EXPERIMENT STATION BULLETINS. 



581 



rent on the bridge by adjusting the variable resistance until a maxi- 

 mum sensibility is obtained. At the same time adjust the condenser to 

 balance out the capacity of the cup. Carefully adjust all three, the cur- 

 rent, the resistance and the condenser and make a careful reading. Make 

 another filling of the cell and repeat operations until checks are obtained. 



5. EXPERIMENTAL. 



The apparatus we have assembled is not only less tedious or trying to 

 operate but shows a high degree of precision. We note below the data on 

 a few experiments. It is not necessary at this time to publish at further 

 length, for in this paper we wish only to describe the apparatus and its 

 method of operation and draw attention to its applicability to biological 

 problems and reserve for a future publication the experiments for which 

 this apparatus was primarily devised. 



Experiment I. 



The object of this experiment is to show the precision that can be ob- 

 tained when using certain values of known resistances, balanced against 

 each other. The new Curtis Coils were used. In the table below one set 

 of coils is designated as A and the other as B. The "perfect balance" is 

 defined as that point at which the galvanometer scale does not move. Now 

 if the bridge is moved .1 of a scale division either side of this point, a 

 deflection of the galvanometer is seen. A tenth of a scale division is 

 selected, as this is about the smallest deviation which can be estimated 

 without the use of a micrometer screw, and magnifying glass. The 

 "extended" E and "short" S bridge wires were used. The former is used 

 when an accuracy of more than .05 per cent is desired. The latter is suffi- 

 cient for all tests of culture solution. 



GALVANOMETER METHOD. 



