xxvm.] 



SHOCKS AND CURRENTS. 



171 



LESSON XXVIII. 



SINGLE INDUCTION SHOCKS — INTERRUPTED 

 CURRENT—BREAK EXTRA-CURRENT — HELM- 

 HOLTZ'S MODIFICATION. 



1. Single Induction Shocks. — Apparatus.— Daniell's cell, in- 

 duction machine, wires, two Du Bois keys (or one Du Bois and 

 one spring or mercury key), and electrodes. 



(a.) Make connections as in fig, 99. The key in the primary 

 circuit — preferably a mercury key — is used to make or break the 

 primary current. To the binding screws of the secondary coil 

 attach two wires, and connect them to the short-circuiting Du 

 Bois key, and to the latter the electrodes. 



Fia. 99.— Scheme for Single Induction Shocks. B. Battery ; K, K'. Keys ; P. Primary, 

 and S. Secondary coil of the induction machine ; N. Nerve ; M. Muscle. 



(b.) Effect on Tongue of Single Induction Shocks.— Open the 



short-circuiting key, push the secondary coil pretty near to the 

 primary, and place the points of the electrodes on the tip of the 

 tongue, or hold them between the forefinger and thumb moistened 

 with water. Close the key in the primary circuit, i.e., make the 

 circuit, and instantaneously at the moment of making, a shock or 

 prick — the closing or make induction shock — is induced in the 

 secondary coil, S, and is felt on the tip of the tongue or finger. 

 All the time the key. is closed the galvanic current is circulating in 

 the primary coil, but it is only when the primary current is made 

 or broken that a shock is induced in the secondary coil. 



(c.) Break the primary current by raising the key, and instan- 

 taneously a shock — the opening or break induction shock — is felt. 



(d.) The break is stronger titan the male shod-. Push the 

 secondary coil a long distance from the primary, and, while the 

 electrodes are on the tongue, make and break the primary circuit. 

 Gradually move the secondary near the primary coil. The break 

 shock is felt first, and on pushing the secondary nearer the primary 



