This painting mostly focuses on movement and gesture. The way the theme, movement is tackled in this piece, is the way Honore put the figures bend forward against the wind depicted on the canvas, almost imaging them moving and pushing them self to go forward. Also we see the motion of the wind in the drapery folds of the figures' clothes, the woman's bundle and the child's hair blown from the weather. The mother's neck and arm are not at a normal proportion, but exaggerated.
I think Daumier did this to show, from his mind, how the wind was so strong against the mother and she was pushing as much as she can, that she was being stretched because of the two forces opposing each other. There is a contrast were the light illuminates the mother's upper half and her load, leaving the rest of her body and the child in shadow. In my opinion this contrast gives the mother, the focal point of the piece, showing lines of her body (lines moving against her skin).
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