Comprised of four arms, its namesake used it to measure resistance by comparing current flowing through one part with a known current flowing through another part.
Though this device was actually invented by Samuel Christie, it was popularized by its namesake.  The Pirani thermal conductivity gauge is basically one of these apparatuses with one part in the form of a heated filament placed in a vacuum system.  Comprised of four arms, its namesake used it to measure resistance by comparing current flowing through one part with a known current flowing through another part. FTP, identify this so-called "bridge."
Though this device was actually invented by Samuel Christie, it was popularized by its namesake.  
Wheatstone bridge (only need the name after the end of the question)