AT ONE POINT in his reporter's accounts of the Civil War, Walt Whitman described the wounded and dying Union soldiers as they lay in the makeshift hospital of the old U.S. Patent Office among the shiny new inventions - a stunning example of the two-sided mind of man. The old U.S. Patent Office is now the home of the National Portrait Gallery, where the living, not the killing, side of man has been on display 10 years today. One of the fascinations of the gallery is that it is not essentially a museum of art, though art is what it shows, much of it quite fine. Rather, the Portrait Gallery is a museum of life, or at least of history in its most active form.

The current daguerreotype show, "Facing the Light," is almost enough to justify a gallery in itself. Nothing so conveys the breadth of American history as the act of looking at a snapshot of Thomas Jefferson's secretary of the treasury. The question that follows from such an act, of course, is: What do you see? And in that question lies the deep uniqueness of the musuem. For what you see - in the deliberately vague self-portrait of Mary Cassatt, or in Emanuel Leutze's too pensive Hawthorne, or in Miriam Troop's too benign Richard Wright - is exactly what you get, meaning that the Portrait Gallery is specifically concerned with the element of appearance. You confront the photo of Thoreau who, in that photo, looks like the perfect snob of the simple life - was he really that? All you have in the gallery is one face at one time, and in that face must be read a whole life.

The Portrait Gallery is a place where faces consider faces.All that we think of ourselves or each other is on the walls of that remarkable institution - from the mad confidence of Eleazar Williams, an early 19th-century missionary who claimed to be the last Dauphin of France, to the facile arrogance of Issac Merritt Singer (the sewing machine Singer) decked out in ripe glory by Edward Harrison May. Singer, 6-feet-4 and round, in a gold and scarlet robe and a great white vest with a gold chain strung across it like a bridge. Singer, whose patents for the good life were on file in that same building where the Union soldiers lay.