Bridges I have crossed

The Wheatstone bridge was still in use when I received my Ph.D. in physics in the early 1960s. I researched the thermal conductivity of superconducting thin films at Rutgers University in New Jersey using standard 1/10 W Allen-Bradley carbon resistors as thermometers and measured their resistance with a Wheatstone bridge built from top-of-the line components. Since then, I have moved from experimental physics to the study of apparatus used in physics in the late 19th and early 20th centuries. During this time, the construction of high-precision electrical measurement equipment was raised to an art in the United States by companies such as Leeds & Northrup (L&N) of Philadelphia and General Radio Co. of Cambridge, Massachusetts. In this paper I will discuss some favorite pieces of apparatus in my own collection based on bridge circuits.