36 LABORATORY GUIDE IN PHYSIOLOGY. 



plate uncoupled. These two uncoupled terminal 

 plates of the battery are the ones from which to 

 lead off the wires to the other apparatus, which 

 should be arranged as shown in PI. I., Fig. 6. 

 Repeat the observations on the angle of deviation 

 of the needle, using the QO, 10.Q and 100.Q 

 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 

 as indicated by the angle at which the detector needle stood 

 increased with an increase in the number of cells joined in 

 multiple arc or abreast. 



3. With high external resistance the strength of the 

 current does not seem to be essentially increased by in- 

 creasing 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. 



The following theoretical points are worthy of note : 

 The general formula C=g does not differentiate le 

 tween that part of the resistance furnished by the battery 

 and that part furnished by the external circuit. The 

 former is called internal resistance (ri) and the latter is 

 called external resistance (re). So we may write 



