226 



ELECTRIC EFFECTS. 



electricity ; it is burred on both sides. The phenomena of attraction 

 and repulsion, already made familiar, come under this head. 



370. Physiological Effects. The "electric 

 shock," which is physiological in its nature, is familiar to 

 most persons. The sensation thus produced cannot be 

 described, forgotten or produced by any other agency. It 

 has been found an efficient agent in medical practice. 

 Such experiments, however, should be performed with 

 caution. 



(a.) If the members of a class form a chain by joining hands, the 

 first member holding a feebly-charged Leyden jar by its outer coat, 

 and the last member touching the knob, a simultaneous shock will 

 be felt by each person in the chain. A single Leyden jar has thus 

 been discharged through a regiment of 1500 men, each soldier 

 receiving a shock. Dr. Priestley killed a rat with a battery of seven 

 feet of coated surface, and a cat with a battery of forty feet of 

 coated surface. 



371. Apparatus and Experiments. It is not 



necessary nor very desirable that all of the 

 following experiments be performed. Several 

 of them involve the same principle ; but one 

 teacher may have one piece of apparatus and 

 another, another piece. 



FIG. 161. 



(1.) Fig. 161 repre- 

 sents the "electric 

 bells." The metal 

 frame is hung from 

 the prime conductor. The right-hand 

 bell is suspended by a wire ; the other 

 bell is suspended by a silk cord and 

 connected with the ground by means 

 of a chain hanging on the floor. When 

 the machine is worked slowly, the 

 clapper vibrates and rings the bells. 

 Explain. 



(2.) In the "electric chime," repre- 

 sented in Fig. 162, the outer bells 



FIG. 162. 



