the British John Constable and the American Asher B. Durand. In 1826, Constable painted "The Cornfield;" 19 years later, Durand painted a similar work, "The Beeches." And so the comparison ...

The Beeches, 1845. Artist Asher Brown Durand. (Photo by Heritage Art/Heritage Images/Getty Images) When ecologists want to know how much nature has changed over the years, they compare data from ...