Ever noticed that some of the nicest places to sit on the National Mall are around the edges, gardens such as the one outside the Botanical Garden building, or the sweet little swamp and wetlands next to the Smithsonian’s National Museum of the American Indian? The designers of the new National Museum of African American History and Culture went before the Fine Arts Commission with some initial ideas last week, including a naturalistic water feature along Constitution Avenue. I think it’s a great idea, another softening of the rigid edges of the imperial Mall. But not everyone on the commission agrees. I take up the subject in my first entry for the Post’s new arts blog, here.