In our Dublin, New Hampshire, office hangs a reproduction of a painting by Norman Rockwell depicting Abraham Lincoln standing in front of a jury holding the 1857 edition of an almanac in his hand. Was it The Old Farmer's Almanac?
It's difficult to prove conclusively, but everything I've read about the case—and certainly my examination of the 1857 edition—indicates that it was.
The occasion depicted in the Rockwell painting is the 1858 murder trial of an Illinois man named William "Duff" Armstrong. Armstrong was accused of murdering James Preston Metzker with a "slung-shot"—a weight tied to a leather thong, sort of an early blackjack—a few minutes before midnight of August 29, 1857. Lincoln was a friend of the accused man's father, Jack Armstrong, who'd just died, and so he offered to help defend young Duff Armstrong, without pay, as a favor to Jack Armstrong's widow.
The principal prosecution witness against Armstrong was a man named Charles Allen, who testified that he'd seen the murder from about 150 feet away. When Lincoln asked Allen how he could tell it was Armstrong given that it was the middle of the night and he was a considerable distance away from the murder scene, Allen replied, "By the light of the Moon."
Enter the Almanac!
Upon hearing Allen's testimony, Lincoln produced a copy of the 1857 edition, turned to the two calendar pages for August, and showed the jury that not only was the moon in the first quarter but it was riding "low" on the horizon, about to set, at the precise time of the murder. There would not have been enough light for Allen to identify Armstrong or anyone else, said Lincoln. The jury agreed, and Duff Armstrong was acquitted.