Equal-arm balances were such common laboratory appliances that we were rarely aware of them Now that we have electronic balances for routine measurements, the  balances on this pages are beginning to disappear. The equal arm balance at the right has a hook on one side, indicating that it was could also be used for specific gravity measurements. 

   This apparatus, which was at Wittenberg University when I photographed it in 1979, was purchased from the firm of James W. Queen of Philadelphia. The description in 1881 catalogue reads "Balance for Specific Gravity, and other purposes. Arm of brass, ten inches long, supported on knife edge. Pans of brass. Support of brass on wooden base 12.00"

   This platform (or Roberval) balance is at Virginia Military Academy, and has "A. P. Gage & Son, Boston" hand-lettered on the side. 

   Gage was the instructor in physics at the English High School in Boston. In 1882 he published his "Elements of Physics" for students in high schools and academies. In the Preface to the book, he noted that the sum of $300 was sufficient to set up a laboratory program in physics for a large school. 

   The scale at the right was made by John Millington about 1840 when he was teaching at the College of William and Mary. It is presently at the University Museum at the University of Mississippi, where Millington was the first professor of natural philosophy in the years 1848 to 1853. 

   An earlier picture of the balance (W.L.Kennon and S.C. Gladden, "Historical Apparatus at the University of Mississippi", The American Physics Teacher, 6, 1-7 (1938), shows that it has suffered some damage. Originally it had an L-shaped structure swinging on a pivot through the hole in the top of the upright pillar. One arm extended to the left, with a hanging pan suspended from it. The other arm carried the pointer and a counterweight, making the scale look like a large-scale version of a modern postal scale. 

  This small pair of gold scales is in the Greenslade Collection. I found the weights in the box to be as interesting, as they are marked with six dots, five dots, .. one dot. After a bit of experimenting with an electronic balance, I discovered that the six dot weight was a six drachm (or dram) weight; today drams are used by pharmacists, but not by physicists. One dram is 3.889 grams or 60 grains. 
   This glass-enclosed Torsion Balance uses a twisted strip of steel to provide a restoring force. It is by the Torsion Balance Company of New York, is probably from the 1930s and is in the Greenslade Collection.

This is a large picture of a small balance. It is about 25 cm in length, and is marked off in grains. Unlike most balances, it has adjustable weights on either side of the pivot point. On the right-hand side, the scale runs from 0 to 400 grains, with the zero point closer to the pivot. The left-hand scale, running from 0 to 30 grains, has its zero point close to the pan holding the unknown. The instrument was given to the Greenslade Collection by Daniel Chaucer.


   The small balance at the left was made by H.L. Becker's Sons & Company of Brussels and Den Haag. It is only 32 cm high.

   It can be found in the Greenslade Collection.

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