Australian watchmaker F. Allerding recorded the “black-drop” effect as the silhouette of Venus prepared to exit the Sun’s disk on December 9, 1874. He observed through a 3½-inch refractor. Adapted from Observations of the Transit of Venus Made in New South Wales by Henry C. Russell (Sydney, 1892). (Click on the image for a high-res version.)
Courtesy Institute for Astronomy, University of Vienna.