But before all these events, tragic or happy, Niels had a career to build. So let's go back to 1917.

        As with the teaching position in theoretical physics, Niels decided to move heaven and earth to obtain the creation of an institute devoted entirely to this scientific field. Begun in 1917, his campaign to obtain the necessary authorizations and funding was successful in 1918: the university then gave its agreement and friends of Bohr managed to raise sufficient funds. All that remains is to find land; the city of Copenhagen will provide it. 

        In the fall of 1918, Niels Bohr wrote an enthusiastic letter to Ernest Rutherford announcing his project and asking him if he would agree to chair the inauguration of the new institute. He is optimistic about opening a year later. But this announcement intersects with a letter from Rutherford, in which the latter offers his Danish friend a position as professor of mathematical physics at the University of Manchester. 

        Niels panics: the future that seemed clear to him in Copenhagen is perhaps not the only way to advance his research. What should he do? To respect the confidentiality requested by Rutherford, he does not tell anyone: with Margrethe, he goes to his brother, Harald, and spends the night discussing the pros and cons of each option.

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     A few days later, on December 15, he sends his reply to Rutherford:

    « I don't know how to thank you for your letter of November 17, which I have just received and which besides being the source of the greatest pleasure to me has at the same time been the object of sorrowful consideration.

     « You know that it has always been my ardent wish to be able to work in your neighborhood and to take a part in the enthusiasm and imagination which you impart to all your surroundings and of which I have so much benefitted myself. At the same time I am not in a position to accept the splendid offer, and for which I feel more thankful than I can express because of the undeserved confidence in me that it contains.

    « The fact is that I feel I have morally pledged myself to do what I can to help in the development of the scientific physical research here in Denmark, and in which the small laboratory will play a part.

     « I should like so much to settle down in Manchester again and I know it would be of the greatest importance to my scientific work, but I feel I cannot accept the post you write about because the university has done all that they could to place all external means necessary for my work. Of course the pecuniary means, personal allowance as well as that to the running of the laboratory, will be far below the English standard.

     « I feel it is my duty here to do my best, though I feel very strongly the result will never be the same as if I could work with you. »

 

        Back from his Christmas vacations, Rutherford writes to Bohr : 

       "I hope you will not prejudge the question before you have a chance of coming to England to talk things over. I hope you will do so as soon as it is convenient to travel. There are many things in general I want to talk to you about."

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      Due to the requisitions of ships and trains to repatriate demobilized soldiers, this trip to England was postponed until the following July. The "things in general" that Rutherford wanted to discuss with Bohr concerned his appointment to Cambridge, his latest results, which seemed to show that he had succeeded in disintegrating atoms and, of course, the proposal he had made to Bohr to work together (whether in Cambridge rather than Manchester changed nothing).

       Bohr congratulated his friend on his new position, he became passionate about his experiments with the decay of nitrogen or oxygen atoms by bombardment by alpha particles... and he confirmed his refusal to come and settle in England.

         It was therefore in Copenhagen that Niels Bohr continued his career, in an institute of theoretical physics whose design and construction he supervised with great rigor. Delays and an increase in the cost of construction led him to request additional funding from the Carlsberg Foundation (which he obtained) and to postpone the inauguration until September 18, 1920. That said, this date was chosen because it suited Ernest Rutherford, but the building was not yet fully completed. It would not be until January 18, 1921, becoming one of the world's leading places for the study of quantum physics.

It would not be until January 18, 1921, the day on which that Bohr, without any delay, moved his papers and books into his new domain. That same day, he wrote his first letter sent from that address—a letter addressed, of course, to Ernest Rutherford.

 

         The official inauguration, attended by the university rector and the Minister of Education, would, however, take place on March 3 of that same year. The Københavns Universitets Institut for Teoretisk Fysik would then become one of the world’s leading centers for the study of quantum physics.

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