The difference engine was originally of gnomish design and manufacture (but said to have been inspired from some contraption they’d seen in one of the dwarven cities of the Crystal Peaks). Several of them were commissioned by the Empire to help tabulate the hundreds of thousands of responses from the decennial census. Rowena’s tinkering uncovered the machine’s ability to execute punched-card instruction rather than simply tallying and sorting the input cards.
Further experimentation removed gears and instruction cards from the equation entirely, relying first on pulses of light generated from a series of wheels and mirrors. Eventually, the technology was miniaturized using specially-cut, rotating continual light-enspelled gemstones or quartzite crystals.
Difference engines were instrumental in calculating the refraction indices and differentials needed to peer into the Ethereal and later, Aetheric planes. A difference engine specialized for maintaining a window or projecting an explorer’s shadow into the Aetheric plane is called an Aethercaster.
Whereas the Ethereal plane is composed of varying densities and concentrations of ether, the Aetheric plane is believed to be made up of pure information, the home to all knowledge and dreams of all the sentient races of the Prime. Entire branches of research at the University are devoted to the investigation, exploration and exploitation of the Aetheric thoughtscape. At least three native species have already been identified and are under observation: Muses, SHADEs, and aetherspiders.