GENERAL PHYSIOLOGY OF MUSCLE AND NERVE TISSUE 43 



other apparatus, which should be arranged as shown in Fig. 20. 

 Repeat the observations on the angle of deviation of the needle using 

 the ohm, 10 ohms, and 100 ohms resistance as above. 



(6) Join up four cells tandem or in series, and repeat the three 

 observations. 



(7) Join up six cells in series and repeat observations. 



(8) Tabulate results and draw conclusions: 



1. There is a marked difference in the results of the two methods. 



2. With low external or circuit resistance the current is indicated 

 by the angle at which the galvanoscope needle stood increased with 

 an increase in the number of cells joined multiple arc or abreast. 



FIG. 22 



3. With high external resistance the strength of the current does 

 not seem to be essentially increased by increasing the number of 

 cells joined up abreast. 



4. With low external resistance the strength of the current is not 

 increased by adding cells in series. 



5. With high external resistance the strength of current increases 

 with an increase in the number of cells joined up in series or tandem. 



IX. METHODS OF VARYING THE STRENGTH OF CURRENT. 



It has already been shown that the strength of current may be 

 varied by increasing the number of cells or by changing their arrange- 

 ment in the battery. This method is indispensable, but it has its 

 limitations. If one has a small cell and wishes to decrease the current, 

 he must have a recourse to another method. 



E 



From the formula C=^ it is evident that one may decrease the 

 R 



current by increasing the resistance. 



(a) The Rheostat. 



1. Appliances. Resistance box or rheostat; 1 cell; 5 wires; 

 galvanoscope or galvanometer. 



2. Experiments and Observations. (I) Set up the apparatus as 

 shown in Fig. 20. 



