The ampere-turns in a primary circuit of an induction coil or
transformer. In an electric welding transformer, or in the transformer
used in the alternating current system, where efficiency is an important
element, the ampere-turns in primary and secondary for an efficiency of
100 per cent. should be equal. In the case of an experimental induction
coil other considerations outweigh that of mere efficiency. Insulation,
including security from piercing, and the production of as long a spark
as possible, are, in these cases, the controlling consideration.

[Transcriber's note: A 100 per cent efficient transformer is impossible,
but over 99 per cent is common. At room temperature there is always some
lost flux, eddy currents and resistive losses.]