31. In RF induction plasma torches, energy coupling to the plasma is accomplished through the electromagnetic field generated by the induction coil . 32. Another disadvantage is that the induction coils must be custom built for each molding because the coils must be from the part. 33. Instrument-makers in America, Great Britain and the European continent contributed in developing the construction and operation of induction coils . 34. Although Ruhmkorff is often credited with the invention of the induction coil , it was in fact invented by Nicholas Callan in 1836. 35. In traverse hardening systems the work piece is passed through the induction coil progressively and a following quench spray or ring is utilised. 36. Starting in the 1930s, the base of the telephone also enclosed its bell and induction coil , obviating a separate ringer box. 37. The induction coil is a fly-back system, using interruption of electrical primary system current through some type of synchronized interrupter. 38. He built a thirteen-inch ( 33 cm ) induction coil , sponsored by local individuals and this permitted shorter exposure times. 39. The batteries are periodically charged through non-contact charging using induction coils in the ground where the cars rest at Sunset Boulevard stop. 40. In the 1930s, telephone sets were developed that combined the bell and induction coil with the desk set, obviating a separate ringer box.
