The lenses of the Persopolisian spectacles revealed the manipulating force fields which were used by the Persopolisian when they want to build something. They also showed grey mist when someone looked a Persoplisian or parts of a Persopolisian control console.
Janksia had such Persopolisian spectacles. He lost it and Sarah Jane Smith found it. When Sarah Jane looked through the glasses at Janksia, they revealed great swirls of grey mist undulating about Mr Ploughman which were invisible to everyone but Sarah Jane.
Later Rani Chandra put on the spectacles. She saw a grey trail on the street leading to Janksia. Sarah Jane and Rani got into Sarah Jane's car and went after the trail to find Janksia and the third artefact of the Persopolisian control console. (AUDIO: The Time Capsule)