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INDUCTION COILS 215
Photographing an Electric Discharge

The following experiment must be conducted in a dark
room with the aid of a ruby photographic lamp, as other-
wise the plates used would become lightsch and
spoiled.

Placed an ordinary photographic plate on a piece of sheet-
metal with the coated side of the plate upwards. Connect

  
     
  
    

JECONDAR Y

TERMINAL \

SEC ONDA Rr
/ Tt'RMINAL

 

 

FIG. I71. — Jacob’s Ladder.

one of the secondary terminals of the spark-coil to the piece
of sheet-metal.

Then sift a thin film of dry starch powder, sulphur, or
talcum through a piece of fine gauze on the plate. Lead a
sharp-pointed wire from the other secondary terminal of
the coil to the center of the plate and then push the key
just long enough to make one spark.

Wipe the powder 03 the plate and develop it in the usual
manner of films and plates. [If you cannot do developing

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