What is a Black Drop?

This happens when the dark edge of Venus has just entered the face of the Sun, or is just tangent to it upon leaving. What keen-eyed observers see is that in stead of a bright sliver of light between the edge of the Sun and the black disk of Venus, they see the edge of the Sun bend inwards and touch the disk of Venus as though Venus is a black droplet. Figure 5 and 6 below, show what this looks like from a sketch made during the 1769 transit.