This section is from the book "The National Capitol. Its Architecture Art And History", by George C. Hazelton, Jr. Also available from Amazon: The National Capitol Its Architecture Art and History.
At the head of the western staircase leading to the Senate galleries is a full-length painting of George Washington. On it we read: " C. W. Peale, pinx! Philadelphia 1779." It was commenced in 1778, when Washington was forty-six years of age, while the army lay starving in their frozen camp at Valley Forge, but was not finished until after the battles of Trenton, Princeton and Monmouth. At the last place, Washington suggested to the artist, himself a captain of volunteers in the Revolution, that he would find a good background for the picture in the view from the window of the farm-house where they were then sitting. Peale accordingly added Monmouth Court House and a party of Hessians leaving it under guard of the American troops. Old Nassau College at Princeton, where the picture was finished, also appears.
This painting was ordered by a resolution of the Continental Congress. That body adjourned, however, without making the appropriation for its purchase. A replica was executed, under a commission from Lafayette, for Louis XVI., which is now at Versailles. The original painting in the Capitol also was sent to France, where it seems to have been sold at public sale, but not for the benefit of the artist. It became the property of Count de Menou, perhaps under the delusion that it was the court picture. He brought it to America when he was charge" d'affaires at Washington, and placed it in the National Institute. When that association dissolved, the painting, with the other treasures then deposited in the Patent Office, found a home in the Smithsonian Institution. In 1876, it was temporarily hung in the Philadelphia Academy of Fine Arts, and, later, in the Corcoran Art Gallery. The Peale family were always tenacious of their claim of ownership; and, as the Regents of the Smithsonian could find no record to the contrary, the picture was conceded to have been left with the National Institute by Count de Menou merely for safe keeping. The Joint Committee on the Library, finally being convinced of its authenticity and of title in the heirs of Peale, purchased it in 1882 of Titian Ramsay Peale, son of the artist and assignee of the estate of Charles B. Calvert, for $5,000.