APPARATUS 



77 



method of vibrations, much smaller differences can be recog- 

 nised. The only change in the construction of chemical balances 

 which has become general within the last thirty years, is the 

 shortening of the beam, in consequence of which its oscillations 

 are quicker, and therefore the business of weighing is abbreviated. 



The ordinary balance agrees in principle with the common 

 systems of scales and weights. The accompanying illustration 

 shows an ordinary short 

 beam balance of modern 

 type. It consists of a 

 two-armed lever, the 

 centre point of which is 

 suspended on a knife edge 

 which rests on a plane 

 surface of agate. The 

 pans are also suspended 

 on knife edges resting on 

 agate planes when the 

 balance is in use. When 

 not actually in operation 

 the beam and the pan 

 supports are raised from 

 contact with the planes. 

 This is accomplished by 

 turning the screw head 

 in the middle of the box 

 below. The divided scale 

 above the beam carries 



a small rider of wire, the position of which can be altered, and 

 the final adjustment of weight effected. The chemist's balance 

 differs from the pillar scales of the grocer or druggist only in 

 superiority of workmanship and materials whereby it is made 

 vastly more accurate and sensitive. 



The balance about to be described differs in principle from all 

 ordinary balances, and in the skilled hands of the inventors and 

 others exhibits a degree of sensitiveness and delicacy in dealing 

 with small masses which has hitherto been unheard of. It is 

 obviously applicable only to exceptional cases. 



The new balance is described by the inventors, Professor 

 B. D. Steele and Mr. Kerr Grant, in the Proceedings of the 

 Royal Society for 1909, and in addition to the interest attaching 



FIG. 38. A SHORT BEAM BALANCE. 



