This Study Guide consists of approximately 59 pages of chapter summaries, quotes, character analysis, themes, and more - everything you need to sharpen your knowledge of Dark Matter. The geisha mask is used to hide the identity of the man who abducts Jason. It is a symbol of that strange man. The Alethiometer. The alethiometer is a truth-telling device, a beautiful, exquisitely detailed instrument that Lyra Belacqua is able to read intuitively almost from the moment it is given to her. It can provide information about the past and present, and it can also suggest what might happen in the future if certain conditions are met.