Preliminary drawings for the observations of the Venus transit across the solar disc

Among the scientific activities carried out by the members of the “Italian Spectroscopist Society” there was also the organization of the expedition to India to observe the rare astronomical phenomenon of the transit of Venus across the solar disk, in 1874. It provided, in fact, the opportunity to measure with great precision the solar parallax, from which one could then derive the distance of the Earth from the Sun. Drawings show the calculations of the timings of the various contacts between the shadow of Venus and the solar disk as it would be seen from the four villages of the east coast of India, between Madras (today's Chennai) and Calcutta, among which they were looking for the most suitable observational location.