ABSTRACT
Until the late 1920s a spark coil was an essential piece of apparatus for all except a few of the earliest X-ray experimentalists who, as an alternative, used electrostatic machines such as the Wimshurst, which were generally unreliable. If the terminals are separated so the spark will not jump the gap, the induced current will be available in the Crookes Tube for the production of X-rays.' X-ray units would be wanted for the Forces and 10" and 12" spark coils crackled away on the test benches, whilst the writer was engaged in the delectable task of cleaning mercury 'breaks' or interrupters, surely the dirtiest and most smelly job in the whole of Christendom. Mercury interrupters and spark coils were eventually superseded for the production of high tension by transformers in which the laminated iron core formed a closed loop, and was not a straight core as in the spark coils.
