MUSCLE-NERVE. 



1. Place the primary inside of the secondary. By means of a 

 key interposed in the primary circuit (a) make the current. Is 

 there any movement of the galvanometer needle ? What is the di- 

 rection and degree of this movement ? (b) Break the primary cir- 

 cuit. What is the movement of the galvanometer needle? Does 

 the needle remain in the position which it assumes upon either the 

 make or break of the primary circuit? (c) Repeat (a) and (b), 

 moving the primary farther and farther from the secondary. Is 

 there any difference in the excursion of the galvanometer needle ? 

 Is there any difference in the degree of excursion of the needle at 

 make, as compared with break of the primary circuit ? 



2. (a) With the key of the primary circuit closed, suddenly 

 withdraw the primary coil from the secondary. What is the effect 

 on the position of the galvanometer needle? (b) Now suddenly 

 approach the primary toward the secondary and note the effect on 

 the galvanometer. 



3. (a) With the primary placed to one side, introduce a per- 

 manent magnet rod into the secondary. What is the effect on 

 the galvanometer? (b) Withdraw the magnet. What is the re- 

 sult? 



4. With a simple rheocord in the primary circuit, suddenly in- 

 crease or decrease the resistance by quickly moving the slider back 

 and forth. Is any current induced in the secondary through 

 changing the intensity of the primary current ? 



5. Apply the electrodes from the secondary coil of an inducto- 

 rium to the tip of your tongue. Open and close the primary circuit 

 with the primary some distance removed from the secondary. Re- 

 peat, gradually moving the secondary toward the primary until 

 the shocks produced are too strong for comfort. Which shock is 

 first detected by the tongue? Why should the break shock be 

 stronger than the make ? What is the possibility of the production 

 of induced currents in the coils of the primary itself ? What would 

 be their effect on the make as compared with the break currents ? 

 These currents are known as make-extra and break-extra cur- 

 rents. 



