. Elementary and dental radiography / by Howard Riley Raper . lts, between lit and 1>. happen if the core were wound with uninsulated wire. If this were donethe current would not follow the windings of the wire at all, but wouldchoose the shorter path of less resistance, passing along the iron core,making a short circuit.) Over the primary winding is placed a heavyinsulation of mica or vulcanite, and around this is wound more insulatedwire, the secondary winding. (Figs. 32 and 33.) There is positively no electric connection between the primary andsecondary windings. The primary current pass
. Elementary and dental radiography / by Howard Riley Raper . lts, between lit and 1>. happen if the core were wound with uninsulated wire. If this were donethe current would not follow the windings of the wire at all, but wouldchoose the shorter path of less resistance, passing along the iron core,making a short circuit.) Over the primary winding is placed a heavyinsulation of mica or vulcanite, and around this is wound more insulatedwire, the secondary winding. (Figs. 32 and 33.) There is positively no electric connection between the primary andsecondary windings. The primary current passes through the primary 28 ELEMENTARY RADIOGRAPHY winding and into the negative lead wire. But in its passage it has in-duced or created a secondary current in the secondary winding. Coils are rated and designated according to the maximum num-ber of inches of atmosphere the secondary current can be made to the current jumps from one terminal to the other of the secondarywinding, a spark occurs, due to the resistance of the atmosphere to the Y ,.E D B. Fig. 25. Fig. 26. Fig. 25. A, movable arm with fulcrum at B. C, electro-magnet. D, break. E, 2fi. A, piece of ribbon steel. B, point where circuit is broken. (, electro-magnet. flow of the current. When we speak of a coil as, say a 12-inch coil, wemean that the spark gap of that coil is twelve inches long; that its sec-ondary current can be made to jump twelve inches of atmosphere. Coilswith parallel spark gaps from as narrow as about 6 inches to as long asabout 40 inches have been manufactured. The induction coils manufactured today usually have a spark gapof from 8 to 12 inches. (See pages 43 and 44.) The wire of the primary winding is from about 16- to 4-gauge; ofthe secondary from about 34- to 29-gauge. The length of the wire in thesecondary is immensely greater than the length of the wire in the primary. X-RAY MACHINES 29
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