E. H. Kraus — A New Jolly Balance. 561 



Art. XL VII. — A New Jolly Balance', by Edward H. Kraus. 



The first important modification of the spiral spring balance, 

 devised by Jolly, was introduced by Linebarger* in 1900, 

 whose improved balance has since been used rather extensively. 

 The balance to be described has several new features, of which 

 the recording of the elongations of the spiral spring and the 

 reducing of the number of readings necessary to determine 

 the specific gravity are the most important. 



The balance consists of the square upright tube T to which 

 the fixed vernier M and the movable graduated scale X are 

 attached, as shown in the accompanying figure. A second 

 tube Z is movable within T by means of the miiled-head A. 

 The movable vernier N is attached to Z by the arm E. The 

 screw B controls the rod R, movable within the tube Z. From 

 R the spiral spring S and scale pans C and D are suspended, 

 the thin wire rods W and V connecting the spring and scale 

 pans with the pointer P, which swings freely in front of a 

 small circular mirror. 



In using the balance for the determination of the specific 

 gravity of a solid, for example a mineral, it is necessary that 

 the graduated scale X, the verniers M and N, and the pointer 

 P all be at zero, the lower scale pan being immersed in water. 

 Since the vernier M is fixed, the zero positions of N and X 

 will be opposite M. The pointer P is brought to zero by 

 being made to coincide with the index on the small circular 

 mirror, the adjustment being accomplished by the screw B. 

 A fragment is now placed on the upper pan C and the elonga- 

 tion of the spring determined by again bringing the pointer P to 

 the zero position. This is now done by turning the mill-head 

 A, which moves the tube Z, the graduated scale X and the 

 vernier N, upward. After the zero position of the pointer is 

 obtained, the scale X is clamped by the screw Y. It is 

 obvious that the reading at M will give directly the elongation 

 of the spring due to the weight of the specimen in air. The 

 fragment is now transferred to the pan I) under water. The 

 pointer P is again, for the third time, brought to zero ; this 

 time by moving the tube Z and the vernier N downward by 

 means of A, the scale X remaining fixed, having been clamped 

 by the screw Y. The reading at N gives at once the loss in 

 the elongation due to the immersion of the fragment in water. 

 Hence, if the weight in air be represented by "W, the read- 

 ing at M, and the loss of weight when immersed in water by 



* Physical Eeview, xi, 110-111, 1900. 



