Jolly's Balance

Instrument for determining the specific gravity of small solids. It consists of a vertical spiral spring, at the lower end of which are suspended two scale pans. The lower one is always immersed in water, and is attached to the bottom of the upper one by a fine thread or wire. Just behind the pans is a vertical millimeter scale, etched on mirror gla , from which can be read the position of an index mark fixed on the suspending wire just above the upper pan. The solid is placed in the upper pan and the position of the index noted. The body is then replaced by standard weights till the index stands at the same scale division as before. If this weight be W, it repre Jolly's Balance. 18, 1812.