From the 58 original letters from Herény (Hungary) and the copies of 12 replies written in the "Kopierbuch", Heidelberg by Max Wolf, we can follow the cooperative activity of two European specialists in the development of observation technology in the new science, astrophysics.

Based on the century-old documents we can retrace the development of the relationship between Gothard and his younger colleague working in the creative atmosphere at the University of Heidelberg, which was only a scientific connection at the beginning, but later it grew to be a friendship. Contemporary documents from the end of the 19th century have preserved the everyday questions of the two experimenting scientists as they were working to reveal the secrets of the Universe with the help of photography and spectroscopy.

Astronomical instruments are made custom-built for thought-out and clearly determined research goals after determining necessary precision. The most intricate details of such a process are revealed when reading the letters of Eugene von Gothard and Maximilian Wolf. We can follow the details of how the transit instrument of Heidelberg was born in 25 letters, on 78 pages. In Eugene von Gothard and Max Wolf's discussion, apart from working out modern technical solutions necessary for the scientific task, accurate determination of time and localization, there are also a lot of references to the contemporary industrial background, which was indispensable for constructing the perfect instrument.