The life of a scientist is multifaceted and unpredictable: discoveries, observations, experiments, implementation of the most daring ideas. The names of the most talented and diligent researchers will forever remain in the history of science and the development of human thought. And we use the results of their work every day, sometimes without noticing it. The book you are holding in your hands was created with the purpose of telling about one very modest and at the same time incredibly outstanding scientist of the 19th century - Boris Semyonovich Jacobi. During his life, this tireless researcher accomplished a huge amount of work that brought him worldwide fame and respect from the scientific community. And thanks to his persistent desire to derive practical benefit from each of his work, Russia, the country that he loved with all his heart, acquired many new technologies. The results of Jacobi's work were appreciated and used in science, industry, construction, art and even military campaigns! How could one person have such a diverse knowledge and interests? This will be discussed further. I would only like to note that Boris Semyonovich gave all of himself to each of his work, put his whole soul into each of his inventions, without demanding anything in return. His goal was not to perpetuate his name, but to benefit humanity and science. Not everything in the life and research activities of Boris Semyonovich went smoothly; many trials awaited him along the way. But remaining true to himself, an honest and hardworking person, he overcame them all, leaving behind a good memory and outstanding inventions.