GENERAL PHYSIOLOGY. 35 



ohms, Allow the needle to come to rest and 

 note angle ? 



(V.) Remove from the rheostat plugs which will 

 represent in the aggregate 100 ohms of extra 

 resistance. Note angle of indicator as before. 

 (2) Join up two cells in multiple arc as shown in PL I., 

 Fig, 7. That is, join both copper plates to one 

 copper wire and both zinc plates to another. 

 These wires are to be carried to key, rheostat and 

 detector as shown in PI. I., Fig. 6. 

 (#.) Note angle of needle with no extra resistance. 

 (.) Note angle with 10 ohms extra resistance. 

 (V.) Note angle with 100 ohms extra resistance. 



FIG. 6. . 



FIG. 6. Detector, composed of simple magnetic needle mounted 

 over a graduated circle. The two heavy, copper wires which encircle 

 the compass offer slight resistance to the electric current. 



(3) Join up four cells in multiple arc or " abreast'' and 



repeat the observations of angle at the three re- 

 sistances as above. 



(4) Join up six cells in multiple arc and repeat observa- 



tions with 0/2, 10.Q, and 100/2 resistance. 



(5) Join up two cells in series as shown in PI. I., Fig. 



8. That is, join the copper of the first cell to the 

 zinc of the second. The first cell will have a zinc 

 uncoupled and the second will have a copper 



