Adam Hughes writes "I'm rebuilding this very bike. The fellow at the rear is Anzani, the build on this motorpacer is about 1902."
The "rocket" is a radiator for the watercooled Aster 6 1/2hp engine. Aster is clearly visible on the crankcase. Motorcycles 1867-1930
Sourced from the Bibliothèque nationale de France by Isabelle Bracquemond