In this photo of Pascal Dagnan-Bouveret, the artist is leaning on crutches in front of a very unusual easel arrangement. He seems to be in an indoor-outdoor space. There is at least a partial greenhouse window or frosted glass diffuser overhead and a drape behind him to cut down on reflections.
The easel is mounted on four small railroad wheels resting on a track. There’s also a circular ring under the easel which might allow the easel to turn sideways.
I asked Professor Gabriel Weisberg, one of the world authorities on Dagnan, to comment. He said no specific information has surfaced about this particular photo.
About the crutches, he said, “I don't think he was debilitated in any way when this was taken. It all is part of his steadying himself.” About the rails he speculated that “perhaps he wanted to get closer to actual models or move with changing light conditions as he worked partially outside.”
The only thing I can figure is that he got the idea for using rails from the practice of some sculptors, who rely on railed carriages to move very heavy stones or bronzes in and out of the studio.
Photo from Against the Modern by Gabriel Weisberg