Here the agate block attached to the pendulum, which is swinging to the left, has just made contact with the little toggle that is hanging down from the lower contact. As the pendulum continues onwards to the left, the toggle will now start to slide up the surface of the agate block as can be seen below.

Here the toggle can clearly be seen starting to slide up the curved face of the agate block.

The pendulum has continued further to the left, the tip of the toggle has passed over the central 'V' notch, and the tip is now resting on the very edge of the block.

At this point one of two things can now happen.

If the pendulum has sufficient inertia still remaining it will continue to the left and the agate block will slide completely under, and out of the way of, the toggle. The toggle will then be left swinging free.

Otherwise if things are at the point where the pendulum has reached its maximum arc, then the agate block will still be under the toggle when the pendulum comes to a halt and reverses to swing back again to the right. As it does so the tip of the toggle will drop down into the notch and get caught there, as shown below.

The toggle now digs into the notch and the only thing that can happen is for the toggle to push the whole spring set, that it is attached to, upwards closing the contacts.

The actual moment of impulse, as the bottom spring is forced upwards by the toggle. The circuit is complete and the magnets are energisied attracting the pendulum as it swings back to the right.

Very soon after the toggle will flip itself over in the notch, and the contacts will open again. This brief closing of the contacts, and the subsequent pulse from the magnets, is all the clock needs untill its arc diminishes once again and the whole procedure repeats itself.