- "It was very like a clock, or a compass, for there were hands pointing to places around the dial, but instead of the hours or the points of the compass there were several little pictures, each of them painted with the finest and slenderest sable brush."
- —Description of the alethiometer[src]
The name of the object comes from the Greek aletheia (truth) and meter (measure).
The alethiometer was invented by Pavel Khunrath in Prague. The experimental theologian discovered that an alloy of two particular rare metals could be used to create a needle that pointed towards the truth. The first alethiometer consisted of this needle suspended over a celestial chart showing the signs of the zodiac, with Khunrath asking questions and receiving responses.
Khunrath later improved the alethiometer by using symbols from the memory-theatre to give himself a wider array of icons to draw upon. As his research went on, he realised that the meanings of the symbols already existed and that he was discovered them rather than inventing them.
When Emperor Rudolf II died in 1612 and Emperor Frederick succeeded him, research deemed occult was outlawed. Khunrath was burnt at the stake for heresy in the name of the Magisterium, but some of his instruments and notes survived. Scholars in more tolerant countries continued his work, naming his device the alethiometer.
Reading an alethiometer required particular skill and training. Although Lyra Silvertongue was able to do so intuitively in her youth, after puberty she had to relearn how to do it. Most scholars made use of reference books in order to decipher the meanings of the alethiometer's 36 symbols. Duke Humfrey had such literature in his library.
To read the alethiometer, the user first directed three needles to lie over certain symbols on the face of device to create a question. Then, the user held this question in their mind, without grasping at the answer, but being content not to know. At this point, the fourth needle swung into action, moving from one symbol to another to create the answer.
A person who was capable of reading an alethiometer was known as an alethiometrist. Known alethiometrists are:
The alethiometer had thirty-six symbols, each of which had countless meanings. Each symbol has its own article detailing its meanings.