript was completed in 1930. The work entitled Mathematical Science of Climate and Astronomical Theory of the Variations of the Climate was published in German as a separate book, and the Russian translation came out in Moscow in 1939.
In November 1929, he received an invitation from Professor Ben Gutenberg from Darmstadt to collaborate on a ten volume handbook on geophysics and to publish his views on the problem of the secular variations of the Earth’s rotational poles. After a lively correspondence,
it was decided that for the first volume Milankovic should write about the position and movement of the Earth in space, the Earth’s rotation and the tilt of its axis and secular variations of the Earth’s poles, and for the ninth volume about secular variations of the Earth’s climate. The calculation of secular variations of astronomical elements of the Earth’s orbit was done by Vojislav Miskovic, a professor of astronomy and head of the University Astronomical Observatory. He included new data by Joseph Devaux on the reflection capacity of the snow covers in the new calculation of climate change and the limits of permafrost.
He presented his results also at the Serbian Royal Academy. The lecture on the apparent shift of poles was held at a congress of Balkan mathematicians in Athens in 1934.
He published an article dedicated to the work Alfred Wegener in 1934 after his death during an expedition to Greenland.
Milankovic kept all his correspondence, through which one can follow the development of his ideas. These letters are kept in his archives in the Serbian Academy of Sciences and Arts. The translations of about a hundred selected letters which he received from the most prominent geologists, climatologists, paleontologists and geophysicists of his time were published in the Selected Works, volume 6.
A letter from Soergel, dated January 24th 1931, which confirmed that his field results agree with Milankovic’s calculations. Soergel published his monograph Ice Age in 1938 and based on Milankovic’s curves determined when the Heidelberg man had lived.
One of Milankovic’s admirers, the young geologist Zoiner, a Jew who had fled Germany to London had written in German a dissertation entitled New Results of the Astronomical Theory of Climate Change and as he could not publish it in Germany, it was published in the Gazette of the Serbian Royal Academy in Serbian, in Milankovic’s translation, and in German in the Bulletin of the Serbian Royal Academy in 1938 and 1939 respectively.
Zoiner’s work included an overview of literature (pg. 684-685) from which Milankovic was able to see who was using his results.