Bauhaus-Universität Weimar

109 
Some new apparatics. 
Volt reducers. 
When the city current is at hand in the laboratory, it is very desir¬ 
able to use it for forks, spark coils, telegraph keys, etc. This cannot 
be conveniently done on account of the high voltage of the current 
which arcs across the keys, burns out the platinum contacts, etc. 
With a battery current Helmholtz1 used a zigzag of resistance wire 
connected in parallel with the cup of the tuning fork in which he 
wished to suppress the spark. This idea has been developed by our 
laboratory mechanician, J. J. Hogan, into an arrangement by which 
the dynamo current of high voltage can be manipulated just as a 
number of galvanic cells. With the cells the current is altered in 
potential and intensity by the use of more or less of them and by 
their arrangement in parallel, in series or in combination. With the 
volt reducer the amount of current drawn from the dynamo is regu¬ 
lated by incandescent lamps. This current passes to a pair of bind¬ 
ing-posts by way of the apparatus in which the current is desired, 
and by way of one or more coils of wire. The particular arrange¬ 
ment of the coils depends on the insertion of various plugs. In this 
way the current drawn from the binding-posts can be made of any 
potential from 1 volt to 10 volts and of any intensity within the 
limits of the particular volt-reducer. The current acts under vary¬ 
ing circumstances exactly like that of a battery of the same potential 
and internal resistance. 
! Helmholtz, Die Lehre von d. Tonempfindungen, 632, 3 ed., Braunschweig, I87t.
        

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