Late in July, 1777, the British general John Burgoyne found himself trapped by a colonial army in the upper reaches of the Hudson; he was about to lose the Battle of Saratoga. In desperation he wrote to Sir Henry Clinton in New York, asking for reinforcements. But the only available troops, under Sir William Howe, were off in Maryland. Clinton’s discouraging answer was a letter which had no apparent meaning until Burgoyne’s staff fitted a prearranged dumbbell-shaped mask over it. A replica of that letter and the superimposed mask (treated as if it were semitransparent) are shown below; they will soon appear in John Bakeless” Spies of the American Revolution , to be published by The J. B. Lippincott Company.