Circa 1720/1730. Red Chalk Drawing. Portrait Of Jean Bernoulli, Mathematician

Jean Bernoulli (1667–1748) was a Swiss mathematician and physicist, a member of a renowned family of scientists, known for his fundamental contributions to infinitesimal calculus, his correspondence with Leibniz, and his work on exponential calculus.
He was a member of the most important academies in Europe, such as those in Paris, London, and Berlin, as well as in Saint Petersburg. 
This portrait appears to have been engraved by Étienne Ficquet in France.
The engraving bears the inscription “J. Ruber (or Raber) pinxit.”
It is curious that, for the time being, no trace of this artist can be found. 
Perhaps this is due to an erroneous transcription of the name by this famous engraver.
We are also presenting a portrait of Christian Wolf, mathematician and philosopher, by the same artist. 
The work is very well drawn and set in a very simple frame from the 1920s.
Dimensions of the drawing: 13 cm x 8.5 cm