| The Jolly balance is used today in experiments on Hooke's
law and the period of a spring, and on surface tension. In both cases a
light spring is mounted from the arm that projects from the top of the
apparatus. The arm is mounted on a slider that can be cranked up and down.
The bottom of the spring is located accurately by observing it in the (mirrored)
scale let into the front of the balance.
The spring constant is found using a static technique by hanging progressively larger masses on the end of the scale. Or, it can be found by using a series of masses and measuring the period of oscillation of the system.
The Jolly balance is used with the spring to supply a calibrated force to pull a clean platinum ring out of the surface of liquid held in a small container on the shelf. The top of the spring is raised with the slider until the ring lets loose from the water.
Phillipp Gustav von Jolly (1809-1884) invented the balance about 1874. He was a professor at the University of Munich, where he encouraged his students to do experimental work in his laboratory.