|Newton's Third Law of Motion|
|Inventor||Sir Isaac Newton|
|First Appearance||"The Knockdown"|
"To every action there is always an equal and opposite reaction: or the forces of two bodies on each other are always equal and are directed in opposite directions."
Newton's Third Law of Motion was used by Detective William Murdoch while he was investigating the murder of the boxer Amos Robinson. Murdoch asserted that he knew Fannie Robinson was innocent because she did not have the proper blood splatter on her clothing. Had she shot her husband the "equal and opposite reaction" would have been for blood to splatter her. Murdoch later demonstrated this principle by having Constable George Crabtree shoot a gun at a deceased pig ("The Knockdown").