Patients often sat in chairs for the treatments placed on metal grounding plates that were attatched to the bottom of the coil. The top of the coil was attatched to a large circular plate with many needles that was placed a foot or so from the patients body - causing the body to act as a sort of dielectric with the electodes. The effluve is rich in ultra-violet radiation. The effluve is comparable to a spark being transformed into a mist of 1000 sparks. A high frequency coil of relatively few turns using thick wire.
Treatments are always bi-polar.
Think of a d'Arsonval coil as an Oudin Resonator without a secondary coil. Thermo-Penetration a vague term for bipolar treatments of either the d'arsonval or diathermic types. With diathermy coils this could have been as low as 1200 volts. The current is low for d'Arsonval coils and very high for diathermy coils. Treatment times varied from apparatus to apparatus because of these factors.