The Amber Spyglass is both the name of the third and final book in Philip Pullman’s His Dark Materials fantasy series, and the name of a fictional object in those books. The object allows a person to see the mysterious Dust, without special conditions such as the Aurora Borealis occurring.
The Amber Spyglass is by far the most contentious of the three books of the series. The book concludes with the final defeat of the Authority, as well as what appears to be a veiled reference to sexual intimacy between the children-protagonists of the books. The book focuses on the war between Lord Asriel’s army and the Kingdom of Heaven, as well as the scientist Mary Malone and her travels in an alien universe and discoveries about the nature of Dust.
In The Amber Spyglass Mary Malone finds her way into a very different universe from either ours or the universe of Lyra. This universe is inhabited by a sentient race called the mulefa, who are very different in appearance and society than humans. They have no spines, and are diamond shaped. They have a long trunk which they use to manipulate objects, and also to communicate. They seem to live in a pre-tribal setting, with a low technology level and tight-knit communities. They also have a very well-preserved history, however, which appears to be orally passed down. It seems to go back about 33,000 years, to the time when Dust first began interacting with races throughout the universes, giving rise to modern consciousness.
They seem to have a very positive interaction with the Dust, with no Magisterium or similar body that is subject to the Authority appearing within their society. They have their own version of the story of Adam and Eve, but rather than viewing it negatively as an expression of First Sin, they see it positively. Perhaps because of this relationship to Dust, or perhaps for another reason, they are able to see the Dust with their naked eyes, and are able to tell Mary about it.
Originally, Mary did not set out to build the amber spyglass. She first tried to build something that would help capture the Dust and save the giant trees that the mulefa had noticed were dying. She made a sheet of lacquer from the sap of the trees, and happened to notice that when two of these sheets were held a distance apart and coated with oil from the trees, the Dust could be seen through them. The oil itself seems to have some sort of a relationship to the Dust, as the mulefa use it as part of their relationship with the seed pods from the giant trees, which seem to be their equivalent of daemons or souls.
Once Mary has discovered this use for her sheets of lacquer, the mulefa help her make a bamboo tube to mount two sheets in, resulting in the amber spyglass itself. The amber refers to the color of the lacquered sap, and not to literal amber. Mary goes on to use the amber spyglass to study the Dust and to determine that it is leaving the world.
Both the alethiometer and Aesahaettr, the golden compass and subtle knife that give their names to the first two books, require a particular state of mind to be properly used. The mind must be allowed to drift slightly while focus is retained, in what is called negative capability. The amber spyglass, however, does not require any special mental state. Simply looking through the amber spyglass allows Dust to be seen. However, if negative capability is used, the user’s consciousness leaves the body and goes into the Dust itself, allowing the user to actually experience the Dust more viscerally.