Atget's example is that of darkness into light and light into darkness. It's the stretching out of light, time, into a single moment. It's clear and concise. Not as a single thing but as a constant transitioning from one state to the next. A ton of feathers is just as heavy as a ton of steel but they don't feel the same. That's how Atget's treatment of light and dark feels to me here. As something equal in weight but different in texture.