Claude Monet at Work in His Garden, 1915
openculture.com
openculture.com
The idea prevailing at the time (which partly came from the physiology of vision actually) was that, on one's first impression of something, the brain only perceives patches of color (a 2D image), that are only processed after a split second into something more resembling a 3D representation. Impressionists tried to capture that supposedly "pure" first image. Everyone tried to do it in his/her own way. Seurat, for example developed pointillism (http://en.wikipedia.org/wiki/File:Seurat-La_Parade_detail.jp...).
Look at him walking and the dog too they're walking way too fast very unnatural but really it's not much of a difference I guess.