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high school; and they are in nearly every community, even the very small. Of course, many of these libraries are connected to the Internet. But it is very important to consider the other resources provided by these libraries. Thirty-five percent of all library visitors never use the catalog, and 12 percent use no library materials at all, but bring in their own materials. Clearly, libraries do something more than just supply data that could be gotten over the Web (see www.ubiq.com/weiser/SituationalAspectsofElectronicLibraries.html).

As the above examples illustrate, the existing information infrastructure often functions without calling itself to our attention. It stays out of sight, effectively not even noticed. So the first challenge for every-citizen interface is to be invisible (what I have called ''calm technology" elsewhere; see www.ubiq.com/weiser/calmtech/calmtech.htm).

As the above examples also illustrate, the existing information infrastructure is extremely widespread, found in every nook and cranny of our lives. The second challenge for the every-citizen interface is to be ubiquitous (see www.ubiq.com/ubicomp).

Finally, not addressed by the above examples but presumably clear to everyone, the current Internet is just the beginning. I like to think of it by analogy to television channels. Once upon a time we fretted about how we would manage a TV with 500 channels. How could we ever view them all? The Internet will give us 5 billion channels, one for every person on the planet-only about 30 million so far, but more are coming. And soon these channels will be multimedia, multiway video and sound using the Mbone. This kind of interconnection is a deep technical challenge to the current Web infrastructure, which cannot begin to support even a few multiway Mbone connections, much less 5 billion. I consider this to be a user interface issue because it is just this infrastructure that opens up the Web to use by anyone who can point a camera or talk on the phone. The third challenge for the every-citizen interface is to support billions of multiway real-time interactive connections.

Of these three challenges I believe that the first is currently the most promising of progress, the one most susceptible to interdisciplinary attack, and the one least well addressed by existing projects. How does a technology become invisible? To some degree, anything can, given enough practice. Invisibility is a property of people, technology, and the situation in which we find ourselves (a tiger invisible in the tall grass stands out at the zoo).

Some suggested challenges for developing a "science of invisibility" for a every citizen interface are as follows:

Human information processing includes operations at many different levels, the vast majority of them invisible to our conscious thought



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