Barker's Civil War diary contains a unique record of the events leading up to the fall of Richmond. It is written, interestingly enough, in a ledger book taken from the Confederate Provost Marshal's office in Fredericksburg when the 40th Massachusetts occupied that town. The first six pages of the ledger contain brief medical records (little more than notes) on Confederate soldiers, apparently kept by a Confederate surgeon at Fredericksburg in February, 1865.
As a Chaplain, drawing comparatively high pay and being freed from many of the routine duties of other soldiers, Barker had far more opportunities to observe the area around Richmond and to visit different parts of Richmond than the average soldier. Barker's curiosity led him to visit several of the better-known sights, including Chimborazo Hospital, Hollywood Cemetery, the prison, and the area of town where the "F.F.V.'s" lived. Most interestingly, he often took the opportunity to speak with local inhabitants, both Union sympathizers and die-hard Confederates, other clergymen, and physicians. Barker writes clearly, intelligently, and with insight about the end of the war, and he provides vivid accounts of the first days of Union occupation in Richmond. The diary also includes a particularly valuable account of Fredericksburg when occupied by Union forces in February, 1865.
The diary that Barker kept during his passage from England to America in 1855 contains daily accounts of his activities from the first of the year through the time of his sea voyage and arrival in Monson. A few entries, most notably those at the beginning of the diary, during the days surrounding his departure, and those written immediately preceding and upon his arrival in Boston are very full, and contain unusually detailed accounts of the emotions and experiences of a young man emigrating to America for economic betterment, who is forced, albeit temporarily, to leave most of his family behind. Like his Civil War diary, it is marked with intelligent, though occasionally overly moralistic observations. Included at the end of the diary are 18 poems written by Barker during the voyage on various topics, including freedom in a slave-holding society, the ocean, his family, and emigration.