The Alethiometer is a truth-telling device driven by Dust that is able to answer questions formed in the mind of the user. It is a symbol reader, with each symbol having an infinite number of meanings. A skilled user forms their questions by imagining how far down the particular meaning they are searching for is on the ladder of meanings for that symbol, and must old the three levels in their mind while the alethiometer makes its response by stopping on a symbol for each number of times that the meaning is down on the ladder of meanings. The name comes from the Greek word aletheia, or "truth", referring directly to the device's ability to give a truthful answer to any question which involved past occurrences, or even a limited extent of future ones. It is also referred to as a Symbol Reader, particularly by the Gyptians.
Dr. Lanselius tells Lyra the alethiometer originated in Prague, invented by a 17th scholar with an interest in astrology, investigating the influence of the planets. It was intended to respond to planets as the compass responds to the idea of north. Although he failed in his design, it was clear that the alethiometer was responding to something: Dust. The object had been likened to that of photons (light particles) that bombarded a light-sensitive metal; however, it seemed that whatever that altered the direction of the device was consciously doing so, rather than moving it in random directions. Only six alethiometers were ever created.
It was actually invented by Pavel Khunrath during the reign of Rudolf II (1576 - 1611).
The alethiometer that Lyra was given
|"lay heavily in her hands, the crystal face gleaming, the golden body exquisitely machined. 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 extraordinary precision, as if on ivory with the finest and slenderest sable brush."|
|The Golden Compass|
There were three winding wheels that could be turned so the shorter hands would point exactly in the center of any of the pictures. The longer fourth hand was more slender and seemed to be made of a duller metal would then swing like the needle of a compass.
Reading the Device
Reading the alethiometer is no mean feat; few can read it, and even then it would take a person's lifetime to proficiently read the device.
Lyra is the only known alethiometrist who can read it without the need of books that would help interpret the symbols of the device. However, she seemed to have lost the ability to read it with intuition as she entered adolescence:
|"Lyra turned one wheel, turned another, turned the whole thing round, and then looked up at Will, stricken. 'Oh Will,',she cried,'I can't do it! It's left me!'"|
|The Amber Spyglass (Knopf 518)|
|"'Well, well,', she (Mrs. Coulter) said. 'Fra Pavel must be getting quicker. When I knew him it would have taken him a month at least to read all that.'"|
|The Amber Spyglass (Knopf 343)|
Teukros Basilides is the alethiometrist for Lord Asriel
The Society of the Work of the Holy Spirit has a skilled alethiometrist who is unnamed.
Dame Hannah Relf is a skilled reader. It's not stated specifically that she has an alethiometer, but she must have access to one in order to teach classes in the subject.
Farder Coram knows all the details of how to read it from watching one read in Uppsala, but he says he couldn't read it without the books.
Master at Jordan College. He quotes predictions that the alethiometer has made in a conversation with the Librarian, and he had the alethiometer that Lord Asriel donated to Jordan College. He also had access to the books, but it is never stated explicitly that he reads the alethiometer or has the knowledge.