US Presidents Trivia: Who was the only President to "affirm," not "swear" at his inaugural?

The Presidential oath is prescribed in the U.S. Constitution and reads as follows:  I do solemnly swear (or affirm) that I will faithfully execute the Office of President of the United States, and will to the best of my ability, preserve, protect and defend the Constitution of the United States.  The words are relatively ingrained on the consciousness of the American public and images of President's taking the oath are broadcast across the world.  Only one President in American history "affirmed," rather than swore, the oath.  Off of Pocket Trivia: US Presidents - US Presidents Trivia: Who was the only President to "affirm," not "swear" at his inaugural?  Was it Thomas Jefferson, Bill Clinton, Franklin Pierce or William Taft?



The correct answer to this one is Franklin Pierce, and the reasoning is very, very sad.

After Pierce's election but before he was sworn in, Pierce and his family were riding in a train near Boston.  The train derailed and rolled down an embankment.  Pierce and his wife, Jane, were unharmed, but their 11 year old son was crushed.  As a result, Pierce lost his faith in God.  He became the first (and thus far, only) President to affirm the Presidential oath, rather than swear.  He also placed his hand on a law book, not the Bible.