He thought that the train would be perfectly safe because he knew how the signalling equipment of the time in that area worked; but he did not know that the train had stopped short of the track circuit, which would have reminded the signalman of its presence.
The train would be perfectly safe. How the signalling equipment of the time in that area worked. This was what he knew. He thought this. The train had stopped short of the track circuit. He did not know this. The track circuit would have reminded the signalman of its presence.