The Black Drop Effect

What it is

This engraved plate, published around 1761, shows drawings by the Swedish scientist Torbern Bergman of the "black drop effect" — an optical phenomenon seen when Venus crossed the Sun's disk. It appeared in the Philosophical Transactions and was engraved by J. Mynde.

Why it matters

Torbern Bergman was part of the Swedish scientific community connected to Anders Celsius, who had died in 1744. The black drop effect puzzled astronomers observing the transit and shows the kind of careful visual recording scientists of this era relied on before photography existed.

Look closer

• What do the labelled points in the diagrams suggest the artist was trying to measure or explain?
• Why might an unusual visual effect like this have been worth recording so carefully?
• What does this drawing reveal about the limits of observing with the human eye alone?