Learning to use the alethiometer, Lyra and Pantalaimon discuss the possibility that after she sets the three symbol dials on her alethiometer, what drives the unfixed needle to circle round and stop at symbols that answer her question is a spirit. Or it might be elementary particles. A discussion of the photo-mill at Gabriel College follows:
At Gabriel College there was a very holy object kept on the high altar of the Oratory….At the height of the invocation, the Intercessor lifted the cloth to reveal in the dimness a glass dome. . .he pulled a string attached to a shutter above, letting a ray of sunlight through to strike the dome exactly. Then it became clear: a little thing like a weathervane, with four sails black on one side and white on the other, that began to whirl around as light struck it. (Northern Lights 149)
The Intercessor takes it as an illustration that “ignorance fled from the light,” but the white side of the vane, wisdom, “rushed to embrace it.” Now,
“… perhaps Pantalaimon was right. If elementary particles could push a photo-mill around, no doubt they could make light work of a needle” (NL 149).
Lyra has her doubts, and will later remember this conversation when she asks Serafina Pekkala about Dust, who replies that worries about it are a Church thing, of no interest to witches, but Lyra is left wondering if what pushes the alethiometer’s needle could be the same as the elementary particles the Intercessor claimed “pushed the little vanes around” of the photo-mill kept on Gabriel College’s high altar (NL 318).
Whatever acts upon the alethiometer’s unfixed needle, it remains a question why Lyra the child can interpret its movements in trance or intuitively, but the mature Lyra will need to study the voluminous commentaries on the symbols’ multi-faceted meanings in order to understand what she is seeing. I suspect this territory is where William Blake on innocence and experience, and the doors of perception, would be our best guide.
On the problem of radiometers (our world’s photo-mills): Radiometer.