torsion balance for gravitational experiment
Date: 1900-1930
Inventory Number: 1996-1-0178
Classification: Balance
Dimensions:45.5 x 28.5 x 25 cm (17 15/16 x 11 1/4 x 9 13/16 in.)
Accessories: leveling screw
DescriptionThe balance system is set in a wooden box with sliding plastic windows. The torsion beam is horizontal and finely rotates owing to a suspended wire (most likely a torsion fiber of quartz), which is enclosed in a vertical casing made of metal and glass. The beam carries at each end a 160 gram lead ball, called attracted masses. When the instrument is not in use, the beam and ball system is supported by small platforms positioned under the balls. The platforms move up and down. A small mirror is attached to the wire, and is seen from the round opening at the bottom of the casing.
The particularity of this instrument is that the torsion system was buoyed up by a copper float (a small circular plate) in a mercury bath, which is at the bottom of the box and made of glass. This particular type of system seems to be an original idea of G. K. Burgess, published in 1902. A vertical steel rod comes down from the horizontal beam's center of gravity, to which was attached the float completely immersed in the mercury. This float was used to calibrate the tension in the wire.
The Harvard number "ME12" is found on top of the box.