Well there are some possibilities with modifications to two windings. the way it showed on the schematic though was they were jsut hooked in parallel. I just tried hooking two solenoids end to end and connected a diode between them and energized the front one in hopes that when I turned the front one off the collapsing field would go through the diode to energize the second coil and pull the rod into the second coil. didnt seem to work that way.

The other possibliity is that he wound the second coil the opposite direction to the first. I dont hear anybody talking about that ever. There is a left handed coil and a right handed coil so I wonder what happens when you wind them both on the same core and hook them in parallel. the polarity of the magnetic field does not change its still goes the same direction. but I wonder if it affects the magnetic flux any.

But when you wind a coil going back and forth from end to end you are creating both left and right handed coils. I wonder if this is where back EMF comes from. maybe if one winds a coil so it is only right hand or left hand something would change. It wolud be hard to do however as it wolud end up being a series of pancake coils stacked together and hooked in series. but might be worth a try. pancake coils are intresting becaues they are not left hatd or right hand becaues you can just flip them over to reverse them. with a long coil you cant do that as they are mirror images of each other. You can prove that by winding a couple of coil from a few inches of wire.

So other possibilites are that if one could open the circuit of just one of the coils and then switch it to a different circuit it would hook the two coils in series and the collapse of the field would then be going through double the length of wire. kind of like switching the setup from parallel to series suddenly.

Anywway thats enough of the speculation on my part.