(7) As the result of frequent and familiar communication that the Prince conducted with him and the intimate friendship which was the result bonded them and he sincerely regretted the recognition of the loss which was due to everything that Mr. Euler had contributed to the cultural and spiritual enlightenment of the Margrave's daughters. He provided them with lessons and it was for them that he wrote during his stay at the Marburg Court the letters concerning various subjects of physics and philosophy which he had published after his return to Saint Petersburg.