If you go to Google Earth and type in US National Arboretum and look inside the arc of Meadow Road between Beechspring Road and Holly Spring Road, you will see, 2/3 of the way to Holly Spring Road, a huge tree, the Pin Oak that sits behind the left-hand birch. It is one heck of a tree. Scroll to the bottom (south end) of the Arboretum and find Maryland Avenue. Follow it til it ends at the US Capitol; the Capitol dome is a bit larger in diameter than the Oak Tree, just a bit. Its the largest tree at the Arboretum, it's just a quirk of perspective that makes the birches seem to be on a scale with it!
I love this view of the birches. If you were to create a triangle of birches in your mind and create the structures of the trees and the spacing, you would be hard put to do better than this. It is like a living triptych. It looks best from this view: that is, on Beechwood Road, halfway between Meadow Road and Azalea Road. You can drive right up to the birches on Meadow Road, but the effect is lost; they're still nice trees but the picture just isn't the same!