How does Maxwell explain the toroid experiment in "On Physical Lines of Force"? In Maxwell's paper "On Physical Lines of Force", Part II, he describes an experiment with a toroid (B) and a circuit (C). Here is his drawing:

He says a current in B will induce a current in C. How does Maxwell explain this using his rotating vortecies? I do not find his explanation very clear, nor could I find any explanation online.
This is my reasoning so far: If there was no circuit C, then there would be no magnetic field outside B because it is canceled. Is the presence of the circuit C making the cancelation if the magnetic field to act differently and thereby induce a current?
Edit:
What I meant to say was "He says a varying current in B will induce a current in C."
How does Maxwell explain this using his rotating vortecies?
 A: Maxwell does not say that a current in B will induce a current in C, and you are right that ideally it doesn't. He says (according to Wikisource, emphasis mine):

an electromotive force will act on that wire [C] whenever the current in the coil [B] is made to vary

and it should be clear why (in the modern understanding). When there's a current in B, there's a magnetic field set up inside the coil whose strength depends on the current, even though there is ideally none outside. Though the wire C is in that region of no magnetic field, any surface with boundary C will pass through the interior of the torus, where there is a magnetic field. Changing the current in B would change the magnetic flux through that surface, therefore inducing EMFs along C in such a way that the resulting current in C and its induced magnetic field try to counter the change in the field inside the torus.
As to how he explains it with his vortices, I believe the way to think about it is this: When there's current through B, Maxwell's "particles" are in motion in the direction of the current. The particles move by rolling without slipping against the vortices of the magnetic "fluid", and therefore their motion sets up vortices (a magnetic field) inside the torus. Note that the vortices must rotate the opposite way as the particles. The magnetic field also happens to cancel outside the torus. If you halt the current, then the particles can no longer move, but can still rotate in place. Rotate they must, because the magnetic vortices are still there and they transfer their motion to the particles (which rotate the opposite way as the vortices). The particles then transfer that motion to the surrounding magnetic vortices (which now rotate the same way as the first vortices), which transfer it further, etc. This time the fields don't cancel and you get a radiating EM pulse that induces a current in C once it reaches it. The pulse does not induce currents in the air because the resistance of the air is too high, so energy is transmitted only through the rotations of particles and vortices in place. (Maxwell conceives of resistance as the resistance to particles moving between vortices.) The wire is much more conductive, so the particles can get a current started in the moment between the magnetic vortices just on the inside of the loop starting to rotate and exert a force on the particles and the moment the vortices on the outside start rotating and cancel the EMF.
Note that this example is just a more complicated version of the one in the section before, which is about figure 2. I believe the intention was that fig. 2 would be sufficient to explain how changing magnetic fields can induce current (and specifically that a change in current induces currents opposing the change), and then fig. 3 is an example where the cancellation has been chosen to make the magnetic field zero at the position of the induced current.
