early 20th century american industrial type "h" closed core bench top transformer designed and fabricated by or for the edgcomb & pyle wireless co., pittsburgh, pa. the transformer's coils are enclosed within the original varnished oak wood cabinet with beveled edges. a transformer is a power converter that transfers electrical energy from one circuit to another through the transformer's coils. a varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary winding. this varying magnetic field induces a varying electromotive force (emf), or "voltage", in the secondary winding. if a load is connected to the secondary winding, current will flow in this winding, and electrical energy will be transferred from the primary circuit through the transformer to the load. in the autumn of 1884, károly zipernowsky, ottó bláthy and miksa déri (z.b.d.), three engineers associated with the ganz factory, had determined that open-core devices were impracticable, as they were incapable of reliably regulating voltage. in their joint 1885 patent applications for novel transformers (later called z.b.d. transformers), they described two designs with closed magnetic circuits where copper windings were either a) wound around iron wire ring core or b) surrounded by iron wire core. the two designs were the first application of the two basic transformer construction types in common use to this day which can as a class all be termed as either core form or shell form. their patents included two major interrelated innovations: one concerning the use of parallel connected, instead of series connected, utilization loads, the other concerning the ability to have high turns ratio transformers such that the supply network voltage could be much higher (initially 1,400 to 2,000 v) than the voltage of utilization loads (100 v initially preferred). when they employed them in parallel connected electric distribution systems, closed-core transformers finally made it technically and economically feasible to provide electric power for lighting in homes, businesses and public spaces. bláthy had suggested the use of closed-cores, zipernowsky the use of parallel shunt connections, and déri had performed the experiments; transformers in use today are designed based on principles discovered by the three engineers. they also popularized the word "transformer" to describe a device for altering the emf of an electric current, although the term had already been in use by 1882.[25][26] in 1886, the z.b.d. engineers designed, and the ganz factory supplied electrical equipment for, the world's first power station that used ac generators to power a parallel connected common electrical network, the steam-powered rome-cerchi power plant. measures 9 1/2 x 9 1/2 x 7 inches.