Induction Coil (Phipps and Bird, Inc., 1925)

Primary coil connected to ordinary galvanic battery. When switch closes to permit current to flow in primary coil, an impulse is generated in 2nd coil. As current continues flowing in the primary, nothing more happens in the secondary, until current in the primary is interrupted. A 2nd impulse is then generated in the secondary. 2 impulses in secondary are not identical & therefore designated as "make" & "break" impulses, respectively. (Donated by K. Schmidt-Nielsen, Duke University)