Robert Cornelius performing a chemical experiment, December 1843. This daguerreotype was used as an illustration in James Curtis Booth, The Encyclopedia of Chemistry (Philadelphia, 1850).

Note the glass rod used to stabilize his arm. Two other images were made during this session, one of Martin Hans Boye performing chemical experiments as well as a portrait of Boye.

The fact that exposure times were faster in 1843 and the careful pose make it unlikely that this is a self-portrait. It is more plausible that another person present, for example Martin Hans Boye, took the image.