Rare edition of XVIII of the century "Lettres à une Princesse d'Allemagne sur divers sujets de Physique & de Philosophie" (1768) Written by Leonard Euler (Leonhard Euler) Place of publication: St. Petersburg, Imperial Academy of Sciences Year of publication: 1768 The First (Tome Premier) Description: It offers a rare and valuable publication of the letters of famous mathematician and physicist Leonard Eyler addressed to the Princess of Germany, a unique combination of scientific thought about physics and philosophy in the form of letters. This original publication, published at the Imperial Academy of Sciences in St. Petersburg, is a clear indication of the scientific and cultural heritage of the XVIII century. Status: The original cover is missing, the title page and the main sheets are saved. Collectible value: The book is of interest to collectors of ancient books, historians of science and lovers of the Enlightenment. This publication is especially valuable due to its unique connection with Russian history and the activities of Leonard Euler in St. Petersburg. Leonard Eyler, a prominent mathematician and physicist of the XVIII century, wrote a series of 234 letters between 1760 and 1762 addressed to Princess Friederica Charlotte Brandenburg-Swedt and her younger sister Louise. These letters, originally written in French, were published in two volumes in St. Petersburg in 1768, and the third volume was published in Frankfurt in 1774. In his letters, Euler sought to explain complex scientific concepts in accessible language, covering the topics of physics, philosophy and astronomy. For example, he began by discussing the concept of "size", defining units such as foot and mile, and moving on to discuss the size of the Earth and the distances to the planets of the solar system. These letters are considered to be an outstanding example of XVIII-century scientific and popular literature intended for a wide audience, and they have been commended for their clarity and ability to convey complex ideas to lay-offs. Petersburg. It is a rare and valuable copy reflecting Euler's scientific heritage and his contribution to the popularization of science.